False Black Widow, Cobweb Spider, cupboard spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a generally globular abdomen, combed setae on the fourth tarsus for pulling silk, and often small, delicate webs.
Physical Description
The spider has a glossy, bulbous, oval-shaped abdomen that overhangs the cephalothorax, and relatively short, tapering legs. The body surface appears smooth and somewhat shiny, with no prominent spines, characteristic of many cobweb spiders.
Size Estimate
Body length ranges from 6 to 10.5 mm for females, with a leg span reaching up to roughly 20 to 25 mm. This specimen appears to be an adult female due to the large, rounded, shiny abdomen.
Coloration & Markings
Deep purplish-brown to blackish base coloration with pale yellowish or cream markings. These markings often form subtle chevron or crescent patterns across the dorsal side of the abdomen, though some individuals may be almost uniformly dark.
Web Type
Builds an irregular, tangled web commonly known as a cobweb, constructed in dark, protected corners, crevices, under furniture, or near ground level.
Eye Arrangement
Consists of eight small eyes arranged in two parallel rows of four, typical of the Theridiidae family, with lateral eyes often touching or closely grouped.
Leg Characteristics
Legs are relatively thin, moderately short, dark brown, and lack prominent spines, featuring subtle darker banding and specialized comb-like claws on the rear tarsi.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom, though it is significantly milder than that of true widow spiders (Latrodectus spp.). Envenomation rarely causes severe systemic effects in humans.
Medical Significance
Minor medical significance. A bite can cause localized pain, redness, and swelling, occasionally accompanied by mild systemic symptoms like malaise or headache, but it is not considered dangerous or life-threatening.
Safety Recommendations
Avoid direct handling with bare hands when cleaning dark corners or basements. If found inside, relocate outdoors using a glass and a piece of card. First aid for bites includes washing the area with soap and water and applying a cold compress.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, frequently found in temperate regions worldwide. Prefers dark, humid domestic environments such as basements, garages, under rocks, and around human habitations.
Behavior & Temperament
Generally shy, non-aggressive, and nocturnal. They remain secluded in their webs and retreat when disturbed, only biting defensively if trapped or firmly pressed against human skin.
Diet & Prey
Feeds primarily on crawling insects, woodlice, and occasionally other spiders trapped in its sticky cobweb.
Seasonal Activity
Active year-round indoors, with peak visibility and mating activity typically occurring during the late summer and autumn months.
Description
The false black widow (Steatoda grossa) is a frequent household guest often mistaken for its more dangerous relative, the true black widow. With its glossy, rounded, dark brown abdomen and subtle pale markings, it quietly constructs messy webs in dark corners, acting as a natural pest control agent against crawling insects.
Key Features
Glossy, bulbous, dark brown to purplish abdomen, pale yellowish chevron or triangular markings on the upper abdomen, lack of a red hourglass shape, and a tangled cobweb structure.
Similar Species
True Black Widow (Latrodectus spp.) - distinguished by the presence of a distinct red hourglass marking underneath the abdomen and a jet-black, velvety texture rather than glossy brown.
Life Cycle
Females produce spherical silk egg sacs containing dozens to hundreds of eggs, guarding them until spiderlings hatch. They undergo multiple molts to reach maturity and can live for several years.
Ecological Importance
Serves as an effective natural predator of common household and garden pests, helping to regulate populations of insects like roaches, beetles, and flies.
Conservation Status
Not evaluated by the IUCN, but highly abundant, widespread, and stable globally due to its adaptability to human structures.
Interesting Facts
Despite their ominous common name, false widows are exceptionally docile and their venom, while causing localized discomfort, is incapable of causing the severe necrotic or systemic syndromes associated with dangerous spiders.
Photography Tips
Use macro lenses with adequate side-lighting to highlight the glossy texture and subtle pale dorsal patterns of the abdomen, while maintaining a safe, stable distance.
Identified: 2026-09-28T04:14:07.426151