William Fraser, 14, was asleep in bed when he was woken by a burning sensation in his arm. He went to school the next day as normal, but by the time he got home the pain had worsened and he had blisters. His parents gave him antihistamine and paracetamol and put him to bed. By Sunday he felt even worse and was taken to hospital where he was treated with antibiotics and allowed home. He is now recovering.

Fraser is the latest victim of one of the UK's growing population of Steatoda nobilis - the flesh-eating false widow, a cousin of the more venomous black widow.

In another Sutton attack, Alexander Giordano, 39, was bitten on the shoulder and wrist. Giordano, who had leukaemia as a child and so has a weakened immune system, was taken to the accident and emergency department of his local hospital, where he was given a course of antihistamines, antibiotics and cream for the infected areas.

Recently Steve Harris, 22, an amateur footballer in Dawlish, Devon, was forced to undergo emergency surgery after being bitten by a suspected false widow, and a mum in Hirwaun near Aberdare, south Wales, stumbled across a nest of "50" false widows in her garden. In Essex Ricki Whitmore, 39, almost lost a leg after being bitten when he disturbed a nest while decorating a school classroom.

This year there has been an increase in sightings - or suspected sightings - of the spider, which has been in the UK for over 100 years since arriving from the Canary Islands. The spiders have shiny black flesh, bulbous bodies, skull-like patterns on their backs and thick legs. Only the females bite.

Symptoms of a false widow bite are normally no more serious than a bee sting, with a burning sensation and swelling, but in some circumstances a bite can induce nausea and unconsciousness. No one has died from a false widow attack, but people are advised to treat bites to prevent them getting infected.

Experts stress that false widows only attack when threatened or disturbed and dismiss suggestions that a warming climate may be to blame for the increase in sightings in the UK, pointing out that last winter's unusually mild temperatures were followed by one of the coldest Marches in memory.