Skip to page content

The truth about false widow spiders

27 May 2007

What's the likelihood of being bitten by a false widow spider? Extremely low.

No one has ever died of a spider bite in the UK and the number of reported bites from spiders in general is minimal. The Natural History Museum's Insect Information Service (IIS) hears of about 10 cases of spider bites each year in the UK.

Every year at about this time Stuart Hine, manager of the IIS, has to deal with enquiries concerning the false widow spiders.

'So far this year we have received over fifty calls from members of the public suspecting this spider in their homes or gardens,' says Stuart.

People also bring in specimens for identification. 'Most turn out to be Steatoda grossa (false widow spider species), though we have received 10 confirmed bite reports from Steatoda nobilis (false widow spider species) over the last 8 years.'

False widow spiders

The false widow spiders belong to the genus, or group, called Steatoda . There are six species of Steatoda found in the UK including one introduced species, Steatoda nobilis .

This group of spiders get their name because they look similar to the true black widow group of spiders, genus Latrodectus .

The false widow spider Steatoda nobilis has a tangled web like other members of the Theridiidae.

The false widow spider Steatoda nobilis has a tangled web like other members of the Theridiidae family of spiders.

Both Steatoda and Latrodectus are in the same family of spiders called Theridiidae . These are the comb-footed spiders that have rows of tiny bristles on the tip of their hind legs they use to spread out their silk. They make similar 'tangle' webs.

Mistaken identity

In the UK two species are commonly mistaken for black widow spiders. They are Steatoda bipunctata, or the rabbit hutch spider, and the one that most resembles the black widow species, Steatoda grossa .

Black widow spiders

Black widow spiders belong to the genus Latrodectus . They have a nasty bite and do occasionally kill. These are found around the world, including southern Europe, southern USA and Mexico, the Middle East and Australia. They are not found in the UK.

The noble false widow (Steatoda nobilis )

One species of false widow spider, Steatoda nobilis , appears to be the UK's most venomous spider.

This species came from the Canary and Madeiran Islands over a 100 years ago. It has been established in Devon for a long time but in recent years has been spreading along the south and east of England and is likely to spread northwards in years to come.

This spider has a brown bulbous abdomen with pale markings and the females grow to 15mm. They live in walls, fences and the barks of trees and eat insects, other invertebrates and even other spiders.

Spider bite symptoms

There are 640 species of spider in the UK. Only 12 of these have been known to bite humans in the UK and this includes two Steatoda species, S. grossa and S. nobilis .

The severity of symptoms from any spider bite depends on the amount of venom that is injected. False widow spider bite reports include symptoms such as chest pains, swelling and tingling of fingers. Last year a man went to hospital for treatment after being bitten by what may have been a false widow spider - the spider was never caught so it wasn't identified.

Climate change

In the UK a succession of mild winters has increased the survival rate of a number of creatures that would more normally die off in cold winters.

'The distribution of the non-native Steatoda nobilis has increased steadily along the south coast over the last 15 years,' says Stuart.

'The native Steatoda grossa has benefited from the same favourable weather and has also noticeably increased in both distribution and frequency. It is now more commonly observed in homes, sheds and garages throughout the south of the UK.'