Inner-city Serpent

The Aesculapian Rat Snake  (Zamenis longissimus)

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 found only in two specific parts of the UK is the non-native Aesculapian Snake. 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 25 years. One is in Central London, England and the other is in Colwyn Bay, Wales. 

These long slender snakes are one of Europe's longest and regularly grow to a length of 140-160cm In warmer parts of Europe they may even reach 225cm. This makes them the longest snake found in the UK. These snakes are usually found across southern, central and eastern Europe and use the same method of incubating their eggs as our native Grass Snakes, using warm damp moist areas of vegetation such as hay piles and compost heaps to provide the necessary heat. Clutch size is usually 5-11 eggs and these may take 6-10 weeks to hatch depending on the weather conditions. 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.

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

The Welsh population of Aesculapian Snakes is estimated at 50+ specimens and came about during the 1960's after a gravid female snake 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. These were first reported by the press during the early '70's.  The London population of Aesculapians had 30 different adult specimens recorded by 2011 and this population was estimated at around 30-40 specimens. However numbers seem to have fallen significantly in London over recent years. It is believed that this population came about after eight snakes were deliberately released in the 1980's from a building close to London Zoo rented by ILEA (Inner London Education Authority facility for scientific experiments) along Regent's Canal. They were first reported in 1998. Will Atkin's & Tom Langton's wrote an account of this 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 colonized 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 euthanased 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."   

Specimens found in London tend to be larger than those in Colwyn Bay and this could be one possible effect of in-breeding by the Welsh snakes, having all derived from a single specimen. These snakes are native to central and eastern Europe and it is believed that the London population originated from Italian specimens, however as yet no DNA testing has been done to confirm this.

Jason Steel photographing a wild Aesculapian Snake along Regents Canal in London, UK. 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 extensive 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.  They also seem dependant on woodland habitat connectivity in order to spread so in 40 years neither of the UK populations of these snakes have been able to spread further than the sites where they are found.

Are these snakes dangerous?

No, not at all. The Aesculapian Snake is non-venomous and not an aggressive species. Unless you're a rodent or a small bird, then you're quite safe.


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 the banks that run parallel to both sides of the canal. 

Aesculapian Snakes get their name from the Greek god Aesculapius, the Greek god of 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. 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. 

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 considerable 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 5-6ft+ in length.


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 appearance has been compared to that of a Twix wrapper.


This adult female specimen exhibits several scars along her body. These may have been caused by attempted predation by birds, foxes, or domestic cats, or by encounters with local council workers using strimmers to cut the grass.


This close-up shot shows the smooth un-keeled scales of adult female Aesculapian Snake number 15, of the London population.


Juvenile Aesculapians sometimes display a yellow collar making them easy to confuse with juvenile Grass Snakes.  Aesculapian Snakes are egg-laying snakes and usually produce clutches of 5 -20 eggs with 5 -15 being common. 

These eggs hatch after 6-10 weeks depending on the weather and incubation temperatures. If they can avoid predation these snakes can generally live for around 25 years and they 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.

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.


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. If handled Aesculapian Snakes may initially bite but usually calm down, 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.


One of two specimens photographed high above the ground basking in the canopy of a large bush.


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.


Some specimens may be very defensive when handled. The bite marks shown above were inflicted by a very defensive adult female Aesculapian Snake. 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.

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 my complete surprise, an angry, wide-mouthed head quickly spun round and latched onto my wrist. Having never experienced any signs of 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 bite 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 harm. 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 bask in the sunshine.

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 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)

Despite these snakes posing little if any threat to our native wildlife (excluding 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". Download the list of "Species of concern in London". Thankfully LISI now seem to be listening 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.

There have been a few discoveries of ancient fossil remains dating back to the warm end of the Pleistocene Period (around 11,700 BC) of Aesculapian Snakes found in Suffolk (B.H.S. Bulletin no.50 1994). So although now considered a non-indigenous species the Aesculapian Snake may have once been native to the UK. This topic is covered in great detail in the 1998 book "Pleistocene Amphibians and Reptiles in Britain and Europe" by Professor J. Alan Holman. 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). 

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

The Aesculapian Snake is one of four species of Rat Snake found in Europe and its range once reached far further north than it does now when the Earth's climate was warmer. This vast range may have been partly due to escaped specimens when the Romans kept Aesculapian Snakes in their temples during the Roman occupation of Europe.

Both albino and melanistic specimens of Aesculapian Snakes have been found in the wild in Austria, Slovenia and Italy but these are incredibly rare. In Greece grey morphs of the Aesculapian Snake can be found.

Although considered non-native. the Aesculapian Snake has been protected by UK law since 1992, against being harmed or killed under the 1981 Wildlife & Countryside Act.

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. In the end they chose to feature Will Atkins (following my recommendation) and I was replaced with the Greek historian, Simon Chaplin. The finished piece was both interesting and informative and portrayed the snakes in a positive light. Watch the video here:    Watch BBC One Show     


Maybe the London population of Aesculapian Snakes did originated 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

This information could make one question whether there is an unlikely possibility that some of the specimens of Aesculapian Snake still found along Regents Canal could indeed have originated from escapees from ZSL?


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.

All Photographs on this page were taken using:

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


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