What Do Widow Spiders Look Like?
Spider younglings are often hard to distinguish from other spider species. Most adult female widow spiders have a glossy-jet black coloration, a red or orange hourglass, or similar such marking on the underside. They are about the size of a ½ dollar coin spin a “sticky,” irregularly shaped web.
Red widow (Latrodectus bishop)
Adult female red widow spiders are reddish-orange, with reddish colored legs and a black or dark colored abdomen. The top of the abdomen usually has rows of red or orange spots outlined in white or yellow. Females lack a complete hourglass shape on the underside of the abdomen. Instead, they usually have one or two small red marks that look somewhat triangular.
What is the difference between a black widow spider and a false widow spider?
False Black Widows (Steatoda grossa)
This spider does not have the red hourglass marking and is a glossy chocolate brown colored spider. It shares the same rounded-abdomen body form and web-making traits as the true black widow spiders. However, this spider is slightly smaller than a mature western black widow spider. False black widows can bite if picked up or otherwise touched, but its bite is rare and is not considered a medically important spider.
Statistics
Size: usually up to 14mm (10mm in males) body length, with a leg span that covers a fifty pence piece.
When to see
Throughout the year, but most often seen between July and November.
Black Widow vs False Widow
I was told by a professor that black widows hang upside down on the web and false widows do not. For reference this college was in Indiana and the professor was not an entomologist.
A few years later I visited the Audubon insectarium and I asked someone in the spider area about this fact. They didn’t know, but checked in the back and oddly said all the false widows they had were not hanging upside down. They didn’t have any black widows at the time.Can anyone confirm this? I’m also curious if false widows mimic black widows but don’t instinctively display their hourglass pattern.
Some more on the differences. Widows(Latrodectus) and false widows(Steatoda) both tend to have distinctive patterns on their abdomen and some banding on their legs as immature spiders. With the exception of a few species though, s. paykulliana, the patterns they show are very easy to differentiate the two genera. Females of both genera tend to darken over time which leads to the confusion in identifying them. Most steatoda sp. are also significantly smaller than latrodectus sp. No steatoda that I am aware of have vibrant hourglasses, but it should be noted that not all latrodectus spiders will keep the complete hourglass, or have it at all. It’s also possible for the Hourglass to be colors other than red, like what we see in brown widows. Morphologically there are differences in the shape of their abdomen and leg proportions. Their eyes are also different, but good luck getting a close look at those, they are tiny. Steatoda abdomen tend to be more flat and oval-shaped, while latrodectus are more globe shaped and come to a point near the spinerrets. I like to think of them as tear or watter-drop shaped. Latrodectus legs, especially the first pair, are much longer and have different proportions, and the terminal segment(metatarsus) is much smaller than the one preceeding it(tibia), while steatodas are more tapered and more close in proportions.
Mature female latrodectus are the only ones recognized to be medically significant, but larger mature female steatoda can still bite and afflict a similar but much less severe illness. Latrodectism and steatodism share almost the same symptom profile, but with latrodectism being significantly worse. That said, in the majority of bites from both spiders, symptoms remain local to the bite area. There is also some interesting variability in latrodectus venom potency and yield. For example, the southern black widow has a less potent per unit venom than the brown widow in laboratory tests on mice, however I’m recorded bites on humans, brown widow bites have always been minor in comparison to the black widows found in much of the world, likely due to a much smaller venom yield. The dose makes the poison, as they say. As it stands, brown widows don’t have the evidence to support being medically significant, while there is sufficient evidence for black widows being dangerous. That said, no one has died from a North American widow in a very long time, and reports of deaths due to them in older news and literature don’t stand up to the scientific rigor of today. It is possible, in the right circumstances that a full envenomation could kill someone young, old, or infirm, but I highly doubt a healthy adult would.
About
There are three very similar species of false widow spider that are likely to be found in or around our homes: Steatoda bipunctata (known as the rabbit hutch spider), Steatoda grossa (known as the cupboard spider) and Steatoda nobilis (known as the noble false widow).
The noble false widow is the largest of these three species, with males typically growing to body lengths of up to 10mm and females up to 14mm. Noble false widows are not native to the UK, but are thought to have arrived from the Canary Islands in banana boxes in the late 1800s. Populations became established along the south coast and have since spread north, likely aided in their expansion by global warming. The other two species are both native to the UK.
False widow spiders often appear in news stories about spider bites, typically in early autumn. However, confirmed cases of false widow bites are rare. Only the two larger species of false widow, the cupboard spider and the noble false widow, are likely to be able to bite through human skin at all. The spiders are not aggressive towards people, and generally don’t bite unless roughly handled; most recorded bites occur because of people accidentally touching a spider which then reacts defensively.
In the extremely rare confirmed cases where a noble false widow has bitten someone, the bite has been compared to a wasp sting. In even rarer cases, the bite may cause a person to feel unwell for a short time.
If you think you have been bitten and you are concerned about the bite, you can find guidance on the NHS website: www.nhs.uk/conditions/insect-bites-and-stings
How to identify
Noble false widows are the largest of the three false widow species likely to be found near homes. The front section of their body is dark brown, as are the legs. The abdomen (the large, oval-shaped rear part of the body) can be variable, with patterns of cream and dark brown marks (sometimes described as skull-shaped) though often with very few markings at all.
Spiders can be difficult to identify and many of the claims of false widow spiders often relate to a different species altogether.
