Last Updated: 3rd August 2020

Inner-city Serpent  -  3.5ft adult female Aesculapian Snake at Regent's Canal 2016

Aesculapian Snake  (Zamenis longissimus, previously Elaphe longissima)

Here in the UK we have three native snake species and one non-native snake that has established breeding colonies at three different sites. The four snake species found are:

Native:    Adder (Northern Viper),     Grass Snake,     Smooth Snake

Non-native:    Aesculapian Snake

The fourth snake is the non-native Aesculapian Rat Snake, originally from mainland Europe, and is only found in three specific parts of the UK. Although considered non-native to the UK there are two well established breeding colonies of Aesculapian Snakes in Great Britain that have been in existence now for over 30 years and one newer colony, only recently reported (1st June 2020), that is estimated to have been around for 15-20 years. One colony is in Central London, England and the other two colonies are both in Wales. The oldest population of Aesculapian Snakes in the UK is in Colwyn Bay, Wales and the newest is in Bridgend, Wales. Outside of the UK the nearest populations of wild and native Aesculapian Snakes are found in NW France.

These long slender Rat Snakes, of the Colubridae family, are Old World Snakes and are one of Europe's longest snakes. They regularly grow to a length of 140-160cm. In warmer parts of Europe they can reach up to 180cm and have even reached 225cm on one occasion. This easily makes them the longest snake found in the UK, and one of the longest in Europe. The maximum weight for males is usually around 890 grams and 550 grams for females. These snakes are usually found across southern, central and eastern Europe and prefer the same method of incubating their eggs as our native Grass Snakes, using warm damp moist areas of rotting vegetation such as hay piles and compost heaps to provide the necessary heat. Aesculapian Snakes are the only semi-arboreal snake in Europe. Not only are they are excellent climbers but are equally at home high up in trees and bushes as they are on the ground. They can on occasion be found basking on the canopies of trees and tall bushes, or on roof-tops of buildings.

Adult female Aesculapian Snake

So where did they come from and how did the three separate populations of Aesculapian Snakes end up here in the UK? 

1) Colwyn Bay population of Aesculapian Snakes in Wales.

In 2006 the Welsh population of Aesculapian Snakes was estimated at around 85 adult and 365 juvenile specimens, and allegedly came about during the late 1960's after a gravid female snake, affectionately referred to as "Old Essie" by the 2003 assistant curator Peter Dickinson, escaped from the Welsh Mountain Zoo at Colwyn Bay and laid her eggs within the grounds of the zoo. The offspring then successfully bred and the population has thrived ever since in and around the zoo grounds. According to the NNSS website the first official record of these snakes living wild in Colwyn Bay was in 1970. They were first reported by the press during the early '70's. Software analysis has however suggested that several individual specimens probably comprised the founder stock rather than just one specimen according to the 2009 book "The Naturalised Animals Of Britain & Ireland" by Christopher Lever". This population has not spread far from the zoo in 50 years confirming that this species probably has a low dispersal ability, and is reliant on woodland connectivity to travel. It is also likely that due to the abundance of rodent prey surrounding the Colwyn Bay Zoo that these snakes are reluctant to leave this food-rich location. The main egg laying site for this snake population is suspected to be the manure dump at the Zoo. 

The Welsh Mountain Zoo at Colwyn Bay was founded in 1963 by Robert Jackson. Robert Jackson was an importer and dealer of reptiles, amphibians, mammals and birds. One of the many species he sold in the 1950's & 60's was the Aesculapian Snake. See link here

2) Bridgend population of Aesculapian Snakes in Wales.

On July 1st 2020 it was announced by Steven Allain and Dave Clemens that the British Herpetological Society had published their paper in issue 152, Summer 2020, of the Herpetological Bulletin, that announced a third population of Aesculapian Snakes living wild and breeding here in the UK. 

There is already the Aesculapian Snake colony in North Wales but this new population is in Bridgend, South Wales. The two Welsh colonies of Aesculapian Snake are nearly 200 miles apart. This is almost the same distance as the London Aesculapian Snake colony is from the Bridgend colony.

The first report of an Aesculapian Snake to be found in Bridgend came from a member of the public after an adult snake was found in a residential garden on the 19th September 2016, although this wasn't made public knowledge until nearly four years later. Further investigation found that these Aesculapian Snakes were also present at nearby allotments. When questioned at the time local residents claimed that these snakes had been known to be around in their area for around 15 - 20 years. With a railway line nearby this feral population of Aesculapian Snakes differs from the other two populations found in the UK because it has the potential to disperse and spread considerably further from where it has currently been recorded. 

It is unknown at this time how large this population is or how far it has spread. It is also unknown how these snakes came to be in the area. The paper by S.Allain & D.Clemens mentioned the possibility that the founding snake could be an escaped pet or a deliberate release. My experience is that this species of snake is not overly popular in the UK pet trade and few reptile keepers choose to keep or breed this species here in the UK so I believe it is unlikely that this new colony is the result of an escaped pet. And if someone kept just one specimen as a pet then it wouldn't be able to start a new colony of snakes on its own if it did manage to escape. I have my suspicion that this could well be a case of deliberate release by someone wishing to start a new Aesculapian Snake colony in the area and I would be surprised if the founding specimen or specimens didn't originate from the Colwyn Bay Aesculapian Snakes. Surveys and studies of this newly discovered snake population will now commence by ARC-Trust to try and estimate the size and range of this new population. Hopefully DNA testing will be performed at some point to establish whether these snakes originated from a specimen of Aesculapian Snake from either the Colwyn Bay or Regents Canal population.

BHS Herpetological Bulletin 152, Summer 2020, page 30 & 31

3) London population of Aesculapian Snakes.

By 2018 the London population of Aesculapian Snakes had seen 50 different adult specimens recorded and photographed by Will Atkins and in 2013 this population was then estimated at around 40 specimens. However numbers of these urbanised snakes seem to have fallen significantly in London over recent years, and in 2020 it is feared that there may be few of this once thriving population of snakes now left surviving. This population is confined to a small area of around 2 hectares surrounded by busy roads, and could only spread beyond this range by travelling along Regents Canal itself.

It would be easy for one to jump to conclusions but despite the obvious theory that the London population of Aesculapian Snakes derived from one or more escapees from London Zoo, this surprisingly isn't the case.

