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Invasion of the false widow spider

Updated on November 12, 2013
False widow spider (Steatoda nobilis) © Chris Leather
False widow spider (Steatoda nobilis) © Chris Leather

Unless you have been living under a rock (or maybe a small crevice) you cannot fail to have heard that the UK is being invaded by a highly venomous relative of the notorious black widow spider. Over the past year I have read stories in both the tabloid and "quality" press about these fearsome arachnids spreading northwards across Britain and attacking all that dare stand in their way. Stories of pets being killed, limbs almost needing to be amputated and schools shut down have all been attributed to the false widow spider.

A few weeks ago I found one of these critters in the utility room of our house. Whilst being mildly arachnophobic I am also very inquisitive and will never kill anything without a good reason. So, I did some research. It didn't take long to become an 'expert' on all things false widow. I use the term expert as given some of the mis-truths and errors in the media's coverage that is what I feel like.

The False Widow Spiders

The false widow spiders are a group of around 120 species that both resemble and are related to the true widow spiders. They belong to the family Steatoda and there are about six species that are now resident in the UK. Most notable of these are Steatoda nobilis (the noble false widow) and to a lesser degree Steatoda grossa (the cupboard spider). Whilst S. grossa is considered a long time native of the UK it is believed that S. nobilis was introduced to Britain in the 1870s with fruit imported from the Canary Islands.

So that's nearly 150 years these spiders have quietly resided here and then suddenly they become public enemy number one within the space of a year or two. One reason for this is there is no doubt the spiders have increased their range. The first spiders are thought to have arrived in Torquay in Devon. It seems that for a long time the spiders remained confined to this area before gaining a foothold in neighbouring regions along the south coast of England.
More recently though false widow spiders have been turning up as far north as the Scottish border. The given explanation seems to be down to climate change with milder weather. There doesn't seem to be any literature covering when the spiders spread across the UK and it is not entirely obvious why the false widow has become this autumn's media bete noire.

Identifying a false widow

The two species of false widow most commonly associated with the name (S. nobilis and S. grossa) are fairly similar in appearance. Often described as around the size of a 50 pence piece, I'd say S. nobilis is slightly bigger than this. With a maximum body length of around 15mm and leg span of up to 35mm these are medium sized spiders by UK standards.

Perhaps their most notable features are the dark, glossy colouration of the legs and thorax and the cream pattern on the large abdomen. This does give them a fleeting resemblance to the black widow spiders.

The webs of these spiders is also a clue. They make a tangled, seemingly random web that is usually positioned quite high up. During the day they hide away in a nearby crack or crevice, coming out at night to hang in their web.

Black widow spider
Black widow spider | Source

Cousin of the black widow spider

As mentioned, the false widow spiders are relatives of the infamous black widow spiders, known for being one of the world's deadliest spiders. The black widows belong to the sub-family Latrodectinae and there are a number of similarities with the false widows (Steatoda).
At a glance both groups have a similar shape; bulbous abdomen and fairly long legs. The colouring of the legs and carapace is similar although the black widows tend to be jett black whereas the false widows are usually a dark brown colour. Both groups may have patterns on the abdomen; S. nobilis has cream markings that are said by some to resemble a skull on the upper side of the abdomen. The classic black widow however, has a red hourglass shape marking on the underside of the abdomen.

It is said that the venom of the black widow spider is 50 times more potent than that of the rattlesnake. That in mind though, I know which I would rather be bitten by (well neither actually, but just for this hub...). Whilst the venom is powerful the spider is small and the fangs can only penetrate 1-2mm. It is still an unpleasant experience even if only very rarely fatal. Symptoms start with intense burning pain at the site of the bite followed by muscle aches around the area. In some cases a systemic condition (Latrodectism) may occur with abdominal cramps, fever and tachycardia all common symptoms.

On the subject of the widow spiders, the name comes from the belief that the female spider would often eat the male as a post-sex snack. Whilst this has been observed in one species in laboratory conditions there is some doubt that this is natural behaviour. All the same...!

The bite

There are around 650 species of spider that can be found in the UK. Of these just over a dozen are capable of inflicting a bite on humans. With considerably more potent venom there is little doubt the false widow (S. nobilis) has the worst bite of all these.

The actual false widow bite is usually described as being on a par with that of a wasp or bee sting. A small pinprick followed by burning pain and local swelling. The venom itself is related to that of the black widow but nowhere near as potent. It has been found that using black widow anti-venom reduces the severity of the bite indicating a close relationship.
The venom of Steatoda spiders is a nuerotoxin - it acts on the nervous system, paralysing small prey. Some spiders have another kind of venom called necrotoxins. Most infamous of these is the brown recluse spider who's bite causes the flesh around the wound to die. Nice!

As with black widow bites there is a systemic condition associated with false widow bites - Steatodism. It seems to consist of a very mild version of Latrodectism with a general feeling of malaise for a day or two.

So why all the hype?

As would be expected the media have picked up on several sensational cases. From what I can see these fall into three categories:

  1. There is an allergic reaction
  2. There is a secondary bacterial infection
  3. There is no proof a false widow was involved

It is a fact that bee stings kill in the region of 10 people a year in the UK. As we all know this isn't because bees carry deadly stings and it would be a stretch to describe the average bee as "death with wings"! It is an allergic reaction to the sting in these cases. So, just as with bee and wasp stings, some people are allergic to spider venom. Even so there still hasn't been a recorded fatality from the bite of a false widow spider.

Amongst the most shocking images of false widow bites was a man who's leg had to be drained after becoming massively infected. Other cases describe limbs nearly needing amputating and victims being given antibiotics.
I'd just like to point out that antibiotics are given to fight bacterial infections and not spider venom. From what I have seen these wounds are classic staph infections - the sort you can pick up from a splinter or going to hospital. Very nasty but not the result of a nuerotoxin.

In one recent newspaper article I remember reading about a woman whose garden had become 'overrun' by false widow spiders. The item went on to show a jar with several dead (harmless) garden spiders in it. This is such lazy journalism; false widows don't even live in gardens, they like it indoors.
Other news stories talk about 'suspected' false widow spiders which 'attacked' the victim. Given how poor people are at recognising these spiders and the fact that the false widow is a runner not a fighter I usually dismiss any story where there isn't a firm ID of the species involved.

Steatoda nobilis - the false widow spider
Steatoda nobilis - the false widow spider | Source

The UK's most dangerous spider?

So, given a few facts about the false widow spider it might be a bit easier to put the threat into context. As a species that has existed in the UK for at least 150 years it is somewhat surprising to find these quite docile spiders elevated to public enemy number one.

But, without any serious competitor for the title I have to admit these are at least the most venomous spiders in the UK and capable of giving the most painful bite of any British spider. Other challengers would include the woodlouse spider which I think should win on looks alone. There is also the lace web weaver spider which can give a little nip - it also has the concerning habit of allowing its young to devour it on hatching. So at least on table manners the false widows do quite well!

In conclusion I would say treat the false widow spider with the respect it deserves. If you are not afraid of spiders then it is fine to ignore them as they will certainly not come looking for trouble. I am happy to have one out in the utility room, however I would not want one in the house where it could possibly come into contact with my children. In this case I would be inclined to carefully remove the spider and relocate it. You can't simply put the spider out of the door as it will probably come back inside. My top tip here would be to put it in someone you don't like's garden!

© 2013 Chris Leather


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