Steatoda borealis
Steatoda borealis is the northern false widow of eastern North America — a small, glossy brown cobweb spider with a pale T-shaped mark on the front of its abdomen. It lives under bark and stones outdoors and in the cool, forgotten corners of basements and sheds, and although it looks enough like a widow to worry people, its bite is a minor event.
By Dr Richard J. Pearce (PhD)Published May 13, 2022Updated September 13, 2026✓ Reviewed by Dr. James Watuwa
In this guide
Physical description and identification
Steatoda borealis is a small, hard-looking cobweb spider with a strongly domed abdomen and short, sturdy legs — the classic build of the genus Steatoda, the group known as the false widows. It is the species most North Americans have in mind when they report a "small black widow" in a basement, and in most of those cases the identification is wrong in a reassuring direction.
Adults
- Size: females run roughly 5–7 mm in body length and males about 4–5 mm, so the sexes are close in size rather than wildly different as in true widows. Around 0.7 cm is a fair figure for a mature female; the domed abdomen makes it look heavier than the measurement suggests.
- Colour: the abdomen is glossy and ranges from reddish brown through chocolate to a deep purplish black, and it reflects light like varnish. Across the front of the abdomen sits a narrow pale cream or yellowish band, and a pale median stripe runs back from the middle of that band. Together they form the T- or Y-shaped figure that is the best single field mark for the species. The carapace is dark reddish brown and the legs are orange-brown, often darker at the joints.
- Eyes: eight small eyes in two rows of four, closely grouped and all of similar size — no enlarged pair, which rules out jumping and wolf spiders at once. Our guide to spider eyes covers the patterns that separate the families.
- Legs: the first and fourth pairs are clearly longer than the second and third, giving the spider a slightly crab-like stance in the web. The legs are short and thick compared with the long, wiry legs of a true widow, and there is no red hourglass anywhere on the body.
- Comb foot: a row of curved, toothed bristles on the tarsus of the fourth leg lets the spider fling gluey silk over prey from a safe distance — the trait that names the comb-footed spider family.
Eggs and egg sac
The female builds a rounded white silk sac and hangs it deep in her tangle, close to the crevice she shelters in. She stays with it rather than abandoning it, and will often be found sitting alongside the sac when a stone or a piece of loose bark is lifted. Several sacs may be produced through a single warm season by a well-fed female.
Spiderlings
The young are pale with a distinctly reddish or orange cast when they first leave the sac, and they already show the swollen abdomen of the family. They stay near the mother's web for a short while, then disperse to spin their own small tangles under nearby bark, stones and ledges. Colour deepens with each moult until the adult pattern appears; the whole sequence from egg to adult is set out in our guide to the spider life cycle.
The web
The web is an irregular, three-dimensional snarl of silk with no recognisable geometry: a dense mesh where the spider shelters, tangled support threads above and behind it, and taut vertical lines running down to the surface beneath. Those lower lines are the working part. Their tips carry glue and are only lightly fixed to the ground, so an insect that touches one pulls the anchor loose and is hoisted off its feet. The spider then hauls it up, throws silk over it and bites. Webs are spun in the dry, protected spaces this species prefers: under loose bark, beneath stones and boards, in rock crevices, in the angle of a foundation wall, behind basement shelving. See how spider webs work for how this compares with the orb of a garden spider.
Where Steatoda borealis lives
Steatoda borealis is a North American species with a distinctly northern distribution, as the name suggests. It is widespread across southern Canada and through the northern and eastern United States, from the Atlantic provinces and Ontario south through New England and the Appalachians and west across the Great Lakes states. It thrives in climates too cold for most of the false widows that have spread around the world, and it handles a hard winter without difficulty.
Outdoors it is a spider of crevices: under slabs of loose bark on standing and fallen trees, beneath stones and logs, in the gaps of rock outcrops and stone walls, under bridges and in the cracks of retaining walls. Around buildings it moves into the cool, low-traffic parts — basements, crawl spaces, attics, garages, sheds, window wells, under porches and decks. It avoids heated, frequently disturbed rooms, which is where you are more likely to meet the common house spider or a Parasteatoda instead.
The practical consequence is that most sightings come from people moving something that has not been moved for a while: a woodpile, a flagstone, a stack of boxes in the cellar. Its relatives across the Atlantic occupy very similar niches, and the rabbit hutch spider fills almost exactly the same role in European outbuildings.
Are Steatoda borealis spiders venomous?
Yes in the trivial sense that it uses venom on its prey, and no in the sense that matters: it is not medically significant. Steatoda venom lacks the α-latrotoxin load that makes true widow venom capable of causing latrodectism, the cramping syndrome that sends people to hospital after a northern black widow bite. The false widows are called false precisely because the resemblance is skin deep — same family, same rounded body, entirely different clinical picture.