It is widely accepted that this population came about after about eight individual specimens were deliberately released in the mid 1980's from the "Centre For Life Studies", a building located at Zoological Gardens, Regents Park, NW1 adjacent to London Zoo and rented by ILEA (Inner London Education Authority facility for scientific experiments) along Regent's Canal. A well respected herpetologist I spoke to claims to know exactly which former ILEA staff member was responsible for releasing these snakes onto the banks of Regent's Canal.

In 2010 David Bird, a former zoo curator, told a reporter from the Camden Review, that the Aesculapian Snakes either escaped from or were deliberately released from the ILEA building: Camden Review article

Theses snakes were first reported in 1998 to TESL by Ester Wenman, who was at that time the head keeper of reptiles at London Zoo. This growing population of Aesculapians in London became common knowledge amongst many herpetologists in 2007 via an online herpetology forum and many traveled to London to find and photograph these snakes for themselves.

Christopher Lever discussed the London Aesculapians in his 2009 book "The Naturalised Animals Of Britain & Ireland" by Christopher Lever", and Will Atkins & Tom Langton then went into more detail about the origins of the London Aesculapian Snakes in 2011 when they wrote an account in The London Naturalist No.90, 2011 on page 93 & 94, giving this summary:

"A second feral population has been extant since the mid 1980s along a canal embankment habitat in Camden, north London.This was first reported to TESL in 1998 by Ester Wenman, then head keeper of reptiles at London Zoo. Aesculapian snakes had apparently colonised the area during an experiment reported by the British Herpetological Society Legal Officer, Peter Curry, who was working there and keeping this species at the Inner London Education Authority Centre for Life Studies at the time that it was closed down around 1986. One account was that eight snakes had been released ‘on the quiet’ around the time of closure to try to form a population, several of which were recaptured, but some remained at large.Those caught initially were being euthanized but the view was then taken to leave the others ‘to take their chances’ where they were. Ten years later, in an aviary close to the embankment, fragments of juvenile Aesculapian snakes were found in a laughing thrush Garrulax sp. aviary, suggesting that the snakes had bred."  The article also states, “Several newly born snakes were found in the basement of a building around 30 metres from the embankment in 2010, and breeding in that year was also shown in 2011 with a young 2010 cohort snake being located. To this date this is the only example of a non-native snake species breeding successfully and forming populations in the wild in London and the UK as a whole.”

The London Naturalist No.90, 2011, page 93 & 94

Jason Steel photographing an adult female Aesculapian Snake along Regents Canal in London, UK in 2016. Photo taken by Australian photographer Diane Paine.

Are these snakes a threat to our native wildlife?

The simple answer to this question for the two populations of Aesculapian Snake at Regents Canal and Colwyn Bay is no. Following ongoing studies of both the Aesculapian Snake populations in the UK by respected herpetologists including Wolfgang Wuster in Bangor, Wales, & Will Atkins in London it has been shown that the existence of these snakes has had very little if any negative impact on our native wildlife. This is largely because they feed almost entirely on common rodents which are in abundance around both zoos. In 2016 one adult Aesculapian Snake specimen regurgitated six rat pups when handled by a fellow amateur herpetologist and friend of mine.

These snakes also seem dependent on woodland habitat connectivity in order to spread. In 50+ years since their arrival neither of the UK populations of these snakes have been able to spread further than the sites where they are found. In London there simply aren't the necessary dispersal corridors available for the Aesculapian Snakes to disperse any further than they already have. And the population's distribution and reproduction is severely limited by the scarcity of suitable egg-laying sites.

With the undeniable climate change that is already here and taking place across the world, temperatures are on the increase. It is likely that the natural range of the Aesculapian Snakes found in Europe will change in the future. As temperatures continue to rise it is likely that many reptile species, including the Aesculapian Snakes, will move further north. It is only the English Channel that would prevent any possibility of theses snakes from returning to Britain in future years. It is highly likely that they have lived beside our native species in the past and could probably do so again without issue if they could reach our southern shores.

With the newly discovered population of Aesculapian Snake at Bridgend, Wales it is uncertain at this time what impact these snakes at Bridgend will have any the local environment as they have the potential to disperse. However Aesculapian Snakes are found across much of Europe living side-by-side with many of the same species of wildlife that we have in the UK without any issues.

Adult female Aesculapian Snake

Are these snakes dangerous?

No, not at all. The Aesculapian Snake is non-venomous and not an aggressive species. It also lacks the size or strength to inflict any harm to either humans or pet cats & dogs. Unless you're a rodent, a small bird or a young lizard, then you're quite safe from these snakes.

Adult female Aesculapian Snake by Regent's Canal, London

The London population of Aesculapian Snakes can be found along the length of Regent's Canal as it runs past Regent's Park, living on both sides of the steeply sloped banks that run parallel to the canal. 

Adult female Aesculapian Snake

Aesculapian Snake specimens found in London tend to be slightly larger than those in Colwyn Bay and this could be one possible effect of in-breeding by the Welsh snakes, if there is truth in the rumour that the Welsh population of Aesculapian Snake all derived from a single escaped specimen. A 1960 photo of an Aesculapian Snake supplied by Robert Jackson, a well known reptile dealer and founder of the Welsh Mountain Zoo, depicts an Aesculapian Snake of good size suggesting that the original escapee that formed the wild population of Aesculapian Snakes in Wales may have been larger than those Aesculapian Snake specimens now found there today

The Welsh population of Aesculapian Snakes is now the most northerly extent of this species' range and this could explain why the Welsh Aesculapian Snakes are not only shorter but also marginally lighter in colour than Aesculapian Snakes found in warmer and more southern parts of Europe where they occur naturally.
These snakes are native to central and eastern Europe and it is believed that the Welsh population derived from snakes originating from Central Europe, possibly Italy. However as yet no DNA testing has been done, or results released, to confirm the origin of the London population of Aesculapians.

Adult female Aesculapian Snake

Unlike all the other snake species found in Britain, it is the male Aesculapian Snake that is usually longer than the female. The female has greater girth but the male tends to be much longer. The female pictured above had a total body-length of just 3.5ft. A male specimen with equivalent girth would probably have been 5ft+ in length.


