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, sticky tangle webs.
Physical Description
The spider has a distinct pear-shaped or globular abdomen that is plump and smooth, joined to a smaller, oval cephalothorax. The body appears robust, glossy, and smooth with minimal visible hair compared to wolf spiders or tarantulas.
Size Estimate
Body length ranges from 6 to 10.5 mm for females, while males are slightly smaller at 4 to 6 mm. Leg span reaches approximately 20 to 30 mm. This specimen appears to be an adult or subadult female.
Coloration & Markings
Deep brownish-purple to nearly black base coloration, often featuring faint, pale yellowish or white chevron-like or crescent markings across the dorsal side of the abdomen. The legs are a lighter brownish tone with subtle darker banding.
Web Type
Builds an irregular, sticky tangle web often referred to as a cobweb. These webs are constructed in dark, sheltered areas close to the ground or in structural corners, featuring strong, sticky vertical threads designed to snare crawling insects.
Eye Arrangement
Consists of eight small eyes arranged in two parallel, slightly curved rows of four across the front of the cephalothorax, typical of the theridiid family.
Leg Characteristics
Legs are moderately long, slender, and taper toward the ends. They feature subtle dark bands or rings against a lighter brown background and lack heavy spines or specialized large claws, but possess comb-like structures on the hind tarsi.
Venom & Safety Information
Venom Information
Contains latrotoxin-like components in its venom, though significantly less potent than true black widows. Venom is neurotoxic in nature but generally causes only localized pain, redness, and mild swelling in humans.
Medical Significance
Low medical significance. Bites are rare and usually occur only when the spider is pressed directly against the skin. Symptoms are mild and self-limiting, occasionally accompanied by slight malaise, resolving within a day without specific treatment.
Safety Recommendations
Practice caution when reaching into dark, undisturbed storage areas or moving woodpiles. If found indoors, the spider can be safely relocated outside using a cup and a piece of paper.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution found worldwide in temperate regions. Prefers dark, humid microhabitats such as basements, crawlspaces, under furniture, inside hollow logs, beneath rocks, and around the exterior foundations of buildings.
Behavior & Temperament
Docile and non-aggressive. They spend most of their time stationary within their retreat or web. When disturbed, they typically drop from the web and play dead or scurry rapidly toward a hiding spot rather than bite.
Diet & Prey
Primarily feeds on crawling and flying insects such as beetles, flies, ants, roaches, and occasionally other spiders. Prey is wrapped rapidly with sticky silk before being bitten and consumed.
Seasonal Activity
Active year-round indoors, though peak activity and wandering males seeking mates are most commonly observed during late summer and autumn.
Description
The False Black Widow (Steatoda grossa) is a common yet frequently misunderstood synanthropic spider often mistaken for its dangerous relative, the black widow. With its glossy, bulbous dark body and subtle pale markings, it quietly goes about its life in the corners of basements and outbuildings. As an efficient predator of household pests, it serves a valuable ecological role despite its slightly intimidating appearance.
Key Features
Glossy, globular dark brown to purplish abdomen; absence of a red hourglass marking; presence of faint pale chevron markings on the upper abdomen; slender, unspined banded legs; and an irregular tangle web.
Similar Species
True Black Widow (Latrodectus spp.), which features a shiny black body with a distinct red hourglass or red spots on the underside of the abdomen. Other Steatoda species like Steatoda triangulosa (Triangle Spider) have distinct patterned markings instead of plain chevrons.
Life Cycle
Females produce papery, brownish silk egg sacs containing up to several hundred eggs, which are guarded within the web. Spiderlings hatch after a few weeks, disperse via ballooning or crawling, and undergo multiple molts to reach maturity. Lifespan can exceed several years for females.
Ecological Importance
Functions as a natural pest control agent in domestic and wild ecosystems, keeping populations of common household insects and other arthropods in check.
Conservation Status
Not evaluated by the IUCN, but populations are secure, highly stable, and often expanding due to human urban development and widespread global distribution.
Interesting Facts
Despite their common name implying danger, false black widows actively compete with true black widows and can occasionally prey upon them. They are exceptionally long-lived for spiders, with adult females surviving for up to six years.
Photography Tips
Use a macro lens with good side lighting to highlight the glossy texture and subtle pale patterns of the abdomen. Photograph from a slight distance to avoid startling the spider into dropping from its web.
Identified: 2026-09-04T03:23:21.947464