False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a generally globose abdomen, comb-like setae on the fourth tarsus used for pulling silk over prey, and irregular tangle webs.
Physical Description
The spider has a glossy, bulbous, egg-shaped abdomen and a relatively compact, smooth cephalothorax. The body appears plump and stout, typical of theridiid spiders, and shows clear sexual dimorphism where females are noticeably larger and rounder than males.
Size Estimate
Body length ranges from roughly 6 to 10.5 mm for females, with a leg span reaching up to 20 to 25 mm. This specimen appears to be an adult female based on the robust, rounded abdominal proportions.
Coloration & Markings
The coloration is typically dark brownish-purple to nearly black, often with subtle lighter cream or yellowish markings, sometimes including faint chevron patterns or pale bands on the dorsal abdomen, though these can be dark and obscure.
Web Type
Builds an irregular, sticky tangle web often referred to as a cobweb, typically constructed in dark, undisturbed, low-to-the-ground locations such as corners, crevices, and beneath furniture or outdoor structures.
Eye Arrangement
Features eight small eyes arranged in two rows of four, typical of the Theridiidae family, consisting of two parallel rows where the lateral eyes are often touching.
Leg Characteristics
The legs are moderately long, slender, and smooth without prominent spines, displaying a brownish tone that matches the cephalothorax. They typically curl inward tightly when the spider is startled or deceased.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom (specifically latrotoxin-like components, though less potent than true widow spiders), which is used primarily to subdue invertebrate prey.
Medical Significance
Not considered medically significant to humans. While a bite can cause localized pain, redness, and mild systemic symptoms like malaise in rare cases, it is not dangerous or life-threatening.
Safety Recommendations
Seal entry points to homes, wear gloves when cleaning dark, undisturbed storage areas, and safely relocate spiders outside using a cup and card if found indoors.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, widely found in temperate and subtropical regions worldwide, commonly inhabiting human dwellings, outbuildings, garages, bark, and rock crevices.
Behavior & Temperament
Docile and non-aggressive; these spiders prefer to retreat or play dead rather than bite when disturbed. They are nocturnal web-dwellers that spend most of their time hanging upside down in their webs.
Diet & Prey
Feeds primarily on crawling and flying insects trapped in its sticky web, including roaches, woodlice, flies, and occasionally other spiders.
Seasonal Activity
Active year-round indoors, with peak outdoor visibility during the warmer spring and summer months when mating occurs.
Description
Steatoda grossa, commonly known as the false black widow, is a frequent indoor and outdoor neighbor. Often mistaken for its more dangerous relative due to its dark, glossy appearance and bulbous abdomen, this harmless cobweb spider plays an effective role in controlling household insect populations.
Key Features
Glossy bulbous abdomen, dark brownish to purplish coloration, lack of a red hourglass marking, and construction of an irregular 3D cobweb in dark corners.
Similar Species
True Black Widow (Latrodectus species), which can be distinguished by the prominent red hourglass marking on the underside of the abdomen and jet-black matte coloration.
Life Cycle
Females produce spherical silk egg sacs containing dozens to hundreds of eggs. Spiderlings disperse via ballooning or crawling after hatching, maturing over several months through multiple molts.
Ecological Importance
Acts as an effective natural pest controller in homes and gardens, keeping populations of crawling and flying insects in check.
Conservation Status
Not evaluated by the IUCN, but populations are secure, highly stable, and often expanding due to human habitation.
Interesting Facts
False black widows are known to occasionally prey on true black widows by invading their webs and wrapping them up using superior silk-casting techniques.
Photography Tips
Photograph from a macro perspective using natural side-lighting or an external diffuser to highlight the glossy texture of the abdomen without creating harsh reflections.
Identified: 2026-09-13T12:04:38.187896