False Widow Spiders

Unfortunately this week I have been a bit slow on the draw when it comes to posting, but here at last are photos of False Widows to help you identify them. It seems they have been in the south of the country in small numbers for over a century, but with the mild winters of the 1990s and 2000s they spread about the island of Ireland rapidly, aided greatly by the sheer amount of activity of  the Celtic Tiger.

A classic example of a female Steatoda nobilis, the larger of the two common False Widows found in the British Isles. She is very similar to the female Missing-sector Orb-weaver spider, but much larger.
A classic example of a female Steatoda nobilis, the larger of the two common False Widows found in the British Isles. She is very similar to the female Missing-sector Orb-weaver spider, but much larger.

Anyhow, the first thing you need to know is that they get their name because of their resemblance to the true widow spiders, the Lactrodectids, They are identical in size and shape and sometimes in colour, depending on the species.  And, most importantly, they are also venomous to humans, but much less so than the true widow spiders. However, if you have an allergy to their bite then it might as well be a true widow spider, and you immediately need medical help. How do you know if you are allergic? Simple, you will also be allergic to bee stings. The acid in bee stings is almost identical to the acid in the venom of these spiders, and to the acid in nettle stings. Crushed leaves of the Dock plant are very effective at treating all three stings if you are not allergic, as is a little baking soda dissolved in water, as these things are alkalis. If you are allergic or get any sort of large swelling after a bite, whatever the biter was, always seek medical help immediately. Don’t try to tough it out.

A dark female specimen of Steatoda nobilis.
A dark female specimen of Steatoda nobilis.

The female Steatoda nobilis can be very dark, as in the photo above,  but the slightly smaller Steatoda grossa can be as shiny and black as a black currant, and is much more easily confused with the infamous Black Widow. The usual patterns that distinguish the species can often only be seen under a strong light, such as from a flash bulb. False Widows spend almost their entire lives hanging upside down and are very slow-moving. If they are attacked they normally pull their legs in tight to their bodies like a tortoise and drop to the ground to wait until the danger has passed. They mostly get onto humans (a rare enough event) when they are accidentally carried away in items from sheds.

A male Steatoda nobilis trying to convince a female to mate having blocked her retreat into the hollow rung of an upturned ladder. He has very red legs and is as large as she is although his abdomen is much smaller. Pregnant females will have swollen and shiny abdomens about the size of a black currant or a little larger.
A male Steatoda nobilis trying to convince a female to mate having blocked her retreat into the hollow rung of an upturned ladder. He has very red legs and is as large as she is although his abdomen is much smaller. Pregnant females will have swollen and shiny abdomens about the size of a black currant or a little larger.

Unlike true widow spiders, the males of False Widows can be almost as big as the females, and well capable of bullying a female into mating. The true widows don’t stand for that behaviour, which is why they become widows so soon. But their males are much smaller than them. Right now, in Autumn the male Steatoda nobilis spiders are roving around still looking for females. They climb walls outside houses where the females usually wait quietly under the eaves. Some males do get eaten, but this year every male I’ve seen successfully mated and escaped to mate again. That’s probably why they grow as large as their females.

A magnificent example of a male Steatoda grossa False Widow, seen not now but in the spring, their time to wander round. they don't get very big though, but big enough if you don't like spiders.
A magnificent example of a male Steatoda grossa False Widow, seen not now but in the spring, their time to wander round. They don’t get very big though, but big enough if you don’t like spiders.

Although the female Steatoda grossa is very similar in habits to the larger S. nobilis, they much more readily enter houses, particularly sheds and quiet and cool attics. They arrive as tiny spiders and stay put only if they are not disturbed. The male S. grossa is completely different to the female. He seeks her out not in autumn, but in the springtime. Larger ones can resemble the long-legged running House Spiders that terrify people every autumn but they are not nearly so big and can be very brightly coloured. Above is a classic example of a male Steatoda grossa, which prefers running along the ground to climbing around upside down, until he finds a mate. He is clearly built for running.

Now, that mostly takes care of False Widows but I will be uploading a video soon which some people will probably find more useful as the behaviour of various spiders is more obvious.

4 thoughts on “False Widow Spiders”

  1. Hi , I’ve noticed today an infestation of false widows around all the doors and windows of my house, what should I do?

  2. Hi Karen,
    False Widows are very territorial, so it’s unlikely they’re all the one species. They generally stay away from each other. However, the best way is just to regularly run a brush around the windows to clean away the webs. If they can’t put up webs they’ll get tired and move away. It might take a few weeks of regular sweeping before they realise the situation won’t be improving for them. Make sure to clean the brush afterwards if you intend bringing it indoors. Do you have a photo of the spider/spiders? Sam

  3. I’ve got a female possibly pregnant false black widow steatite nobilis in my door way. She appears every night! I thought she was a berry as she is very shiny! Do they habit the same place for years?? Or move on? And do they enter the house in winter? Many thanks…. I’ve got a beautiful photo of her

  4. Can you tell me a bit about their behavior towards humans? Do they bite and if so generally what the effects are? I have found two in my home are different times and was bitten by a spider (unsure of what kind as my home has so many different types) and have been suffering from physical issues so I’m trying to see if it’s the culprit? I have a picture of one of the ones I saw if that would help.

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