Short answer
- A false black widow is not a single spider species, and it is not a true black widow. The name is a common name for several spiders in the genus Steatoda, most often the cupboard spider, Steatoda grossa, and the noble false widow, Steatoda nobilis. They look like black widows at a glance because they share a dark, rounded abdomen and a tangled cobweb, but they belong to a different genus from the true black widows, which belong to the genus Latrodectus. The most useful single difference is the marking on the underside of the abdomen. An adult female true black widow typically carries a red or orange hourglass mark there, while a false black widow never carries that bright red hourglass. False black widows are shy spiders of houses, sheds, and sheltered outdoor corners.
What the name “false black widow” really means
The confusion starts with the name itself. It sounds like the name of one animal, but it covers a group of species. The Natural History Museum in London, which runs an identification service for spiders found in the United Kingdom, states that the false widow spiders form a group of species in the genus Steatoda, and that their resemblance to the black widow spiders of the genus Latrodectus is why they cause concern in homes. When one source says the false black widow is dark brown, it may mean Steatoda grossa. When another describes a pale pattern like a skull or a small house on the back, it probably means Steatoda nobilis. When a third describes a pale band down the middle of the abdomen, it may mean Steatoda bipunctata. No single description fits every false widow, because real spiders vary by species, sex, age, and individual.
The word “false” is a human label, not a formal rank. Steatoda and Latrodectus are two genera in the same family, the Theridiidae, commonly called the comb-footed spiders. The family name comes from a comb of serrated bristles on the fourth leg segment of the female, visible with a lens on the largest species, according to the museum identification guide. Sharing a family explains the similar webs and body plan. Belonging to different genera explains why they are not the same spider. Usage also differs by region. In the United States, “false black widow” most often means Steatoda grossa, a common West Coast spider per the University of California, Riverside center. In Britain, “false widow” often means Steatoda nobilis in popular use. This article therefore keeps species names visible throughout.
False black widow compared with a true black widow
| Feature | False black widow (Steatoda) | True black widow (Latrodectus) |
|---|---|---|
| Genus | Steatoda | Latrodectus |
| Underside abdomen mark | No bright red hourglass | Adult female typically has a red or orange hourglass underneath |
| Upper abdomen pattern | Often pale markings on top: crescents, triangles, bands, or a skull-like or house-like shape | Adult female usually plain dark on top, sometimes with red spots |
| Body color | Dark brown, purplish brown, or black, often glossy | Adult female usually shiny black, sometimes very dark brown |
| Size | Females of the best known species measure roughly 4.5 to 14 mm in body length | Adult female western black widow body, excluding legs, measures 5/16 to 5/8 inch, per the University of California IPM program |
| Web | Irregular tangle of threads, often denser in the center | Strong, irregular, tangled cobweb |
| Habitat | Houses, sheds, garages, wall cavities, sheltered corners | Sheltered, dry, undisturbed places such as wood piles, garages, and sheds |
The hourglass is both the best clue and the most misused clue. The University of California IPM program describes the typical adult female black widow as having a shiny black body, slender black legs, and a red or orange hourglass mark on the underside of the large, round abdomen. That mark sits on the belly, so it is not always visible when the spider hangs in its web, and it can vary. Colorado State University Extension notes that in the western widow the hourglass can appear as two unconnected spots, as a roughly rectangular area, or so faint as to be barely visible, and that its color can fade or intensify during the life of an individual spider. The absence of a visible hourglass therefore does not prove a spider is harmless, and pale markings on top do not prove it is a false widow. What can be said with confidence is narrower: a false black widow does not carry the bright red hourglass typical of an adult female true black widow, and its pale markings, when present, sit on the upper side rather than underneath.
Size needs the same caution. False widows are generally smaller than an adult female true black widow, but the ranges overlap, and the noble false widow is about the size of a mature black widow, per the University of California, Riverside account. Body length means the body only, not the legs, and published figures differ slightly because sources measure different populations. Where this article gives a range, it gives the range from the named source and does not average ranges into a new number. Readers who need a firm answer should use a local extension or museum identification service.
What a false black widow looks like in general
Across the group, false widows are small to medium spiders with a rounded, bulbous abdomen that is often shiny, especially in females. Their color runs from dark chocolate brown through purplish brown to near black, and some species have lighter stripes on the legs. The museum identification guide gives a maximum body length of about 15 mm for an adult female across the United Kingdom species, about the size of a small fingernail at most.
The abdomen markings are the most variable part of the animal, and that variability is itself a defining feature. The guide notes that all false widow species have a narrow white or lighter band around the front of the abdomen, but that it can be faded, partial, or missing, especially in adult females. Markings are generally clearer in males and dimmer or absent in females, and younger spiders often show their pattern clearly while older, darker females may lose it almost entirely. A plain dark spider in a cobweb is therefore not automatically a true black widow, and a patterned spider is not automatically a false widow. Females have globular, shiny abdomens, while males have smaller, less rounded, more clearly marked abdomens.