Even within its own genus this is a mild species. The Steatoda most often associated with painful bites is Steatoda nobilis, the noble false widow, a larger, warmth-loving spider that has spread across western Europe and parts of California and Chile. S. borealis is smaller, has shorter fangs and lives in places where people rarely press bare skin against it.
Can Steatoda borealis spiders bite?
It can, but it almost never does. This is a slow, sedentary spider whose instinct when disturbed is to freeze or drop out of the web on a dragline rather than to defend itself. Recorded bites involve the spider being handled or squeezed against skin — inside a glove, a sleeve, or between a hand and the underside of a board being lifted.
The effect is minor. Most people describe a sharp pinch at the moment of the bite, followed by local pain, a small red mark and occasionally a little swelling or itching, all of which settle within a day or so. There is no tissue destruction, no spreading muscle cramp and no systemic illness. Wash the area with soap and water, apply a cold pack if it is uncomfortable, and keep it clean. Seek medical advice only if the site shows signs of infection over the following days, or if the person has an allergic reaction — neither of which is a venom effect.
False widow or black widow? Look for red and look at the legs. Steatoda borealis is brown, with a pale T-shaped mark at the front of the abdomen, short thick orange-brown legs and no red anywhere. A true widow is glossy black with a red hourglass or red spots underneath and long, thin, shiny legs. If you are in a northern basement, the odds overwhelmingly favour the false widow.
Ecological importance and behavior of Steatoda borealis
This is a patient, nocturnal, web-bound hunter. It spends daylight tucked into its retreat and takes up position at the edge of the tangle after dark, judging everything that happens by the vibration reaching its legs through the silk. It does not roam, and an individual may occupy the same crevice for its entire adult life, simply extending the web as it grows.
Diet: prey is whatever walks beneath the gumfoot lines — crickets, cockroaches, ground beetles, ladybird beetles, ants, earwigs, woodlice, silverfish and other spiders. In a basement or crawl space that makes it a genuinely useful resident, quietly removing the crawling insects that would otherwise accumulate there.
Spider-eating and competition: Steatoda species are well known for preying on other spiders, including true widows, and this is often cited for S. borealis because its range overlaps the northern black widow in parts of the eastern United States. The claim should be stated carefully: predation on Latrodectus is best documented for Steatoda grossa, and for S. borealis the stronger evidence is for competition over the same crevice habitat rather than routine widow-hunting. Either way, a false widow in the woodpile is not a bad neighbour to have.
Natural predators: larger spiders, including cellar spiders and other theridiids, take them readily. Mud-dauber wasps sting them and pack them into mud cells for their larvae, centipedes hunt them in the same crevices, and insectivorous birds take exposed individuals. Egg sacs are vulnerable to ants and parasitoid wasps.
Seasonal behaviour: because it shelters in bark crevices, rock cracks and buildings, this species survives northern winters as a juvenile or adult and can be found in almost any month — one reason it appears in midwinter basement reports when most spiders have vanished. Mating and egg-laying concentrate in the warmer half of the year, and males become more mobile then as they search for females.
Relationship with humans: harmless and beneficial. If a web is unwanted, sweep it away and seal the gap it was built in; no chemical treatment is warranted for a spider this innocuous.
Similar spiders and how to tell them apart
| Spider | How it differs from Steatoda borealis |
|---|---|
| Northern black widow (Latrodectus variolus) | Glossy jet black with a row of red spots on top and a split red hourglass beneath, plus long thin wiry legs. Medically significant; S. borealis is not. |
| False black widow (Steatoda grossa) | Larger and darker purplish brown, with faint pale crescents rather than a crisp T at the front of the abdomen. More strongly tied to heated buildings. |
| Rabbit hutch spider (Steatoda bipunctata) | Very similar in size and build. It shows a simple pale band across the front of the abdomen with a broken midline stripe, rather than the clean T or Y of S. borealis. |
| Noble false widow (Steatoda nobilis) | Bigger, with cream markings often likened to a skull and brighter reddish legs. Absent from most of the northern range of S. borealis. |
| Triangulate cobweb spider (Steatoda triangulosa) | Paler, with a cream abdomen carrying a zigzag row of dark triangles and much more slender legs. Very common in the same basements. |
| Parasteatoda | The common house cobweb genus. Rounder, softer looking, mottled tan to grey rather than glossy dark brown, and usually higher up in a room corner. |
Quick facts
| Distribution | North America: southern Canada and the northern and eastern United States. |
|---|---|
| Habitat | Under loose bark, stones and boards, in rock crevices and stone walls, and in basements, attics, crawl spaces, garages and sheds. |
| Diet | Crickets, cockroaches, ground and ladybird beetles, ants, earwigs, woodlice, silverfish and other spiders. |
| Lifespan | Typically one to two years; individuals overwinter and can be found year-round. |
| Predators | Larger spiders, cellar spiders, mud-dauber and parasitoid wasps, centipedes and insectivorous birds. |
| Web | Irregular tangle in a crevice with sticky gumfoot lines dropping to the surface below. |
| Venom | Not medically significant; bites cause brief local pain and redness at most. |
| IUCN status | Not evaluated. Common across its range. |
Did you know?