Adult female Aesculapian Snake

So what makes the Aesculapian Snake so special?
The Aesculapian Snake is the only non-native snake species to ever form a successful breeding colony in the UK. Not only have they managed to achieve this in two separate locations, but they have also managed to do this without upsetting the delicate balance of the ecosystem in which they are found and the surrounding wildlife. However, two of the colonies of Aesculapian Snake found in the UK are within the immediate proximity of local zoos and are probably dependent on the food source of rats and mice attracted to these zoos. Should either zoo close down then it is questionable whether the rat numbers in the area would still be sufficient to sustain either snake population. The Aesculapian Snakes found at Regent's Canal are even more special in my opinion for several reasons: Firstly, they are an egg-laying species which means they are far more dependent on suitable conditions to successfully hatch their young. They have also managed to survive for 30-35 years, against all odds, in the centre of one of the busiest capital cities in the World. They have been given no help to aid their conservation over the years and to continue surviving they just need to be left in peace. And whilst living on the Banks of Regent's Canal and within the grounds of London Zoo they provide a valuable vermin control service free of charge as they feed on the rats and mice that plague most zoos.

Notice the short and rapidly tapering tail indicative of a female Aesculapian Snake

Adult female Aesculapian Snake

These elegant snakes range in colour from light golden-brown to dark brown with white flecks and a creamy yellow underside. Aesculapian Snakes have unkeeled scales that are very smooth to the touch and this snake can have a very shiny appearance with an iridescent sheen in bright sunlight. Their overall appearance is often compared to that of a Twix wrapper.

Adult female Aesculapian Snake

This adult female specimen at London exhibits several scars along her body. These may have been caused by attempted predation by birds, foxes, domestic cats, or defensive rodents and some snakes have suffered as a result of encounters with local council workers or groundsmen using strimmers to cut the grass. Groundsmen workers at ZSL bear witness to Magpies being seen attacking these snakes on several occasions.


Adult female Aesculapian Snake

Will Atkins has been photographing and recording individual specimens of the Aesculapian Snake population in London since 2007. His photographic database allows him to identify individual snake specimens by studying unique scale markings on the head of each snake. This close-up shot of the snake's head shows the smooth un-keeled scales of the adult female Aesculapian Snake, number 15 of the London population, identified from Will Atkin's database.

This individual snake has been recorded on both sides of the canal. Whether it uses the footbridges or whether it swims across the canal is uncertain as these snakes have been filmed by members of the public by the footbridges. In 2011 I spoke to the owner of a canal-boat moored along Regent's Canal who claimed to have once seen a 6ft snake swimming in the middle of the Regent's Canal. In other European countries, such as France, where the Aesculapian Snake is considered native the typical range for a male specimen is around 1.14ha, however males have been known to travel distances of 2km in search of females during the mating season. Likewise females can travel similar distances in search of suitable egg-laying sites. 

For reference see page 3 here:  LINK 

Adult male Aesculapian Snake at Regents Canal, 24th May 2012.

Juvenile Aesculapians usually display a yellow collar making them easy to confuse with juvenile Grass Snakes. However Juvenile Aesculapians can lack the dark collar that is nearly always adjacent to the yellow collar found on Grass Snakes. This yellow collar fades and then disappears as the Aesculapian Snake reaches maturity, unlike Grass Snakes which usually retain this yellow collar throughout most of their life. Aesculapian Snakes are egg-laying snakes and usually produce clutches of 5 -20 eggs with 5 -11 being common. These eggs hatch after 6-10 weeks depending on the weather and incubation temperatures. 

Adult male Aesculapian Snake

In captivity Aesculapian Snakes can live for 25 - 30 years, however due to predation it is unlikely that wild specimens would live that long. Aesculapian Snakes reach sexual maturity after approximately 4-6 years. Male Aesculapian Snakes reach sexual maturity when they reach around 100cm in length, and females at just 85cm in length.

Adult male Aesculapian Snake, at Regents Canal, May 2012.

Slithering along the branches of this tree, the Aesculapian Snake is a very competent climber. They use their strong prehensile tail to grasp a firm grip when climbing or when being handled.


Adult male Aesculapian Snake with a total length of 4 ft 5 inches, including tail.

The Aesculapian Snake is not as timid as our native Grass Snake and can often be approached for photographs without disturbing it or causing it to flee. They rely heavily on their excellent camouflage and will often remain completely motionless until they are sure that you have seen them. Although usually a shy and secretive species due to the high levels of human traffic that pass by the London Aesculapian Snakes everyday some specimens have become pretty fearless of human contact. There have been several occasions when these snakes have been spotted and filmed crossing busy pathways in the middle of the day when there are plenty of people about.

Adult male Aesculapian Snake with a total length of 3.5 ft at Regents Canal 2019.

If handled Aesculapian Snakes may initially bite but usually calm down quite quickly, and once they no longer perceive you as a threat they can be very relaxed in your hands. Being constrictors, these snakes have a very strong grip. When startled it's surprising how firmly they can squeeze your hand. Technically by handling a non-native species you are committing an offence when you release it again into the wild without a licence, so I don't encourage anyone to handle a wild Aesculapian Snake in the UK. 

Adult male Aesculapian Snake (Snake 27 on Will Atkins records),  at Regents Canal, 11th July 2011.

One of two specimens photographed high above the ground basking in the canopy of a large bush at London in 2011. Aesculapian Snakes prefer slightly warmer temperatures to our native snakes and Aesculapians have been observed when temperatures have been between 16 - 25 degrees C, with 21-24 being the favoured range.


Adult female Aesculapian Snake (Snake 7 on Will Atkins records), at Regents Canal 11th July 2011. 

The second of two specimens photographed high above the ground basking in the canopy of a large bush at Regent's Canal, London in 2011.

Adult female Aesculapian Snake (Snake 7 on Will Atkins records), at Regents Canal 11th July 2011. 

Feeding mainly on mice, voles, young rats and other small rodents these non-venomous constrictor snakes will also eat lizards, small birds and eggs if available. Like most snakes the Aesculapian Snake sheds its skin periodically in one complete slough. Apart from a noticeable dulling in colour and pattern, one obvious indication that a snake is due to slough is the clouding over and bluing of the scale covering the eyes of the snake as pictured above. This eye-scale will shed first and then the rest of the snake's skin will usually shed a few days later as a complete slough.