The cupboard spider, Steatoda grossa
Steatoda grossa is the species most readers in the United States mean by “false black widow.” Its common names include the cupboard spider, the dark comb-footed spider, and, in Australia, the brown house spider. The museum guide gives its size as 6.5 to 10 mm for females and 4 to 6 mm for males. Females are usually darker than the noble false widow and the rabbit hutch spider, with purplish brown coloring and dark legs, sometimes with lighter stripes. The abdomen pattern is described as two clear triangles with lateral bars, but those marks are often dim or missing in the darkest specimens, and the lighter crescent on the front of the abdomen is often absent too. The University of California, Riverside account adds that S. grossa is chocolate brown or dark plum, slightly smaller than a mature black widow, and may have a small white or tan band on the front of the abdomen, while immature specimens often show abdominal dots and a mature female may be uniformly dark. In habitat, S. grossa is a low spider, preferring hidden areas near the ground, under furniture, or in dark low corners, where it hunts woodlice and crawling insects, per the museum guide.
The noble false widow, Steatoda nobilis
Steatoda nobilis is the largest of the three most common false widows in the United Kingdom and the species that has attracted the most public attention. The museum guide gives its size as 8.5 to 14 mm for females and 7 to 10 mm for males, with uniformly red to brown legs. Its abdomen pattern is often called skull shaped, but the guide says it is more like a pentagon, clearer in males and dimmer or absent in females. The University of California, Riverside account describes a thick white or tan band on the front of the abdomen and, on the back in many specimens, a white pattern like a house with a domed or peaked roof pointing forward, often with two dark windows. In some mature specimens only the roof portion remains. The same pale shape is thus described as a skull, a pentagon, and a house, from different angles and at different stages of fading.
Its history is well documented because it is an introduced species. The museum states that it was first recorded in the United Kingdom in the 1870s, likely as a stowaway on cargo ships from its native Madeira and Canary Islands, and only gained a strong foothold from the 1980s onward, in the southern counties first and then spreading northward. The Riverside account records its first documentation in the Western Hemisphere in 2011, in Ventura County, California, with later collections in Monterey, San Diego, Alameda, and Ventura counties, and notes it can be very common where found. Treat that county list as a dated record, not a complete current map, since an expanding species is a moving target. In habitat, S. nobilis prefers elevated positions such as top corners of rooms and conservatories, where it hunts flying insects, with webs usually at least 1.5 meters off the ground, per the museum. That height, size, and pale pattern make it the false widow most likely to be noticed and reported.
The rabbit hutch spider, Steatoda bipunctata
Steatoda bipunctata is the smallest of the three most common false widows in the United Kingdom and the one most tied to outdoor structures. The museum guide gives its size as 4.5 to 7 mm for females and 4 to 5 mm for males. Its most useful mark is a light band down the center of the abdomen, clearer in males but fainter, partial, or missing in females, and its leg stripes are more visible than in the other species. It is widespread and common in Britain and northern Europe, living mainly in and around sheds, pet houses, and garden clutter, sometimes on tree trunks, and also in domestic rubbish dumped outdoors. The name comes from that association with rabbit hutches and similar small outdoor structures. A small, dark, cobweb spider in a shed, with a pale central band and striped legs, fits S. bipunctata better than the larger, plainer cupboard spider or the house-patterned noble false widow, though size and pattern alone cannot confirm it. It is also a reminder that not every false widow lives indoors.
The Mediterranean false widow, Steatoda paykulliana, and the remaining species
Steatoda paykulliana shows why distribution claims need dates and places. The museum guide gives its size as 8 to 13 mm for females and 4.5 to 6 mm for males, with a black body and legs and a midline pattern of triangles or chevrons that can be white, pale yellow, orange, or red. That orange or red coloring is a trap: a reddish mark on top of the abdomen is not the red hourglass underneath that characterizes a true black widow, and the two must never be confused. The guide states that S. paykulliana is not established in Britain but is repeatedly imported with Mediterranean produce, especially grapes, and hides in cracks in the ground and under stones. Its native range covers the Mediterranean countries, southern Europe, and western Asia. A reader who finds a matching spider should therefore consider an imported specimen or a misidentification before assuming an established local population. The museum guide also lists Steatoda albomaculata and Steatoda triangulosa, plus the close relative Asagena phalerata, making six United Kingdom false widows in total. This article gives no detailed profiles for those three, because the museum’s detailed accounts cover the four species above, and inventing comparable detail from weaker sources would mislead readers. The group is larger than its three famous members, and a spider matching none of the main profiles may still be a less common false widow.
