False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a generally globose abdomen, comb-like serrated bristles on the tarsus of the fourth leg used for flinging silk, and building irregular tangle webs.
Physical Description
The spider has a glossy, bulbous, egg-shaped abdomen that overhangs the cephalothorax slightly. The overall body texture is smooth and shiny with minimal prominent hairiness visible to the naked eye. The proportions feature a compact cephalothorax and a larger, rounded abdomen typical of comb-footed spiders.
Size Estimate
Small to medium-sized spider, with a body length estimated around 6 to 10 millimeters and a leg span of roughly 15 to 20 millimeters. This specimen appears to be an adult or sub-adult based on its proportional development.
Coloration & Markings
Deep brownish-purple to blackish base coloration, often featuring faint, lighter yellowish or cream-colored geometric markings, chevrons, or a crescent shape on the anterior dorsal portion of the abdomen. The legs exhibit subtle darker banding.
Web Type
Builds an irregular, three-dimensional tangle web or cobweb, typically constructed in dark, sheltered areas close to the ground or in structural crevices like corners, under furniture, or around doorframes.
Eye Arrangement
Eight small eyes arranged in two slightly curved horizontal rows of four each across the front of the cephalothorax, typical of the Theridiidae family.
Leg Characteristics
Legs are moderately long and slender, tapering away from the body, featuring faint darker annulations (banding). They lack heavy spination but possess the characteristic comb-like setae on the fourth pair of legs used for manipulating silk.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom (specifically latrotoxin-like components, though much milder than true black widows). Bites are rare and usually occur only when the spider is trapped against human skin.
Medical Significance
Not considered dangerously venomous to humans. A bite can cause mild local pain, redness, and swelling similar to a wasp sting, occasionally accompanied by mild malaise, but serious systemic symptoms are extremely rare.
Safety Recommendations
Avoid direct handling with bare hands. When cleaning dark corners, wear gloves. If relocation is necessary, gently guide the spider into a container using a piece of card and release it outdoors.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, frequently found worldwide in temperate and warm regions. Prefers dark, humid human habitations, outbuildings, basements, garages, under logs, and in rock crevices outdoors.
Behavior & Temperament
Generally nocturnal, shy, and non-aggressive. They spend most of their time hanging upside down in their webs, retreating rapidly when disturbed or dropping to the ground and feigning death.
Diet & Prey
Feeds on a wide variety of crawling and flying insects, including woodlice, flies, mosquitoes, beetles, and occasionally other spiders, subduing them with sticky silk before delivering venom.
Seasonal Activity
Active year-round indoors, but most commonly noticed during late summer and autumn when mature males wander in search of females during the mating season.
Description
The False Black Widow is a frequent indoor companion that often goes unnoticed in the corners of garages, basements, and undisturbed cupboards. With its glossy, bulbous abdomen and dark coloration, it closely resembles its more infamous relative, the black widow, but lacks the dangerous potency. As a skilled cobweb architect, it quietly patrols homes for wandering insect pests, making it a beneficial, albeit sometimes misunderstood, resident.
Key Features
Glossy, globose abdomen; dark brown to purplish coloration; lack of a red hourglass marking; presence of subtle pale geometric markings on the upper abdomen; irregular cobweb construction.
Similar Species
Latrodectus species (True Black Widows), which feature the distinctive red hourglass marking on the underside of the abdomen. Steatoda triangulosa (Triangle Weaver), which features a distinct zigzag pattern on the back.
Life Cycle
Females construct tough, paper-like silk egg sacs containing dozens to hundreds of eggs. Spiderlings hatch after a few weeks, disperse via ballooning or crawling, and molt multiple times over a year or more to reach maturity.
Ecological Importance
Acts as an effective natural pest control agent by intercepting and consuming numerous household insect pests, helping to regulate local populations of flies, roaches, and other arthropods.
Conservation Status
Not evaluated by the IUCN, but highly secure, abundant, and widespread globally due to its successful adaptation to human-modified environments.
Interesting Facts
Despite their common name causing alarm, False Black Widows are remarkably timid and will readily play dead rather than bite. Their web silk is known for its remarkable tensile strength relative to its fine diameter.
Photography Tips
Use macro lenses with a ring flash or diffused external lighting to highlight the glossy texture of the abdomen without causing harsh shadows. Photograph from a dorsal or lateral angle to capture any faint pattern markings.
Identified: 2026-10-06T13:52:46.203430