Adult male Aesculapian Snake found slithering through low vegetation at the edge of the tow path along Regents Canal 2019

Male Aesculapian Snakes, like many other species of snake, engage in combat with rival males for the right to mate with female Aesculapians. These battles usually consist of wrestling matches where the two male snakes intertwine their bodies and try to force their opponent to the ground until one male gives in and retreats. If the snakes are similar size and equally matched in strength then these fights can last for over 90 minutes and frustrated snakes can resort to biting each other to win. This behavior has been excellently captured on film in the Czech Republic where these snakes are classed as critically endangered.  Watch video here.

Adult male Aesculapian Snake at Regents Canal 2019

Adult male Aesculapian Snake at Regents Canal 2019

Adult male Aesculapian Snake at Regents Canal 2019

Aesculapian Snakes have angled ventral scales on either side of their body which grip extremely well to rough tree bark and enable them to climb vertical tree trunks in search of basking opportunities in woodland or to hunt for birds and their nests in the branches. Despite the excellent climbing abilities of the Aesculapian Snake most specimens are found on the ground in the London and Welsh populations, as well as in the Aesculapian Snake's natural habitat in European countries, as mentioned in "The Snakes of Europe" by Guido Kreiner.

Adult male Aesculapian Snake at Regents Canal 2019

Adult male Aesculapian Snake at Regents Canal 2019

Members of the public walk past blissfully unaware of the 4ft+ slithering serpents that share this habitat. Due to the constant exposure to high levels of human traffic passing by Regents Canal the London Aesculapian Snakes have learned to have little fear of humans and are far easier to photograph. Photographing this species in public provides an excellent opportunity to talk to curious passersby and educate them about these beautiful creatures and their role in the ecosystem. The reaction from members of the public is usually one of complete surprise that these exotic creatures live in London, followed by fascination.

Adult male Aesculapian Snake at Regents Canal 2019

Aesculapian Snakes don't usually rely on ambush tactics and are rather more of an active hunter. Prey is often hunted and subdued in its own hiding place. Adult rodents are usually killed by constriction before being swallowed head first. Many Aesculapian Snakes exhibit scars possibly obtained from previous encounters with the sharp teeth of defensive rats.

Adult male Aesculapian Snake at Regents Canal 2019

Adult male Aesculapian Snake at Regents Canal 2019

Adult male Aesculapian Snake at Regents Canal 2019

Adult male Aesculapian Snake at Regents Canal 2019

Adult female Aesculapian Snake at Regents Canal 2019

Adult female Aesculapian Snake at Regents Canal, April 2019

Adult female Aesculapian Snake at Regents Canal 2019

This 4ft adult female Aesculapian Snake was found coiled on top of a log-pile in dense woodland habitat along Regents Canal. Its entire body was in the shade with just its head exposed to occasional flickering sunlight.

Adult male Aesculapian Snake at Regents Canal 2019

Adult male Aesculapian Snake at Regents Canal 2019

Adult male Aesculapian Snake at Regents Canal 2019

Do Aesculapian Snakes bite?

Aesculapian Snakes are a usually calm species and some may not bite even when handled. Some specimens do hiss and strike when handled but this is often with a closed mouth to serve as a warning. Others may make a strike and bite without attempting to inflict any real harm, just to get you to release them. It is reported that sometimes Aesculapian Snakes will inflate themselves in a threat display but this is not something I have witnessed myself.

I must stress that there is no chance of being bitten by one of these snakes unless you try and pick one up! They will always flee rather than confront a human.

The bite marks shown in the image above were inflicted by an unusually defensive adult female Aesculapian Snake.  This account is by "someone" who picked up a wild Aesculapian Snake along Regents Canal in 2016:  

"I spotted a large adult female Aesculapian Snake on the canal's edge, mosaic-basking amidst grass and dead twigs on the ground. Only a few inches of the scales on the middle of the snake's upper body were visible, as the rest of the snake was buried beneath the protection of the surrounding foliage. When I carefully picked up the snake to photograph the head for identification purposes, to my complete surprise, an angry, wide-mouthed head quickly spun round and latched onto my wrist. Having never experienced any signs of real aggression from Aesculapian Snakes during previous encounters, I was very surprised by how intent this snake was in defending itself from what it perceived to be a potential predator. It wasn't just biting me, It was rotating and twisting its entire body around in my hands whilst continuing to clamp its jaw around my wrist. It really meant business! After about 10 seconds it released the grip that its jaws had on my wrist, and it immediately turned its attention to my hand and began biting again. Then released, and then bit again! Then released, and then bit again!

It took me a while to realise that this snake, although drawing blood with every bite, was incapable of inflicting any real harm or pain on me. It had extremely sharp little teeth but lacked the sufficient clamping power in its jaws to do me any real damage. After a few minutes, the snake also came to the same conclusion, and once it also realised that I wasn't actually a threat or causing it any harm it began to calm down. After a while it became quite docile and was content to slither around or just relax in my hands and enjoy the warmth for a while before being released back to the exact spot where it was found."

Although considered completely harmless many colubrid snakes have very slight traces of very mild venom in their saliva produced by the Duvernoy's gland. Studies on Garter Snakes have shown that this mild venom could aid subduing mammalian prey when the snake grasps and holds the prey in its jaws for several minutes. Even though Aesculapian Snakes have tiny teeth, and are incapable of causing any real harm or pain to humans, the small puncture wounds can cause quite a reasonable amount of blood to flow from the wound making it appear to be far worse than the superficial scratch that it actually is. Jonathan Cranfield, of Herpetologic, has commented that this "suggests that there are anticoagulant enzymes at work" from the Aesculapian Snake's saliva.

Read the paper by W & F Hayes here.

Aesculapian Snakes In The News

These Aesculapian Snakes living in London have made the news headlines many times over recent years but May 2014 saw a series of disgraceful reports by the British media about the Aesculapian Snake colonies found in the UK. These sensationalised and scaremongering stories were full of false information and inaccurate reports with ridiculous claims and headlines including the Daily Star's "KILLER snakes that are capable of crushing small children to death are on the loose in Britain! " the Daily Mail's "London hit by outbreak of invasive eight foot snakes that could kill cats or small dogs!" and the Metro's "Army of 6ft 6in snakes capable of killing young children on the loose in London"

Daily Star      Daily Mail       The Mirror (amended)       UK News Yahoo      International Business Times      Travel AOL      Metro      Hackney Gazette

Less dramatic reports from these news websites:

Camden New Journal      London Live      The Islington Tribune      Express      Independant      Daily Post      Vice (excellent article)

Being classed as a non-native species are the Aesculapian Snakes likely to be removed?