Males and females: why one species can look like two
Sexual dimorphism, the visible difference between the sexes, is strong in Steatoda and explains much of the confusion. Females have globular, shiny abdomens and stay with their webs, while males are smaller, with smaller and more clearly marked abdomens, and once mature they leave their webs to search for females. They are therefore the spiders most often seen wandering indoors, especially in summer and autumn. The museum guide states that adult males live only a few months, are usually seen in summer and autumn, cease to feed once mature, and exist at that stage to mate. A small, brightly patterned spider walking across a floor in autumn and a large, plain dark spider in a cupboard web may thus be the male and female of the same species. Males also carry features that help specialists confirm an adult male: swollen pedipalp tips, the short appendages beside the mouthparts modified for transferring sperm, and a stridulatory apparatus of file and scraper type, used in courtship, per the museum guide.
Webs, hunting, and prey
False widows are tangle web spiders. Their webs are a loose tangle of crisscross threads, denser in the center if left undisturbed, per the museum guide. The spider typically hangs upside down in the web, waiting for vibrations that signal prey, with a retreat, a sheltered hiding place, at one edge or in a nearby crevice. The web is not a neat orb or a sheet, but an irregular three dimensional tangle, often with sticky lines running down to the surface below. That design shapes the diet: the cupboard spider hunts woodlice and crawling insects from its low position, while the noble false widow hunts flying insects from its elevated position. False widows eat a wide range of small arthropods, including flies, beetles, woodlice, and other spiders. A web in an undisturbed corner can persist and be reused, so a female with a good corner has little reason to leave it.
Where false widows live around the home
The habitat of the group can be summed up as dark, sheltered, and undisturbed. Indoors, that means cupboards, under furniture, behind appliances, wall cavities, garages, cellars, and rarely opened room corners. Outdoors, it means sheds, outbuildings, garden clutter, log piles, rock crevices, wall cavities, window ledges, and sheltered spots under bark or stored materials. Cupboard spiders favor low positions, noble false widows favor high positions, and rabbit hutch spiders favor sheds and garden structures. A false widow needs a corner left alone long enough for a web to be built and prey to arrive, not a dirty house or neglected garden. Season affects sightings even when spiders are present year round. The museum’s popular article notes that false widows can be seen inside year round, and that autumn reports may partly reflect spiders long unnoticed in dark corners, plus mature males wandering in search of females. The museum guide also calls false widows synanthropic, meaning living almost exclusively in association with people and their buildings. They spread where people and goods travel, in cargo, produce, building materials, and household goods, which is why a species native to Madeira and the Canary Islands can establish in southern England and coastal California, and why a European species can become a common West Coast spider.
Distribution and spread: a story that differs by species
A single map for “the false black widow” would mislead, because each species has a different history. Steatoda grossa is the most cosmopolitan: native to Europe and the Mediterranean region, carried by trade to temperate and subtropical regions worldwide, a common West Coast spider per the Riverside account, and recorded by the museum guide as having colonized England, Wales, and Ireland and as widespread in northern Europe. For a United States reader, S. grossa is an established, widespread species, not a new arrival. Steatoda nobilis has the most dramatic recent history: native to Madeira and the Canary Islands, first recorded in the United Kingdom in the 1870s, gaining a strong foothold only from the 1980s onward, and first documented in the Western Hemisphere in Ventura County, California, in 2011. Later literature describes further establishment elsewhere, but this article does not extend the California county list beyond the Riverside account, since an expanding range needs dated records. Steatoda bipunctata is widespread and common in Britain and northern Europe with no dramatic introduction story, a long established resident rather than a recent traveler. Steatoda paykulliana is the opposite case: a Mediterranean, southern European, and western Asian species reaching Britain mainly as an occasional import in produce, not as an established population. Where sources differ on distribution, the difference usually comes down to date, to a single record versus an established population, or to a native range versus an introduced range.
Life cycle and reproduction
Adult females can live for a few years and survive long periods without water, per the museum guide, while adult males live only a few months, cease to feed once mature, and are usually seen in summer and autumn. A web with a large female may therefore be occupied by the same individual for a long time, while wandering males nearby are short lived visitors at the end of their lives. After courtship, the female lays eggs in white, spherical egg sacs produced at intervals, with the number depending on food supply, from spring through to autumn, per the guide. The eggs hatch in 2 to 4 months. Spiderlings disperse locally by ballooning, floating on silk threads, and over longer distances by transportation of goods by road, rail, and shipping. That combination explains both the steady local presence around buildings and sudden appearances in new regions after a cargo movement. Females guard their egg sacs in or near the web. Young spiders often show clearer patterns than adults, which is another reason a photograph of a young spider can be hard to identify.
