If you believe the national tabloids, every autumn our UK homes are invaded by these highly venomous arachnids. But are these spiders really as menacing as their infamous, black widow cousins?
How do I identify a false widow spider?
In the UK, false widow spiders form a group of six species known as Steatoda spp. The three most common types are the noble false widow (Steatoda nobilis), the rabbit hutch spider (Steatoda bipunctata) and the cupboard spider (Steatoda grossa). The headline-grabbing noble false widow, however, isn’t native to this country, reputedly having arrived by banana boxes from the Canary Islands in the 19th Century.
As the largest of the three, the noble false widow has a body length of between 10mm and 14mm, and it has a distinctive set of markings on its abdomen, which can resemble a skull. These marks can completely vary, or can even be non-existent, especially in adult females.
False widows will usually have a narrow white or slightly lighter band towards their head. While females have a globular shiny abdomen, the male abdomens are smaller and less rounded. The native rabbit hutch spider and cupboard spider are smaller than the noble false widow, around 5-7mm and 10mm respectively.
Are false widows dangerous in the UK?
The British Arachnological Society points out that “bites by false widows are difficult to substantiate and often highly exaggerated by the media”.
There have been some headline-grabbing stories in the UK press ‘warning’ of noble false widow bites, but these need to be kept in perspective, given that the symptoms of a bite – including the level of pain – are comparable to a nasty wasp sting.
Just one spider bite, however, can attract tabloid headlines, like the recent example of a 15-week baby being bitten in Ireland, who needed to be taken to A&E. With paracetamol the symptoms eased after 12 hours.
In the UK, according to the Natural History Museum, out of 650 species of spiders, there are 12 that can bite humans. Noble false widows get the most attention.
They have fangs that are capable of penetrating human skin, but these bites are rare. If someone is bitten, there can be complications in a small number of cases, if there is an allergic reaction or an infection.
How venomous are false widows?
The tabloids often circulate the findings from a recent study in Ireland that discovered that noble false widow spiders are 230 times more venomous than the average spider in an Irish home. And Dr John Dunbar, from NUI Galway and co-senior author of the study, has said: “The tiniest amounts of venom – about 1,000th of a raindrop – can cause medically significant symptoms in humans that are about 250,000 times larger than them.”
Despite these impressive and attention-grabbing stats, the net effect of the venom of a false widow is still not particularly potent. Usually, the only symptom in humans is pain or swelling around the bite, which may radiate outwards, and it usually lasts from between one and 12 hours, but rarely for more than 24 hours.
Where do false widows live?
You can recognise the webs of false widow spiders as a tangle of criss-cross scaffold threads, which may become dense in the centre. Noble false widows are found in houses and their numbers have been reported as increasing across the country in recent decades.
Having originated in the Canary Islands, they are probably enjoying Britain’s recent spells of warmer weather! In contrast, as their names suggests, the native rabbit hutch spider is found mostly in outdoor animal enclosures or sheds, while the cupboard spider favours storage areas and spots under furniture.
How do I know if I’ve been bitten by a false widow?
This is a good question, as the symptoms are very similar to those of a wasp sting, so it helps if you have actually seen that the culprit is definitely a spider. Also, remember the NHS advice that spider bites in the UK are uncommon. While most false widow bites resemble a nasty wasp sting, a minority of those who have been bitten have described the symptoms as a throbbing pain, with swelling in the affected area and a tingling in the fingers. Dizziness, sickness and sweating can also occur.
Begin by looking for evidence of puncture marks in the skin, which could be painful to touch. If you are bitten by a spider and the symptoms cause concern, medical advice should be sought.
How likely am I to be bitten?
False widows are mainly sedentary and, according to the British Arachnological Society, “being bitten by a spider is very unlikely in this country in normal circumstances”. False widow bites, when they happen, generally occur when someone has accidentally come into close contact by sitting or lying on one of these spiders.
Male false widows are more prone to biting, but this is only because they leave the nest in search of a mate. As mentioned, they are only known to bite when provoked or trapped against skin.
Are false widows related to black widows?
Because of the name and the fact they look similar, false widow spiders (Steatoda spp.) are sometimes confused with black widows (Latrodectus spp.) and are even mistakenly thought to be as dangerous. But while both have a similar dark-coloured, globular body, the similarities stop there.
A comparative study carried out by toxin scientists in Ireland, which looked at the venom of false widows compared to true black widows, discovered that out of a total of 140 toxins found in the false widow, 111 were also found in the black widow. This may sound scary, but the reality is that our UK false widows are nothing like as harmful as their infamous cousins. For example, when it comes to venom a true black widow is in a different league, particularly a large female, as its venom is 15 times more powerful than that of a rattlesnake.
If, in the extremely unlikely case that you do find a widow spider with a distinctive red hourglass colour-marking on its abdomen and black legs, it should ring alarm bells. Any sightings of accidentally imported black widows are extremely rare. In 2012 a mechanic found a pair living in a vintage Ford Falcon car imported from the US, and the spiders in question were rehomed in a zoo.
What is the expert opinion on the media scare stories?
“False widows can bite, and their bite can be painful, but the press coverage makes it seem like bites are very common,” says entomologist and BBC broadcaster Prof Adam Hart.
“The reality is they aren’t. Spiders may not be everyone’s favourite, but they are incredibly important creatures, and we should cherish rather than persecute them.”
About our expert, Adam Hart
Adam is an entonologist and BBC broadcaster. He has presented a number of BBC documenteraries on insects, and written for over 120 scientific papers.