An urgent warning has been issued across parts of the UK following a rise in sightings of adders, the country’s only native venomous snake. The public is being advised to remain alert, particularly in areas where the snakes are known to reside, including London.
The increase in sightings in 2025 has been noted in regions such as southern England, Cornwall and Wales. In response, local police forces and wildlife organisations have issued statements urging caution, especially when walking in areas with tall grass or natural habitats.
The adder, also known as the common European viper, has long been part of Britain’s wildlife and is not a new arrival. These snakes are typically elusive and tend to avoid human contact, but they are venomous and may bite if provoked or startled.
According to The Wildlife Trust, “The adder is the UK’s only venomous snake but its venom is generally of little danger to humans. An adder bite can be painful and cause inflammation, but is really only dangerous to the very young, ill or old.”
Although fatalities are extremely rare, medical attention is advised in the event of a bite. Adders are most commonly active during warmer months and are often seen basking in sunlight in open areas such as grassy fields or heathland.
Dog owners are also being urged to take precautions, as adders may pose a risk to pets. While the snakes do not typically approach animals, they may bite if surprised. It is recommended to keep dogs on a lead in areas where adders may be present and to avoid letting them roam into undergrowth or long grass.
London is not exempt from this warning. A study conducted by English Nature for the London Biodiversity Partnership’s Reptiles Species Action Plan confirmed the presence of adders within Greater London. Although the population in the capital is relatively small, sightings have been reported in woodland edges, grasslands, heathlands, and some brownfield sites—habitats where the snakes hunt their preferred rodent prey.
While it is unlikely that adders will be found in urban gardens, they may be spotted in larger parks or natural reserves. Londoners are advised to remain cautious while enjoying outdoor spaces and to avoid disturbing wildlife.
Adders can live up to 15 years and grow up to 80 centimetres in length. They are protected under UK law, making it illegal to kill, harm or sell them.
