How many UK spiders are actually dangerous?
Finding a baby Aragog in your house can be terrifying - but are there any species in the UK that could actually do us harm?
We are lucky in the UK. Unlike many parts of the world, there are very few animals here that can do us any harm. That said, there are a few species that need to be 'handled with care'. Most of these are invertebrates, the obvious candidates being wasps and bees. There are also a handful of UK spider species that can give us a nip. There is a big difference though between an animal being able to bite, and us needing to think of the animal as 'dangerous'.
There are around 650 species of spider in the UK, ranging from those with a leg span of just a couple of millimetres, to the 12cm leg span of the cardinal spider. Spiders are predators, and they use an impressive pair of fangs to catch prey, and to introduce venom. All spiders have fangs but not all spiders have fangs that are able to pierce human skin. Consequently, there are relatively few UK species that are able to bite us in any meaningful way.
According to the Natural History Museum, there are just 12 species of spider that have been known to bite people. These include some quite common spiders we might find around our homes and gardens, including the woodlouse spiders and the so-called house spiders we see moving around in autumn. Bites from these spiders are extremely uncommon because, like most spiders, they are not aggressive. Even if you were unlucky enough to get bitten it is extremely unlikely that the bite would develop into anything more than short-lived, low-level pain. Some spider species have venoms that might also cause some localised swelling or itching.
The venom from most of the handful of UK species that can bite is less concerning than the puncture wound the bite causes. Fangs can introduce bacteria into the tiny wounds they create, so if you suspect you have been bitten by a spider it is best to clean the wound and use a local antiseptic treatment. Just as with a wasp or bee sting, antihistamines may help with the swelling and itching but if symptoms do not improve, get worse or develop into other symptoms then it is sensible to seek medical attention. Rarely, some people may be allergic to spider venom, with similar symptoms developing as with a bee or wasp sting allergy.
One spider that recent research suggests may be of some medical concern is the noble false widow spider Steatoda nobilis. This species was first recorded in the UK in Torquay in 1879 and has recently increased in abundance and range. The media have been quick to pick up on 'spider bite' stories, but it often not possible to verify that the victim has been bitten by any spider, let alone a noble false widow. Nonetheless, this species can bite and, because it seems to thrive in urban areas and around our homes and outbuildings, then we might expect to see more reports of bites as time goes on.
For most, the bite from a noble false widow, is nothing more than a short-lived, nuisance, rather like a bee or wasp sting. For a very few people, a bite might develop into something more serious. A study in Ireland of confirmed false widow bites found that some required hospitalisation but this should not be cause for panic. Amongst the scaremongering we should always remember that spider bites are incredibly rare in the UK. The vast majority of us will never get bitten by a spider, and of those few that do, the vast majority will experience only very minor effects.
- How big would a spider have to be before it is unable to stick to the wall?
- Why don’t spiders bleed to death if they lose a leg?
- Why don’t spiders get caught in their own web?
- Are there any vegetarian spiders?
To submit your questions email us at questions@(don’t forget to include your name and location)
Adam Hart is an entomologist and Professor of Science Communication at the University of Gloucestershire. As well as research and teaching, he is a regular broadcaster for BBC Radio 4 and the BBC World Service, presenting documentaries on topics from trophy hunting to tree diseases. He has also presented the weekly science program Science in Action for the BBC World Service. On television, Adam has co-presented several documentary series, most notably BBC4’s Planet Ant and BBC2’s Hive Alive.