False Black Widow, Cupboard Spider, Cobweb Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae
Physical Description
The body is stout and bulbous with a shiny, smooth texture. The cephalothorax is relatively small compared to the large, rounded abdomen, which hangs over the rear. Females are noticeably larger and rounder than males.
Size Estimate
Body length typically ranges from 6 to 10.5 mm for females and 4 to 6 mm for males, with a leg span up to 20-30 mm.
Coloration & Markings
Deep brownish-purple to black coloration with pale yellowish or cream-colored markings, often featuring crescent or triangular shapes across the dorsal side of the abdomen. The skin has a distinct satin or greasy sheen.
Web Type
Tangle web or irregular cobweb constructed in dark, protected corners, usually near ground level or in undisturbed structural crevices.
Eye Arrangement
Eight eyes arranged in two horizontal rows of four, typical of the family Theridiidae, with small and generally uniform lateral eyes.
Leg Characteristics
Long, slender, tapering legs with minimal spination compared to wandering spiders, often held close to the body within the web structure.
Venom & Safety Information
Venom Information
Contains neurotoxic components (latrotoxin-like compounds in milder forms). Not life-threatening to humans, but envenomation can cause localized pain, blistering, and malaise.
Medical Significance
Minimally dangerous. Bites are rare and usually happen when the spider is accidentally trapped against skin. Symptoms are comparable to a mild hornet sting and generally resolve within days.
Safety Recommendations
Avoid direct handling with bare hands. Relocate individuals outside using a jar and stiff paper if found in living spaces. No special pest control is generally necessary.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, highly synanthropic. Frequently found in human dwellings, garages, sheds, under furniture, and around dark crevices worldwide.
Behavior & Temperament
Timid and non-aggressive. They prefer to retreat or play dead when disturbed, though females guarding egg sacs may bite defensively if directly compressed.
Diet & Prey
Generalist predator feeding on crawling and flying insects, woodlice, and occasionally other spiders caught in their cobweb.
Seasonal Activity
Active year-round indoors, with mating and increased wandering behavior typically peaking during the warmer late summer and autumn months.
Description
Steatoda grossa, commonly known as the false black widow, is often mistaken for its more dangerous relative due to its dark, bulbous abdomen and glossy finish. Despite this resemblance, it is a harmless and beneficial household resident that quietly manages indoor insect populations.
Key Features
Glossy bulbous abdomen, brownish-purple to black base color with pale geometric markings, lack of a red hourglass shape, and creation of an irregular cobweb.
Similar Species
Latrodectus species (Black Widows), which feature the distinct red hourglass marking on the underside of the abdomen and a less satin-like texture.
Life Cycle
Females produce brownish, papery egg sacs containing up to several hundred eggs. Spiderlings disperse via ballooning or crawling. Adults can live for several years under favorable conditions.
Ecological Importance
Serves as an effective natural pest control agent within human dwellings and outbuildings, preying on household pests like flies, roaches, and beetles.
Conservation Status
Not evaluated by the IUCN, but highly abundant and widespread globally due to successful adaptation to human environments.
Interesting Facts
False black widows are known to prey upon true black widows by invading their webs, utilizing sticky silk to subdue the more venomous spiders.
Photography Tips
Use macro lenses with diffused lighting to capture the subtle pale markings on the glossy abdomen without causing the spider to retreat into a dark crevice.
Identified: 2026-10-02T18:22:39.180456