Despite these snakes posing little if any threat to our native wildlife (excluding mice and young rats) in 2013 the Government agency 'LISI' (London Invasive Species Initiative) decided that these Aesculapian Snakes were a species of concern and called for the snakes to be eradicated in the UK, quoting them as a "Species of high impact or concern". You can download the list of "Species of concern in London". Thankfully LISI seemed to listen to experts on these snakes and in 2014 LISI responded to the sensationalized media stories and released the following statement alleviating any unnecessary fears and stating that they had no immediate plans to remove these snakes from the wild at least until further studies of their impact on native wildlife have been carried out:

 Killer snake headlines debunked

"There have been some interesting headlines over the weekend regarding Aesculapian snakes in London, such as the Daily Mirror’s ‘Colony of killer snakes ‘capable of crushing small children to death’ on loose in London’.

The London Invasive Species Initiative (LISI) has put together some information which we hope will clear up some inaccuracies. Below is our original statement, in response to a request for information on their population in London. Note that LISI is not calling for the eradication of the species in London, as reported in some media.

'The species of concern list for the Greater London area has been compiled by a range of industry professionals and land managers within London and is reviewed and updated quarterly. This list does indeed include the Aesculapian snakes that are being referred to, although no action that I am aware of has been taken to remove this population, nor does LISI have any plans to do so at present. This species is listed in the Wildlife and Countryside Act 1981 meaning it is illegal to allow the species to spread or escape into the wild. At present there is limited information on what effects the species may have on our local ecosystems and further information would be hugely valuable in developing appropriate management plans for this population’.

LISI would require further information and monitoring of this species before advising on any further action. With so many other invasive non-native species having a detrimental effect on our environment, it is not feasible to spend limited resources on a species that does not at present seem to be having a significant impact on our ecosystems.

As for the concern about people’s safety, when left alone Aesculapian snakes are a docile and non-venomous species. Please rest assured that your children will not risk being crushed by snakes whilst wandering through central London."

The decision on what action should be taken regarding any non-native species is usually made by the Non-Native Species Secretariat (NNSS). The NNSS undertakes risk assessments for any non-native species and would consider many criteria such as:  Is the species likely to spread? Does it feed mainly on other non-native species or rarer native species? Is it a threat to people? Is it a carrier of dangerous pathogens that could affect native species? If such criteria are used to make a decision on the Aesculapian Snakes in the UK, and if common sense prevails, then hopefully those in power will agree that these snakes pose no threat to people and very little, if any, threat to our native wildlife and could be safely left to their own devices. 

Speaking to Brian Banks, previously involved with the Natural England project to remove American Bullfrogs from the UK in the late 90's, he made it known that the project cost a six figure sum back then to remove the American Bullfrogs from sites across the UK. The American Bullfrogs were a highly invasive species and a very serious threat to our native wildlife. It's hard to imagine that a now poorly funded Natural England would find the necessary funds to consider the Aesculapian Snakes a threat serious enough to warrant such a huge expenditure. 

Aesculapian Snakes are still under threat from government action though and on 15th October 2019 the House of Commons Environmental Audit Committee released their First Report of Session 2019 on Invasive Species. The Aesculapian Snake was listed as a "species which are already established in GB and which are potential priorities for rapid eradication".

Adult male Aesculapian Snake 2012

Adult male Aesculapian Snake 2012

So what does the future hold for the London Aesculapian Snakes?

With many people incorrectly pointing the finger at ZSL fbeing responsible for the escape of the original Aesculapian Snakes that founded the London snake population, in 2016 rather than attempting to remove the snakes from Regents Canal, based purely on my own observations, the action that appeared to have been taken was to lay high numbers of rodenticide bait traps in the areas that these snakes were known to use as feeding grounds. By reducing the available prey for the snakes it has made it far harder for them to survive.  It's also highly likely that some snakes have been killed as a result of secondary poisoning after feeding on poisoned rodents. In May 2020 I was emailed after a member of the public found a dead adult Aesculapian Snake at Regents Canal. The dead snake showed no signs of injury and is likely to have died as a result of secondary poisoning. This reinforces my views that at least part of the blame for the dramatic reduction of Aesculapian Snakes at Regents Canal is likely to be due to these rodenticide bait traps used by ZSL.

Other Aesculapian Snakes have also suffered at the hands of selfish collectors and I have personally witnessed some members on reptile forums boasting of their intent to catch and keep wild specimens from the London Aesculapian Snake population. Numbers may also have fallen due to a lack of breeding success with a short supply of suitable rotting vegetation or manure piles needed for egg incubation. It is also very possible that some specimens may have been deliberately killed by ignorant people who fear snakes. 

In 2019 the number of rodent traps being I observed in the area seemed to have been reduced slightly from 2016. And with no immediate action being planned to remove these snakes it is hoped that they will be left free from persecution and be allowed to live in peace. With so many other more harmful and invasive species such as the Grey Squirrel now being accepted as part of the British wildlife it is hoped by many that these small and restricted populations of harmless snake will also be one day accepted too.

Adult Aesculapian Snake specimens have been recorded in London as recently as 2nd August 2020, by Lawrence Hill who also found a slough (old shed snake skin) along the banks of Regents Canal on the same day.

Although breeding of the London Aesculapian Snakes has obviously successfully occurred many times since the 1980's there seems to have been limited success in recent years. To the best of my knowledge there have only been 2 juvenile specimens recorded in the last 10 years in London. The first by Will Atkins and the last recorded on May 16th 2017 by Chris-26 on

August 2019 - As part of a debate on the future of Aesculapian Snakes in the UK, held on Facebook , world renown herpetologist Dr Wolfgang Wüster made the following comments in support of these snakes:

"I always get a chuckle out of these discussions of introduced species and the supposed threat they pose to natives. The underlying assumption (as in so much of the UK herp conservation scene) seems to be that the status quo, with our native species in the habitats they've always occupied, is still on the menu. Sorry folks, but that is just wishful thinking. Climate change is in progress, and we are seeing more of its effects every year. And while countries sign pious pledges in Kyoto, Paris and elsewhere, a look at the global scene right now (Trump, Bolsonaro etc.) suggests that it would take an unusual degree of optimism to believe that humanity has the collective will and the structures in place to significantly reduce emissions to the levels required to prevent the worst of climate change. We are in for a rough ride.

