Walkers have been warned not to touch snakes after a spate of venomous adder attacks over the past three years.
There have been around 196 incidents of bites caused by people picking up venomous adders between 2009 and 2011, figures from the Health Protection Agency's National Poisons Information Service (NPIS) showed.
Adders enjoy the warmer weather, and are likely to be more visible in rural areas as the cold-blooded reptiles bask in the sunshine.
In around half the cases reported, a person had picked up an adder believing it be a grass or corn snake. Adders are the only venomous snake living wild in England, Scotland and Wales.
When adder bites deliver venom, it can cause localised pain, tenderness, swelling and bruising which can spread.
If a child is bitten, the effects can be seen across their whole body.
Nine-year-old Tylar Butcher was bitten by an adder in the New Forest in 2011. After a small bite, her whole leg turned black and blue and she was rushed to hospital after a suspected allergic reaction to the venom.
The HPA said almost all poisonings from adder bites produced relatively minor effects, but more serious cases could involve kidney failure in children, abdominal pain, nausea, vomiting, serious heart effects and even - very rarely - death.
Professor Simon Thomas, director of NPIS Newcastle, said: "Adder numbers have decreased in recent years so they are rare but still present in certain areas.
"They usually keep well out of sight, but in the summer months are active because the weather is warmer.
"Because they are well camouflaged, people can accidentally tread on them, which is when they can bite. They can also bite if picked up."
And he said: "The bite can have very nasty effects, especially in smaller children - so it's best to take care when out walking, wear appropriate footwear for the terrain and do not handle any snakes.
"Sometimes the venomous adder can be mistaken for non-venomous species such as the grass snake or smooth snake, making people think it is safe to pick them up."
The way to recognise an adder is from its distinctive zig zag skin and V-shaped marking on its head.
The experts said bites could occur between February and October, most commonly in the warmer summer months.