- Nicholas Marcellus Hentz, who described this spider in 1850, was born in Versailles and emigrated to the United States as a boy. He worked as a teacher and taught himself arachnology, and he is regarded as the founder of the subject in North America.
- Little of Hentz's original spider material survives, so his published illustrations have carried much of the weight of defining the species he named — one reason nineteenth-century American spider names took so long to settle.
- The genus name Steatoda comes from the Greek for tallow or suet, a reference to the fat, glossy abdomen rather than to anything menacing. The epithet borealis simply means northern.
- Gumfoot webs are one of the great engineering tricks of the spider world: by gluing the threads only at the bottom, a small spider can lift prey much heavier than itself clean off the ground before it has a chance to fight back.
- Because it shelters in crevices and tolerates cold, this is one of the spiders you can still find active in an unheated cellar in midwinter — see where spiders go in winter for how they manage it.
In summary, Steatoda borealis is a small, glossy, cold-hardy false widow that hunts crawling insects from a tangle web under bark, stones and basement shelving across the northern half of North America. Learn the pale T at the front of the abdomen and the short orange-brown legs, and the widow scare goes away for good.
Frequently asked questions about the steatoda borealis
What does a Steatoda borealis spider look like?
It is a small, glossy spider about 5 to 7 millimetres long with a strongly domed reddish-brown to purplish-black abdomen. A pale cream band crosses the front of the abdomen with a stripe running back from it, forming a T or Y shape. The legs are short, thick and orange-brown.
Is the Steatoda borealis spider venomous to humans?
It has venom for subduing insects, but it is not medically significant to people. Its venom does not contain the alpha-latrotoxin load that causes latrodectism in true widow bites. A bite may sting briefly and leave a small red mark, and healthy adults need no specific treatment.
Where are Steatoda borealis spiders commonly found?
They live across southern Canada and the northern and eastern United States. Outdoors they occupy crevices under loose bark, stones, logs and in rock walls. Around buildings they settle in basements, crawl spaces, attics, garages, sheds and window wells rather than heated, busy rooms.
What happens if a Steatoda borealis bites you?
Expect a sharp pinch at the moment of the bite, then mild local pain, a small red mark and sometimes slight swelling or itching that fades within a day. There is no tissue damage or systemic illness. Wash the area, use a cold pack if sore, and watch only for signs of infection.
What kind of web does a Steatoda borealis build?
It builds an irregular three-dimensional tangle with no geometric pattern: a dense retreat in a crevice, scaffold threads above it, and taut sticky lines dropping to the surface below. Those lower gumfoot threads snatch crawling insects off their feet when the glued tips pull free.
Why is Steatoda borealis called a false widow spider?
Because it belongs to the same family as true widows and shares their swollen, rounded abdomen and tangle web, so it gets mistaken for one. It has no red hourglass, its legs are short and thick rather than long and wiry, and its venom is far weaker than a widow's.
How can you identify a Steatoda borealis spiderling?
Newly emerged spiderlings are pale with a reddish or orange cast and already have the swollen abdomen typical of the family. They emerge from a rounded white silk sac guarded by the female and darken toward the adult pattern with each moult as they disperse to nearby crevices.
Does Steatoda borealis eat black widow spiders?
Steatoda species are known to prey on other spiders, and the claim that they eat widows is often repeated for this species. The evidence is strongest for Steatoda grossa. For Steatoda borealis, competition with widows for the same crevice habitat is better supported than routine predation.
How is Steatoda borealis different from the northern black widow?
The northern black widow is glossy jet black with a row of red spots on top and a split red hourglass underneath, and it has long thin wiry legs. Steatoda borealis is brown with a pale T mark at the front of the abdomen, short thick legs and no red markings at all.
Are Steatoda borealis spiders active in winter?
Yes. Because they shelter in bark crevices, rock cracks and buildings, they survive cold weather as juveniles or adults and can be found in almost any month. That is why they turn up in midwinter reports from basements and crawl spaces when most other spiders have disappeared.
References
- World Spider Catalog (2026). Steatoda borealis (Hentz, 1850). Natural History Museum Bern. wsc.nmbe.ch/spec-data/46079/taxon