With climate change as forecast in any of the current humans-doing-too-little-too-late scenarios, not a single global ecosystem will be unaffected. "Nature", in the sense of environments unimpacted by humans, is effectively dead. There's a word for that: the Anthropocene. We are in it, and we are running the show. And since that is where we are, I suggest we would be better off owning it and trying to make the least worst of it, than pretending it's not happening,

For biodiversity, that means that the status quo is not an option. Organisms that can swim or fly will adjust their distributions accordingly under their own steam. It's already happening. Small terrestrial organisms generally don't have that choice in our fragmented landscape. So our options are to do nothing while we pretend that we don't want to interfere with a non-existent nature, while we watch the less adaptable species disappear and Britain's biodiversity decline, without any new diversity coming in to replace what is lost, OR we can decide to manage the situation and maintain overall biodiversity, and that could include welcoming non-native central European species that will now come under pressure in the southern parts of their distributions. The Aesculapian snake (as well as wall and green lizards and other Central European species) are perfect examples of that. They already interact with the same species as our natives in their current native range (so that chances of a disastrous impact are minimal even if they were to spread), and they are likely to end up having a hard time in parts of their native ranges. Why not welcome them here?
Note that I am ABSOLUTELY NOT advocating a free-for-all! We don't want introduced bullfrogs, corn snakes, Russian ratsnakes, red-eared sliders or other species from the other side of the world to proliferate here. But species from neighbouring regions that would get here anyway but for the Channel? I really think we need to rethink our attitudes there, and take into account the bigger picture of where we are headed."  -  
Dr Wolfgang Wüster

Is it possible some of the London Aesculapian Snakes did originate from London Zoo?

There is an interesting piece written on pages 181-182, in the book "Wild Animals in Captivity" by the late A.D.Bartlett, the superintendent of Regents Park Zoo during the late 1800's. He tells of his experiences where wild-caught brown mice were introduced to snake enclosures as a source of live food. If the mice weren't caught and eaten by the snakes fairly quickly, then the mice would gnaw their way out of the enclosures, leaving a rodent-sized hole for the snake to also escape from. The practice of feeding these wild-caught live brown mice was stopped once the mistake was recognised, but not before a highly venomous cobra had escaped. Luckily this cobra was eaten by another snake in the adjoining enclosure. But A.D.Bartlett also recalls:

"Years after the old reptile house had been disused, harmless snakes that had escaped in this way were found in the mill-room underneath the old house. They had doubtless lived upon the rats and mice that swarmed in this place."

The full book is available to view on-line here:   Wild Animals in Captivity - by A.D.Bartlett

With this information available it's easy to see how someone might question whether there is an unlikely possibility that maybe some of the specimens of Aesculapian Snake still found along Regents Canal could indeed have originated from escapees from ZSL? 

Despite some claims that ZSL never kept Aesculapian Snakes at their zoo, page 6 of the 32nd Edition, Zoological Society of London guide book dating back to 1935 (as seen below) confirms that Aesculapian Snakes were indeed one of several species of European snake kept at London Zoo in an "outdoor reptile rock garden".  Aesculapian Snakes were also listed as a species kept at London Zoo on page 5 of the 1928 26th Edition of the ZSL guide book and the 30th Edition as well. These guide books prove that the Aesculapian Snake was kept at ZSL at the very least between 1928 - 1935.

The Zoological Society of London's Reptile Rock Garden was built in 1928 and London Zoo continued to stock this outdoor enclosure with European snakes until the early 1960s. How many of those years saw Aesculapian Snakes held in captivity at the zoo is uncertain. 

1935 32nd Edition, Zoological Society of London guide book

Clinton H. Keeling (1932 - 2007), a former zoologist and historian of British Zoos, wrote many books on the subject of zoology. In his 1988 Clam Publications book 'They All Came Into The Ark' he discussed a Master J C Dendy. It is believed that Master J C Dendy was a young man in private school who "added a few non-existent years to his age" so that he could go to war to defend his country during World War 1 in 1915. Master J C Dendy had a large collection of herpetofauna and before he left for war he donated his entire collection of reptiles and amphibians to London Zoo on 16th July 1915. One of the many species kept within his collection was the Aesculapian Snake. Master J C Dendy was one of many who did not return from the war.  See link here: Malcolm Peaker Zoology Weblog
This is yet further supporting evidence confirming that Aesculapian Snakes were once kept at London Zoo. But even though we know for sure that ZSL did keep Aesculapian Snakes in the first half of the 20th century my research has found nothing to suggest though that London Zoo was keeping Aesculapian Snakes, in their private or public collections, until anywhere near as recent as the 1980s when the London population of feral Aesculapian Snakes in believed to have been established.


Were Aesculapian Snakes once native to the UK?  -  Fossil Remains of Aesculapian Snakes found in Suffolk & Essex

There have been a few discoveries in the UK of ancient fossil remains of Aesculapian Snake dating back to the warm end of the Pleistocene Period (around 11,700 BC) found in Suffolk and Essex (B.H.S. Bulletin no.50 1994). So although now considered a non-indigenous species many people are starting to accept that the Aesculapian Snake was probably once native to the UK many years ago when the climate was warmer, before being driven south by the arrival of subsequent glacial periods. This topic is covered in the 1998 book "Pleistocene Amphibians and Reptiles in Britain and Europe" by Professor J. Alan Holman. DNA analysis has confirmed that the isolated Aesculapian Snake populations in Northern Europe are proof that the range of the Aesculapian Snake has expanded and contracted slowly over long periods of time when necessary to cope with changes in climate as the Earth warms and cools. See article here: Relics Of The Europe's Warm Past - Phylogeography Of The Aesculapian Snake

Fossilised remains of Aesculapian Snakes have been found in the UK at these three sites: East Farm, Barnham, Sussex (discovered in 1994)  &  Beeches Pit, West Stow, Suffolk (TL798719 discovered in 1991)  &  Cudmore Grove, Essex (discovered in 1990). 

