A female adder, Vipera berus (Photo by AlexandreRoux01, used under Creative Commons licence CC-SA-1.0).


In this post we profile the common vipers (aka adders) living in London, UK and discuss outcomes of a successful reintroduction project, including insights from a visit by WPC’s Lead Biologist, Jonathan Choquette.


The common viper, or adder (Vipera berus), is an elusive and fascinating creature. Adders are medium-sized venomous snakes which are easily identified by a zig-zag stripe down their backs. Somewhat unique among snakes, males and females are coloured differently: males are generally grey with a black stripe, while females are generally light brown with a dark brown stripe. They are heavy-bodied snakes but adults don’t get much longer than about 60 cm.

Adders will generally hunt and eat small mammals, amphibians and lizards, and they prefer to inhabit mid-successional vegetation communities, including heathland, grassland, and moorland. This snake’s range extends throughout Eastern and Central Europe, stretching east into northern China, and north past the Arctic Circle! The UK represents the north-western extreme of the adder’s range

V. berus has faced centuries of human prosecution, habitat loss and habitat fragmentation across its range. In the UK, Adders are now recognized as a species in need of conservation. Adders, along with all British reptiles, are protected under the Wildlife and Countryside Act of 1981, which prohibits the capture, harm, or killing of these animals. It is believed that V. berus was once widespread but has declined across much of England due to deliberate killings and loss and degradation of habitat throughout the past century.

A view of the London skyline from the ArcelorMittal Orbit, the UK’s tallest sculpture. The City Mill River is seen flowing in the foreground, while the skyscrapers of the Canary Wharf district rise in the background. Photo: J. Choquette


Despite its highly urbanized surroundings, there are a small number of sites remaining in the Greater London Area that continue to support populations of adders. One such site is Hounslow Heath, located in West London, which is an unexpected refuge for the elusive adder. Open grasslands, pockets of woodland, and areas of scrub provide an ideal mix of vegetation, supporting not only adders, but many rare plants, insects, birds and other reptiles.

Hounslow Heath once covered a vast area of over 1725 ha, but a mere 82 ha remain. The heath remnants were declared a Local Nature Reserve in 1991, and conservation efforts such as active habitat restoration works were initiated thereafter, specifically targeting the rare heath vegetation community and promoting suitable adder habitat. As a result, Hounslow Heath was later deemed a suitable site for adder reintroduction.

The rare heathland vegetation community at Hounslow Heath. Despite the wild character of this landscape, people are never too far from view. The proximity to Heathrow Airport means a jumbo jet thunders overhead once every 2 minutes. Photo: J. Choquette


Historic knowledge of exact locations where these animals lived is limited, so it can be difficult to determine which sites have had healthy adder populations in the past. Regardless, there was some indication that adders historically occupied the Hounslow Heath area, but become extirpated in the twentieth century possibly due to previous sand and gravel extraction. A survey undertaken prior to reintroduction failed to find any evidence of adders, though the three other species of reptile native to London were found.

In the spring of the year 2000, 46 adders were rescued from a nearby development site and translocated to Hounslow Heath. The released snakes included adult males, adult females, and juveniles, and several of the females were pregnant. Adders were released on two separate occasions into suitable refugia (log pile and mammal burrows). Although this was technically a mitigation translocation from a site slated for development, the project also aimed to reintroduce the species to a nearby site in an effort to ensure its long-term persistence locally. Hounslow Heath was chosen as the receptor site for many reasons: safety from development as a nature reserve, appropriate size and type of habitat for adders, good partnerships with site managers, and its proximity to the donor site.

London United Tramways map, circa. 1910, showing that Hounslow Heath has been accessible from the heart of London via public transit for over 110 years. Access via electric tramway (red line) has since been replaced by London Transit’s red double-decker busses, and the nearest London Underground station (blue line) is now called Hounslow Central (Map courtesy of London Transport Museum: ltmuseum.co.uk.  Photo: J. Choquette


In the early years after reintroduction, adders appeared to have established themselves at Hounslow Heath, and were found using habitats away from the vicinity of the original release site to forage during summer. A string of major wildfires at the site in 2003 led to the confirmed death of at least three adders, but surprisingly, the species held on; at least 8 animals were observed during spring emergence the following year. Despite a lack of systematic monitoring, adders have been observed almost annually since the initial releases, and reproduction has been confirmed.

