What are false widow spiders?
The name false widow is used for several species of spider belonging to the genus Steatoda, part of the cobweb spider family Theridiidae. Around 120 Steatoda species are recognised worldwide, but only three are commonly found in Ireland and the UK.
These are the noble false widow (Steatoda nobilis), cupboard spider (Steatoda grossa) and rabbit hutch spider (Steatoda bipunctata).
The noble false widow is the best known of the three and is the species responsible for most documented medically significant false-widow bites in Ireland and Britain.
False widow vs black widow
False widow spiders (Steatoda) and true widow spiders (Latrodectus) belong to the same family, Theridiidae. This relationship helps explain some of their similarities, including their rounded abdomens and the irregular tangle webs they construct. Despite the name, however, false widows are not black widows and belong to a separate genus.
What does a false widow look like?
False widows are typically brown, reddish-brown or very dark brown, although colour varies considerably between species and individuals. Many have pale cream or beige markings on the abdomen, but these can become faint or almost disappear in some mature spiders.
Their abdomen is generally rounded and can appear particularly bulbous in adult females. The exact shape, colouring and markings differ between the three Steatoda species commonly found in Ireland and Britain, so no single marking should be relied upon for identification.
What does a black widow look like?
Black widows belong to the genus Latrodectus. Adult females of several well-known species have a glossy black body with a distinctive red or orange hourglass-shaped marking on the underside of the abdomen, although appearance varies between species and life stages.
True black widows are not established as commonly occurring spiders in Ireland, so finding a dark spider with a rounded abdomen in an Irish home does not mean that it is a black widow.
Are false widows as dangerous as black widows?
The medical effects of spider bites vary, and suspected bites cannot usually be identified reliably from the appearance of a skin lesion alone.
For detailed information about symptoms, documented cases and what to do following a suspected bite, see our guide to false widow spider bites.
Three false widow species found in Ireland and the UK
How do the three false widow species differ?
All belong to the genus Steatoda, but they differ in size, appearance and the places in which they are typically found.
The largest and best-known of the three species. Adult females have a rounded, bulbous abdomen and variable cream markings on a brown to very dark brown background. Males are smaller and much more slender, often with clearer abdominal markings.
The cupboard spider is generally dark brown to almost black, particularly in mature females. Abdominal markings may be faint or absent, which can make older females appear more uniformly dark than noble false widows.
The rabbit hutch spider is the smallest of Ireland’s three false widow species. It is commonly associated with sheds, outbuildings and other sheltered locations and is generally less conspicuous than the noble false widow.
How to identify a false widow spider
Many false widows show pale cream or beige markings on the abdomen, but the pattern differs between species and individuals and may become less distinct as a spider matures. For this reason, the familiar pale or “skull-like” pattern sometimes associated with the noble false widow should never be used as the only identification feature.
Adult females are generally larger and more rounded, while adult males tend to be smaller and more slender with proportionally longer legs. The differences are most useful when considered within an individual species, because a male noble false widow, for example, can look quite different from a mature female cupboard spider.
The spider’s size, web and location provide additional clues. False widows build irregular three-dimensional tangle webs, usually in sheltered positions where the silk is unlikely to be repeatedly disturbed.
Several other spiders found in Ireland and Britain can resemble false widows. If you’re unsure, compare your spider with our false widow lookalikes guide.
Adult female noble false widow spider with distinct markings.
“At the NUI Galway Venom Systems Lab, we have been studying this spider for the past five years and we are finally learning the truth about the false widow story.”
For further reading, our research and sources page brings together peer-reviewed studies and specialist resources covering false widow spiders in Ireland and the UK.
How big are false widow spiders?
False widow spiders are relatively small spiders, although their rounded abdomens and the span of their legs can make them appear considerably larger. Body length is measured without including the legs, which is important when comparing measurements.
Size varies by both species and sex, with females generally larger and more heavily built than males. Of the three false widow species commonly found in Ireland and Britain, the noble false widow is the largest, while the rabbit hutch spider is usually the smallest.
| Species | Adult female body length | Adult male body length |
|---|---|---|
| Noble false widow (Steatoda nobilis) | 8.5–14 mm | 7–10 mm |
| Cupboard spider (Steatoda grossa) | 5–10 mm | 4–6 mm |
| Rabbit hutch spider (Steatoda bipunctata) | 4.5–7 mm | 4–5 mm |
The noble false widow can be noticeably larger than the other two species, particularly when comparing mature females. A large female S. nobilis may reach around 14 mm in body length, while an adult female rabbit hutch spider rarely exceeds around 7 mm.
For a more detailed explanation of male, female and juvenile S. nobilis, see our noble false widow identification guide.
What does a false widow spider web look like?
False widow spiders build irregular three-dimensional tangle webs, sometimes loosely described as cobwebs. Unlike the symmetrical circular webs created by orb-weaving spiders, false widow webs consist of an apparently disordered network of silk attached to surrounding surfaces.
The web commonly includes sticky capture threads that help trap insects moving through or beneath it. Vibrations travel through the silk to the spider, which usually remains in or close to a sheltered retreat connected to the web.
Around buildings, false widow webs may be found near window and door frames, sheds, garages, fences, wall crevices and other protected corners. Well-established webs can become relatively dense and may incorporate a retreat leading into a crack or sheltered space.
Web structure is a valuable identification clue, but an irregular tangle web alone does not prove that a false widow is present. Other cobweb spiders can construct superficially similar webs, so the spider itself should also be examined.
For comparisons with orb webs, lace webs and sheet-and-funnel webs, see our guide to spider webs in Ireland.
If false widows or other spiders are regularly appearing around your home, see our practical guide to reducing the number that find their way indoors.