One must also consider the possibility that these fossils are the remains of yet more feral populations of Aesculapian Snake that either escaped from captivity or were deliberately released, as it is often reported that both the Greeks and the Romans kept Aesculapian Snakes in temples for healing and fertility rituals. However, the Mycenaean civilisation of early Greece (1600BC - 1100BC) never made direct contact with Britain and the Romans did not come to Britain until 43AD, so if the fossils are dated correctly then this hypothesis is highly unlikely.

Purchase "Pleistocene Amphibians and Reptiles in Britain and Europe" by Professor J. Alan Holman. 

With fossil remains of Aesculapian Snake having been found at three separate locations in England which date back to around 11,700 BC we should accept that it is highly likely that this snake species was indeed once native to the UK when the climate was slightly warmer than it is now. The range of the Aesculapian Snake once stretched as far north as Denmark, further north than England. And until around 6500 BC mainland Britain was joined by land to the European mainland allowing Aesculapian Snakes to travel north and extend their range as necessary. So why wouldn't this species have also once been resident in the UK as well?

Whilst Britain focuses its conservation efforts and reintroduction programs on other species including the Sand Lizard, Natterjack Toad and Pool Frog, at sites across the UK, why are we standing by and allowing the only two established and naturalized populations of Aesculapian Snake in the UK to dwindle and decline? And worse still why are we even considering their deliberate eradication if this species was previously found in Britain anyway?

Should these current introduced British populations of Aesculapian Snake therefore, whether intentionally released or accidentally escaped, now be considered as a reintroduction success story of a lost reptile species returned to Britain? With many specimens of the London population of Aesculapian Snakes having already been captured and taken from the wild by reptile collectors isn’t it about time this species was afforded the same level of protection by UK law as our other rare herpetofauna?

This map shows the range in 2020 for Aesculapian Snakes across Europe. See detailed ICUN Red List map hereSee also European Environment Agency Map

The Aesculapian Snake is one of four species of Rat Snake currently found in 31 countries across Europe. It is known that their range once reached far further north than it does now when the Earth's climate was warmer. This vast range may have been contributed to by escaped specimens from when the Romans kept Aesculapian Snakes during the Roman occupation of Europe. Although some herpetologists claim that there is little or no truth behind the "myth" that the Romans kept Aesculapian Snakes, other historians claim that not only were the snakes kept in temples for rituals and ceremonies but they were also kept in homes as "house snakes" to serve as vermin controllers. (see link here)

In the last 150 years Aesculapian Snakes have gone extinct in five northern countries with Denmark previously being the northern most part of their range until around 1863 when the last of the Aesculapian Snakes in that region died out.  Article 1  &  Article 2

Albino and Melanistic Specimens

Both albino and melanistic specimens of Aesculapian Snakes have been found living in the wild in Austria, Slovenia and Italy but these are incredibly rare. There are no records of any such specimens ever being found in the UK. In Greece grey morphs of the Aesculapian Snake can also be found. Striped specimens have been found in Pavia, Italy.

1) Read 2003 article on first Albino specimen in Slovenia here.    2) Read 2018 article on Albino specimens in Slovakia here.   

3) Read account of striped specimens found in Pavia, Italy.

Here's a photo of an albino Aesculapian Snake in captivity:  Zoochat

Where can I find wild Aesculapian Snakes? shows records of sightings across Europe including some from both Wales and London.

ARC Trust also shows approximate records for sightings in Wales here: Wales Online Amphibian & Reptile Atlas

Aesculapian Snakes, name and mythology

The scientific name "Zamenis" originates from the Greek language, with "Za" meaning "great" and "menos" meaning strength.

Aesculapian Snakes get their common name from the Greek god Aesculapius / Asclepius, the Greek god of healing / medicine, who was the son of Apollo. Aesculapius was reputed to have mystical healing powers and the ability to transform himself into the harmless Aesculapian Snake.  The skin-shedding of the Aesculapian Snake was seen as a symbol for rebirth and renewal. In Greek mythology the god Zeus killed Asclepius with a thunderbolt as a punishment for accepting money in exchange for resurrecting the dead. Once killed, Zeus placed Asclepius among the stars as the constellation Ophiuchus also known as the serpent bearer.

Aesculapian Snakes were used in ancient temple ceremonies for healing and sexual virility rituals performed by both the Greeks and the Romans. The Greek god Aesculapius is often depicted holding a snake-entwined staff. This staff became a symbol for healing which is still used in modern medicine today and can often be seen displayed outside pharmacies. The second symbol is the Caduceus, a short staff entwined by two serpents often surmounted by wings.

Aesculapian Snakes on TV

In 2015 the BBC's "One Show" asked me to feature on the program as part of a story they were going to run on the Aesculapian Snakes in London. Following my recommendation they featured the foremost expert on the London Aesculapian Snakes, Will Atkins. At the last minute the BBC sadly chose not to interview myself in the end and instead replaced me with the Greek historian, Simon Chaplin. The finished piece was however both interesting and informative and portrayed the snakes in a positive light. Watch the video here:    Watch BBC One Show     

London Aesculapian Snake sightings on YouTube, Twitter, Facebook, on the internet and sent to me via email.

IMAGE - 2nd August 2020, Lawrence Hill sent me a photo of an adult Aesculapian Snake found found basking within the grounds of ZSL. Lawrence also found a slough along the banks of Regents Canal.

IMAGE - 18th May 2020, 'Alexswe' recorded an adult Aesculapian Snake found on the footpath by Regent's Canal. (iNaturalist)

IMAGE - 18th May 2020, a member of the public sadly sent me a photo of a dead adult Aesculapian Snake found on the footpath by Regent's Canal.

IMAGE - 25th September 2019, Chris-26 recorded a sighting of an Aesculapian Snake found by Regent's Canal on October 5th on iNaturalist.

