Aesculapian Snakes in London

Last Updated: 2nd August 2019

Inner-city Serpent - 3.5ft adult female Aesculapian Snake 2016

Aesculapian Rat Snake  (Zamenis longissimus, previously Elaphe longissima)

Here in the UK we have three native snake species and one non-native snake that has established healthy breeding colonies at two 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 Snake, and is only found in two 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. One is in Central London, England and the other is in Colwyn Bay, Wales. The nearest population of wild Aesculapian Snakes outside of the UK are in NW France.

These long slender snakes, of the Colubridae family, are Old World Snakes and one of Europe's longest. They regularly grow to a length of 140-160cm. In warmer parts of Europe they reach up to 180cm and have even reached 225cm on one occasion. This makes them the longest snake found in the UK, and one of the longest in Europe. The maximum weight for males is 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 semi-arboreal meaning that they are excellent climbers and 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 two separate populations of Aesculapian Snakes end up here in the UK? 

Welsh population of Aesculapian Snakes

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 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. 

London population of Aesculapian Snakes

By 2018 the London population of Aesculapians had 50 different adult specimens recorded by Will Atkins and in 2013 this population was then estimated at around 40 specimens. However numbers of Aesculapian Snake seem to have fallen significantly in London over recent years. And in 2019 it is now uncertain how many of this once thriving population of snakes now survive. 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 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 adjacent to London Zoo rented by ILEA (Inner London Education Authority facility for scientific experiments) along Regent's Canal. In 2010 David Bird, a former zoo curator, told the Camden Review reporter 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.

Christopher Lever discussed the London Aesculapians in his 2009 book, and Will Atkins & Tom Langton went into more detail when they wrote an account in The London Naturalist No.90, 2011 on page 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.”

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 is no. Following ongoing studies of both the Aesculapian Snake populations in the UK by leading 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 member of the public.

These snakes also seem dependant 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 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 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 the 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 do so again if they could reach our southern shores.

Adult female Aesculapian Snake

Are these snakes dangerous?

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

Adult female Aesculapian Snake by Regent's Canal, London

Adult female Aesculapian Snake

Adult female Aesculapian Snake

Unlike all the other snake species found in Britain, it is the male Aesculapian Snake that is usually larger 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

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 has been 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 of 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. 

Adult male Aesculapian Snake

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

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. 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. 

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. 

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 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.

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:  

"This snake was found on the canal's edge, mosaic-basking amidst grass and twigs on the ground. Only a few inches of the scales on the middle of the snake's 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 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."

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, believes this "suggests that there are anticoagulant enzymes at work" from the Aesculapian Snake's saliva.

Read the paper by W & F Hayes here.

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 scaremongering stories were full of false information and inaccurate reports with ridiculous claims and headlines including: "KILLER snakes that are capable of crushing small children to death are on the loose in Britain! "

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 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 released the following statement claiming that they have 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.

Adult male Aesculapian Snake

Rather than attempting to remove the snakes from London the action that appeared to have been taken in 2016 was to lay high numbers of rodent 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 harder for them to survive.  It's possible that that some snakes could have been killed by feeding on poisoned rodents. 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 deployed in the area seems to have been reduced. 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 July 2019. The last sighting was by by Andi Roy.

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 in May 2017 - inaturalist.org

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

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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 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). 

There is also 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 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 this hypothesis is unlikely.

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

This map shows the range in 2016 for Aesculapian Snakes across Europe. See detailed ICUN Red List map here.  See 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. 

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.

Where can I find wild Aesculapian Snakes?

Inaturalist.org shows records of sightings across Europe including some from both Wales and London.  inaturalist.org

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

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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. There are suspected to be a maximum of 20 breeding pairs in the London population. Just removing one snake could have serious consequences for the future of this species in the UK. Many of these snakes have already been caught, and with the increasing 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

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All Photographs and text on this page are copyright protected and are the intellectual property of Jason Steel. Photographs were taken using:

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