False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded, bulbous abdomen, comb-like setae on the fourth tarsus for pulling silk, and generally poor eyesight.
Physical Description
The spider has a compact, glossy appearance with a distinctively domed, bulbous abdomen. The cephalothorax is rounded and smooth. The specimen visible appears to be an adult male, identifiable by the enlarged, bulbous palps at the front used for mating.
Size Estimate
Body length typically ranges from 6 to 10.5 mm for females, while males are slightly smaller at 4 to 6 mm. The leg span can reach up to 20 to 30 mm.
Coloration & Markings
Coloration ranges from deep brownish-purple to glossy black or dark charcoal. Some specimens display subtle lighter pale or yellowish markings, chevrons, or crescents on the upper surface of the abdomen, though mature males often appear darker and more uniformly glossy.
Web Type
Builds a messy, irregular, three-dimensional tangle web commonly known as a cobweb. This web is typically constructed in dark, protected corners near ground level, inside hollows, or within human structures like garages and basements.
Eye Arrangement
Consists of eight small eyes arranged in two parallel, slightly curved rows of four. The eyes are generally uniform in size and lack the prominent relative scaling found in families like Lycosidae or Salticidae.
Leg Characteristics
Legs are relatively long, thin, smooth, and taper toward the ends, lacking prominent spines but featuring fine hairs. They are usually a lighter reddish-brown or yellowish-brown, sometimes showing faint darker banding.
Venom & Safety Information
Venom Information
Possesses a neurotoxic venom containing latrotoxin-like compounds, though significantly less potent than that of true widow spiders (Latrodectus).
Medical Significance
Minimally dangerous to humans. Bites are rare and usually only occur when the spider is pressed directly against the skin. Symptoms are generally mild, comparable to a wasp sting, featuring localized pain, redness, and occasional blistering. Systemic effects are very uncommon.
Safety Recommendations
Avoid handling spiders with bare hands. If found inside a home, gently capture the spider using a cup and a piece of paper, then release it outdoors. No professional pest control is typically necessary.
Habitat & Behavior
Habitat & Range
Found globally in temperate regions, particularly common throughout Europe, North America, Australia, and New Zealand. Prefers dark, humid microhabitats, frequently found indoors in basements, crawlspaces, and sheds, or outdoors beneath rocks, logs, and bark.
Behavior & Temperament
Non-aggressive and reclusive. They spend the vast majority of their time stationary within their cobwebs, waiting for prey. When disturbed, they typically drop to the ground, curl into a ball, or retreat hastily rather than biting.
Diet & Prey
Feeds primarily on crawling and flying insects, woodlice, and occasionally other spiders. Prey stumbling into the sticky lower threads of the cobweb is quickly wrapped in silk and subdued with venom.
Seasonal Activity
Active year-round indoors, but most commonly noticed in late summer and autumn when mature males wander extensively in search of mates.
Description
The False Black Widow (Steatoda grossa) is a frequent co-inhabitant of human structures, often mistaken for its dangerous relative, the Black Widow, due to its dark, bulbous physique. Despite its intimidating appearance, it is a timid and beneficial pest controller that quietly manages populations of household insects.
Key Features
Glossy, bulbous, dark brown to black abdomen, lack of the characteristic red hourglass marking found on true widows, and presence of elongated, slender legs relative to the compact body.
Similar Species
True Black Widow (Latrodectus spp.), which features a distinct red hourglass or bright spots and lacks the matte or purplish-brown tones often seen in Steatoda grossa. Other Steatoda species like Steatoda triangulosa are distinguished by distinct geometric patterns.
Life Cycle
Females construct tough, silken egg sacs containing up to several hundred eggs, guarding them nearby. Spiderlings hatch after a few weeks, disperse via ballooning or crawling, and undergo multiple molts over a lifespan of several years.
Ecological Importance
Acts as an effective natural predator for common household and garden pests, helping to control populations of flies, beetles, cockroaches, and woodlice.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and thriving globally as a synanthropic species.
Interesting Facts
Despite the alarming common name, Steatoda grossa is actually known to prey on true black widows when they encounter them, occasionally successfully subduing much more dangerous spiders.
Photography Tips
Use macro lenses with good lighting to highlight the glossy texture of the cephalothorax and abdomen. Photograph from a top-down or side angle to accurately capture leg proportions and any faint dorsal markings.
Identified: 2026-08-29T17:36:53.929692