IMAGES - 26th July 2019, a series of photos of an Aesculapian Snake at Regent's Canal were published on Facebook by Andi Roy.  See images here

VIDEO - On 29th April 2019 another Aesculapian Snake was filmed crossing the path by the same bridge over Regents Canal in London by a member of the public, and shared on Twitter.
See the video here:  Aesculapian Snake on Twitter 

VIDEO - 23rd April 2019 an Aesculapian Snake was filmed crossing the path by a bridge over Regents Canal in London by Natalie Tambini, a member of the public, and shared on Twitter.
See the video here:  Aesculapian Snake on Twitter  

IMAGE - 23rd September 2017 - Another image was captured by a member of the public as an Aesculapian Snake openly crossed the path at Regent's Canal:  See image here

IMAGE - 11th June 2017 - An image was captured by another member of the public, Dimah Hanson, who posted on Twitter asking ZSL if they'd lost any of their snakes?  See image here

IMAGE - 11th June 2017 - An image was captured by a member of the public, David Ponsford, who posted on Twitter asking ZSL if they'd lost any of their snakes?  See image here

IMAGE - 26th June 2015 - An image was posted on Flickr by Julian Tysoe of Aesculapian Snakes within the grounds of ZSL  See image here

IMAGE - July 2013 - An image was posted on the website of Anthony von Plettenberg Laing of Aesculapian Snakes within the grounds of ZSL  See image here

VIDEO - 2013 an Aesculapian Snake was seen basking along the edge of Regent's Canal by members of the public. It was filmed and shared on YouTube. 
See the video here:  Aesculapian Snake on YouTube

VIDEO - 16th May 2006 - The BBC program "IOLO's Welsh Safari" had a feature showing footage of Aesculapian Snakes living wild around the grounds of the Welsh Mountain Zoo. The first time these snakes had been caught on film. See article here


VIDEO - February 2020 - Using my web page on Aesculapian Snakes as research material Jack Perks, known for his incredible underwater photography, produced a short YouTube film about the Aesculapian Snakes in London, featuring Will Atkins, which was released in February 2020. Sadly the true origin of the feral population of London Aesculapian Snakes was withheld from the film. It was also mistakenly claimed in the film that Aesculapian Snakes have never been kept at London Zoo. Guide books for the Zoological Society of London dating from 1928 to 1935 confirm that Aesculapian Snakes were indeed one of several species kept at London Zoo in an "outdoor Reptile Rock Garden" from at least 1928 to 1935 and possibly as late as the early 1960s when the Reptile Rock Garden ceased to be restocked with European snakes.  

The Aesculapian Snakes in London can be extremely unpredictable and difficult to find and on the day of filming in August 2019 Jack & Will were unfortunately unable to find any wild Aesculapian Snakes at Regent's Canal and were forced to use captive specimens in Staffordshire to feature in the film. The film shows how beautifully docile this species can be. Jack's images can be seen here.

London Aesculapian Snakes in Litriature

The 2016 book by James Lowen, "A Summer Of British Wildlife" makes mention of the London Aesculapian Snakes but fails to give any accurate information on the origin of these non-native snakes, claiming "Nobody knows exactly how these harmless mud-green, European serpents reached London but some fingers point towards the adjacent zoo."

See relevant section, Day 97, page 230 here:  A Summer Of British Wildlife by James Lowen

James Lowen has unfortunately made unfounded claims elsewhere that the London Aesculapian Snake population originated from escapees from London Zoo. See LINK here.


Research on the Welsh Aesculapian Snakes 2020

Worryingly it seems the London Aesculapian Snakes are not the only ones under threat. According to January 2020 Issue 3 Edition of the 'Wales Invasive Non-native Species Group Newsletter' the Colwyn Bay population of Aesculapian Snakes are being radio tagged throughout 2020 & 2021 to help compile data that will be used to build a plan for their control and possible removal from the wild.

"The Biodiversity and Ecosystem Evidence and Research Needs (BEERN) Programme has provided funding under the KESS Studentship scheme for an impact assessment of the introduced Aesculapian Snake population in North Wales.

This project seeks to develop a widely applicable model system for early invasive species assessment and control planning that will benefit invasive species control efforts in the UK. Through the monitoring of their movements and habitats, the data on snake behaviour and habitat use will feed into an integrated removal plan for the species and contribute to preventing further range expansion and invasiveness. The project began in October 2017 and will continue until October 2021. Snakes will be implanted with radio transmitters between April 2020 and September 2020, and again April 2021 until September 2021."  


Have you seen an Aesculapian Snake in London?  Do you have information to share?

It is currently unknown how many of these London Snakes still survive in the wild in London. If you are lucky enough to see one yourself please do get in touch with me as I'd love to hear that they are still clinging on in 2020 despite all odds.

Please submit your records of any London Aesculapian Snake sightings to both myself at: and also Will Atkins at: 

This page on my website was originally written in 2011. It has been updated regularly ever since with new and up to date information constantly being added. If you have any information on Aesculapian Snakes that I could add to my website or you have knowledge of the history or future work at the London or either  of the two Welsh Aesculapian Snake populations then I'd be fascinated to hear from you.

Lastly, I would like to make an appeal  to anyone considering catching and keeping a wild Aesculapian Snake as a pet. PLEASE DON'T!  It is an absolute joy being able to find, photograph and watch these beautiful reptiles living wild and free in the UK. They have found a niche in our ecosystem that has allowed them to flourish without upsetting the delicate balance  of our environment. It was once suspected that there could be a maximum of 20 breeding pairs in the London population but numbers are now believed to be much lower. Just removing one snake could have serious consequences for the future of this species in London. Many of these snakes have already been caught, and with the high number of rodent traps being used in the area, these are also likely to have a negative impact on number of these snakes. Please just be grateful if you are lucky enough to see one, let it live in peace in the wild, and let other people also experience the joy of seeing them living wild in the UK.

Although considered non-native. the Aesculapian Snake has been protected by UK law since it was revised on 16th March 1992, against being harmed or killed under the 1981 Wildlife & Countryside Act.  This law came into effect from 1st January 1993.   See additional link




This website page is the result of many years of research and field work,  all photographs and text on this page are copyright protected by law and are the intellectual property of Jason Steel. Do not use without my written consent.

Photographs were taken using:

 Canon 7D & 40D cameras and the Canon 70-300mm f/4-5.6IS, Canon 100mm f/2.8IS Macro,  Canon 15-85mm and Sigma 14mm f/2.8 Wide-Angle lenses.

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