In 2016, a number of gravid females were found and the adder population was thought to have grown to over four times the size of the reintroduced population, with a diverse age structure. Adders now occupy nearly all parts of the Heath. As of spring 2023, its been a full 23 years since the initial reintroduction, which is equivalent to about 4 adder generations. Therefore, more than enough time has passed since the initial releases for the offspring of those individuals to have matured and reproduced. This is a clear indication that a population of adders has been successfully reestablished at Hounslow Heath. Whether adders persist in the long term, however, will depend as much on their genetic variability, as on the altruism of Londoners.

Informational signage posted at Hounslow Heath notifying park users of the presence of Adders. Signs such as these can increase awareness of venomous snakes, thereby contributing toward mitigation of human–snake conflict. Photo by J. Choquette


Adders possess a distinct set of behaviours that facilitate their coexistence with humans. They are relatively shy, preferring to avoid confrontation, and are most active during spring and autumn, when human activity at Hounslow Heath is relatively low. Despite the rarity of negative encounters at the Heath, there was a high-profile case of a snakebite in 2017 which was reported by multiple news outlets, painting a somewhat negative view of adder presence in the park. This incident spurred the installation of informational signage, an interpretive centre, and a Hounslow Heath reptile walk and Conservation Day to raise public awareness and increase participation in adder conservation.

Although reintroductions of a venomous species can be controversial, education has been playing a crucial role in dispelling myths and misunderstandings about adders, and visitors are reported to be remarkably accepting of the adder population at Hounslow Heath. The adders seem to have benefited from restricted public access on parts of the heath and from an encouraged sense of public responsibility for the snakes. Continued research, public support, and collaboration between conservation organizations and the local community will increase the likelihood that adders persist in the long-term, securing a brighter future for these fascinating snakes in their urban habitat.

While challenges such as habitat fragmentation, succession, and human disturbance persist, the adders of Hounslow Heath serve as a testament to the resilience of wildlife in the face of urbanization. By understanding their behaviour, promoting tolerance, and actively conserving their habitat, we can ensure the survival of these remarkable creatures. The story of Hounslow Heath is an example of how humans and venomous snakes can co-exist, creating a balance between urban life and the natural world.

A snake in the grass. If you are lucky enough to catch a glimpse of a wild adder, well … a glimpse is all you are likely to catch before it slithers off into the undergrowth. Adders are a shy and secretive snake and prefer to scamper than to pick a fight. Photo: J. Choquette


“Hounslow Heath represents a good example of what can be achieved when a local community takes pride in its adders.”


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Atkins, W. 2005. Conservation Status of the Adder Vipera berus in Greater London.  English Nature Research Report 666. English Nature, London, UK.

Foster, J. 2016. Strategic challenges and solutions for adder conservation. Amphibian and Reptile Conservation, Witley Centre, Witley, Surrey, UK.

Matthes, G. 2016. Adder Translocation Case-study, Hounslow Heath. GPM Ecology, Surrey, UK.

Milton, N. 2022. The Secret Life of the Adder: The Vanishing Viper. White Owl, South Yorkshire, UK.

Slack, C. 2016. Management on Hounslow Heath LNR 2000 to 2016: A description of site management on Hounslow Heath Local Nature Reserve from the translocation of adders on to the site in 2000 through to the present day. Carillion Plc, Wolverhampton, UK.

Worthington-Hill, J. 2016. Reintroduction of the adder Vipera berus to Nottinghamshire: a feasibility study. People’s Trust for Endangered Species, London, UK.

Authorship note: This blog post was written by Natasha Sawatzky and Jonathan Choquette.

WPC appreciates funding support provided by the Ontario Ministry of Environment, Conservation and Parks’ Species at Risk Stewardship Program for WPC’s Ojibway Reptile Recovery Program.