False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae
Physical Description
The spider has a bulbous, glossy, globose abdomen and a smaller cephalothorax. The exoskeleton is smooth and leather-like. Females are significantly larger and rounder than males, which have narrower abdomens and longer legs.
Size Estimate
Body length ranges from 6 to 10.5 mm for females and 4 to 6 mm for males, with a leg span up to 20 to 30 mm.
Coloration & Markings
Deep brownish-purple to blackish coloration, often featuring faint, pale yellowish or cream-colored markings, chevrons, or a crescent shape on the dorsal side of the abdomen. Some specimens may have reddish-brown tones.
Web Type
Irregular tangle web (cobweb) constructed in dark, undisturbed corners, crevices, or near ground level.
Eye Arrangement
Eight small eyes arranged in two rows of four, typical of the Theridiidae family, with lateral eyes touching or closely spaced.
Leg Characteristics
Thin, moderately long legs lacking heavy spination, often displaying faint darker banding. They possess a comb of serrated bristles on the tarsus of the fourth pair of legs used for flinging silk over prey.
Venom & Safety Information
Venom Information
Neurotoxic venom of mild potency relative to humans. Envenomation is not life-threatening but can cause localized pain, swelling, and occasionally mild systemic symptoms.
Medical Significance
Minimally significant. Bites are rare and usually only occur when the spider is pressed directly against the skin. Symptoms resemble a mild bee sting, though rare severe reactions (steatodism) can cause localized blistering and malaise.
Safety Recommendations
Avoid handling with bare hands. If found inside, gently capture under a glass or plastic container and release outdoors. Wear gloves when cleaning out dark, undisturbed storage spaces.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution worldwide in temperate regions. Commonly found indoors in basements, garages, under furniture, and outdoors under rocks, bark, and in dark crevices.
Behavior & Temperament
Docile and non-aggressive. They spend most of their time hanging upside down in their webs and retreat when disturbed, only biting if trapped against skin.
Diet & Prey
Insects and other arachnids, including woodlice and occasionally other spiders, captured by entanglement in the sticky cobweb.
Seasonal Activity
Active year-round indoors, with increased movement and mating activity typically observed during late summer and autumn.
Description
Steatoda grossa, commonly known as the False Black Widow, is a frequent indoor companion that often startles homeowners due to its superficial resemblance to dangerous widow spiders. With its glossy, rounded dark body and preference for quiet corners, it is a master pest controller quietly managing insect populations around human dwellings.
Key Features
Glossy bulbous abdomen, lack of a true red hourglass marking, dark purple-brown coloration, and construction of an irregular cobweb in a dark corner.
Similar Species
Latrodectus species (True Widow Spiders), which possess a distinct red hourglass or bright warning spots on the underside of the abdomen, whereas Steatoda grossa lacks these vivid markings.
Life Cycle
Females produce several spherical or oval silk egg sacs containing up to 200 eggs each. Spiderlings disperse via ballooning or crawling after hatching. Lifespan can be several years for females.
Ecological Importance
Serves as an effective natural pest controller in human habitations and natural environments by consuming flies, cockroaches, and other nuisance insects.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and frequently expanding through human commerce.
Interesting Facts
Despite being called the False Black Widow, Steatoda species sometimes successfully prey on true widow spiders by invading their webs and wrapping them in silk.
Photography Tips
Use macro lenses with a ring flash or side lighting to capture the glossy texture and subtle dorsal markings without disturbing the spider in its web retreat.
Identified: 2026-08-21T17:10:29.129631