False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a globular abdomen, comb-like setae on the fourth tarsus used for flinging silk over prey, and typically building irregular, tangled three-dimensional webs.
Physical Description
The spider has a bulbous, glossy, oval-shaped abdomen and a relatively small, smooth cephalothorax. Females are robust with a plump, shiny abdomen, while males are much smaller, narrower, and have longer legs.
Size Estimate
Body length ranges from 6 to 10.5 mm for females and 4 to 6 mm for males, with a leg span up to 25 to 35 mm. This appears to be an adult female specimen based on the large, globular abdomen and glossy appearance.
Coloration & Markings
Deep purplish-brown to glossy black base coloration, often with lighter grayish, yellowish, or reddish-brown markings, including faint chevron patterns or crescent shapes on the upper abdomen. The carapace matches the dark brown tone of the legs.
Web Type
Builds an irregular, tangled three-dimensional cobweb in dark, undisturbed areas such as corners, under furniture, or near ground level. The web features sticky silk threads designed to snare crawling insects.
Eye Arrangement
Eight small, dark eyes arranged in two horizontal rows of four each, typical of the family Theridiidae, with lateral eyes often touching or closely grouped.
Leg Characteristics
Long, slender, dark brown legs lacking prominent spines but featuring fine hairs. The legs are typically splayed outward against a surface in a characteristic cobweb spider posture.
Venom & Safety Information
Venom Information
Neurotoxic venom, though significantly less potent than that of true widow spiders (Latrodectus spp.). It is not typically dangerous to humans, but bites can cause localized pain, redness, and mild systemic symptoms in sensitive individuals.
Medical Significance
Low medical significance. Bites are rare and usually occur only when the spider is trapped against the skin. Symptoms are generally limited to mild localized pain and swelling that resolve within a day, though rare steatodism cases can cause fever or malaise.
Safety Recommendations
Wear gloves when cleaning dark, undisturbed spaces like garages or basements. If found indoors, gently relocate the spider outside using a container and a piece of card. Seek medical attention only if an unusual allergic reaction or severe pain occurs following a bite.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, widely found in temperate regions worldwide including North America, Europe, and parts of Australia. Prefers dark, humid microhabitats around human habitations, basements, sheds, garages, under logs, and beneath rocks.
Behavior & Temperament
Docile and non-aggressive. They spend most of their time hanging upside down in their webs. When disturbed, they typically retreat to a nearby crevice, drop to the ground, or curl up rather than bite.
Diet & Prey
Feeds primarily on crawling and flying insects such as flies, beetles, woodlice, cockroaches, and occasionally other spiders. They wrap prey in sticky silk before delivering a paralyzing bite.
Seasonal Activity
Active year-round indoors, but most commonly encountered during late summer and autumn when mature males wander in search of females during the mating season.
Description
The False Black Widow (Steatoda grossa) is a frequent indoor companion often mistaken for its dangerous relative, the black widow. With its glossy, dark, bulbous body and preference for quiet corners, this cobweb weaver serves as a stealthy predator of household pests. While it can startle homeowners, it is a shy creature that prefers fleeing to fighting.
Key Features
Glossy, globular dark brown to purplish abdomen; absence of a red hourglass marking; irregular cobweb construction; smooth, dark legs without distinct banding.
Similar Species
True Black Widow (Latrodectus spp.), which features a distinct red hourglass or red spots on the underside of the abdomen. Other Steatoda species like Steatoda triangulosa, which has a distinct triangular pattern on the back.
Life Cycle
Females produce spherical, papery silk egg sacs containing up to 200 eggs, often hidden within the web structure. Spiderlings hatch after a few weeks, disperse via ballooning or crawling, and undergo multiple molts over a multi-year lifespan.
Ecological Importance
Acts as an effective natural pest control agent in and around human structures by significantly reducing populations of nuisance insects and other arthropods.
Conservation Status
Not evaluated by the IUCN, but secure and highly abundant globally, often thriving alongside human development.
Interesting Facts
Despite their common name and superficial resemblance to black widows, false black widows are known to occasionally prey on true black widows by invading their webs and subduing them with specialized silk-throwing tactics.
Photography Tips
Use macro lenses with a high depth of field to capture the glossy texture and subtle markings of the abdomen. Photograph from the side or slightly above while avoiding sudden movements that might cause the spider to retreat.
Identified: 2026-09-07T10:27:11.412875