Why false widows are so often misidentified
Five reasons work together. First, the resemblance to true black widows is real: the groups share a family, a body plan, a web type, and a dark color range, so a quick glance genuinely cannot separate them. Second, the group name covers several species, so no single description fits every false widow. Third, markings fade with age and vary between individuals, so the features guides emphasize are the features most likely to be missing in the spider actually found. Fourth, males, females, and young spiders look different, so one species can present as several different looking animals across a season. Fifth, media coverage has given the noble false widow a reputation that spills over onto the whole group. The museum’s popular article notes that reports of more severe encounters are usually not backed up with formal spider identification, and that false widows have unjustly earned a reputation as a dangerous pest. Readers should therefore treat dramatic individual stories with caution, especially when the spider was never formally identified, and give more weight to museum and university accounts of the group as a whole. Body length excludes the legs, so a spider described online as 15 mm or larger may be a leg span figure, not a body length.
Living alongside false widows: general information
This article is a species explainer, not a pest control guide, and it gives general information only. It does not give bite diagnosis, treatment advice, or medical guidance, and it does not present a control program. False widows are shy spiders. The museum guide states that they are not aggressive and do not attack people, and that encounters happen when a spider is accidentally trapped between skin and clothing, for example in gloves or boots left unused for a while. A false widow in a web in an undisturbed corner is not seeking contact; it is waiting for prey in the one place it has chosen, and it will normally retreat to its hiding place when disturbed. For a spider that cannot be identified, the safest general approach is distance and expert help, not handling. Photographing the spider from a safe distance, noting where it was found, how high it was, and what its web looked like, gives an identification service far more to work with than a description from memory. Ecologically, false widows eat flies, woodlice, beetles, and other small invertebrates from a fixed web.
Frequently asked questions
Is a false black widow the same as a black widow?
No. A false black widow is in the genus Steatoda. A true black widow is in the genus Latrodectus. Both genera are in the family Theridiidae, which explains their similar appearance and webs, but they are different groups of species.
Which species is the false black widow?
There is no single answer. In the United States it most often means Steatoda grossa, the cupboard spider. In Britain, “false widow” on its own often means Steatoda nobilis, the noble false widow, in popular use. Others include Steatoda bipunctata and Steatoda paykulliana. Always ask which species a source means.
How can I tell a false black widow from a true black widow?
Look first for the bright red hourglass on the underside, typical of an adult female true black widow and absent in a false black widow. Then consider size, upper pattern, leg color, web type, and habitat. No single feature is decisive, since markings fade and males and young spiders differ from adult females.
Why does my false widow look plain dark when the guide shows a patterned spider?
Pattern fades with age and varies between individuals, especially in females. The museum guide notes markings are clearer in males and dimmer or absent in females, and that the darkest Steatoda grossa often lose their triangle and bar pattern entirely. Age, sex, and species all affect pattern.
Are male and female false widows different species?
No. Females are larger, with globular, shiny abdomens, and stay with their webs. Males are smaller, with smaller and more clearly marked abdomens, and once mature they leave their webs to search for females. A small patterned wandering spider and a large plain web spider nearby may be the same species.
Where are false widows most likely to be found?
In dark, sheltered, undisturbed places: cupboards, under furniture, garages, and cellars indoors; sheds, garden clutter, and log piles outdoors. Cupboard spiders favor low positions, noble false widows favor high positions, and rabbit hutch spiders favor sheds. They are noticed most in summer and autumn, when mature males wander.
Is the noble false widow spreading?
Yes, in the sense documented by museum and university sources. Steatoda nobilis, native to Madeira and the Canary Islands, was first recorded in the United Kingdom in the 1870s, expanded strongly from the 1980s onward, and was first documented in the Western Hemisphere in Ventura County, California, in 2011. Its range is still changing, so lists and maps should be read with their dates attached.
What should I do if I find a spider I cannot identify?
Keep your distance, do not handle it, and seek expert identification from a local university extension service or museum identification service. Note where it was found and what its web looked like, and photograph it from a safe distance if possible.
Keep reading: Black Spider With White Spots
Sources & references
- Natural History Museum, London. Identifying false widow spiders. https://www.nhm.ac.uk/take-part/identify-nature/spiders-in-your-home/false-widow-spiders.html
- Natural History Museum, London. How dangerous are false widow spiders? https://www.nhm.ac.uk/discover/how-dangerous-are-false-widow-spiders.html
- Natural History Museum, London, Identification and Advisory Service. False Widow Spiders (identification guide). http://www.nhm.ac.uk/resources-rx/files/false-widow-identification-129901.pdf
- University of California, Riverside, Center for Invasive Species Research. European Spider, Steatoda nobilis. https://cisr.ucr.edu/invasive-species/european-spider
- University of California Statewide IPM Program. Black Widow Spider. https://ipm.ucanr.edu/agriculture/grape/black-widow-spider/
- Colorado State University Extension. Western Widow Spider. https://extension.colostate.edu/resource/western-widow-spider/
