False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a globular abdomen, comb-like setae on the fourth tarsus used for flinging silk over prey, and typically building irregular, tangled three-dimensional webs.
Physical Description
The spider features a bulbous, glossy, globular abdomen and a smaller, elongated cephalothorax. The exoskeleton has a smooth, shiny texture, almost resembling polished leather. There is clear sexual dimorphism, with females being significantly larger, rounder, and bulkier than males, which have narrower abdomens and longer legs relative to their body size.
Size Estimate
Body length ranges from 6 to 10.5 mm for adult females (males are slightly smaller, around 4 to 6 mm), with a total leg span reaching approximately 20 to 30 mm. This specimen appears to be an adult female based on the large, rounded, shiny abdomen.
Coloration & Markings
Deep dark brown to purplish-black or reddish-brown base coloration. Unlike true black widows, it lacks a red hourglass mark, but it may display subtle pale yellowish or whitish markings, crescent shapes, or faint chevrons on the dorsal abdomen, especially in younger specimens or after recent molts.
Web Type
Builds an irregular, messy tangle web, commonly known as a cobweb. These webs are typically constructed in dark, sheltered areas such as corners, under furniture, in sheds, or near ground level, consisting of sticky, crisscrossing silk threads designed to intercept crawling and flying insects.
Eye Arrangement
Has eight small, bead-like eyes arranged in two parallel, horizontal rows of four each (anterior and posterior lateral pairs joined at the bases, and four median eyes). This is a standard arrangement for the family Theridiidae.
Leg Characteristics
Legs are relatively slender, moderately long, and taper toward the ends, matching the dark reddish-brown body color. They generally lack prominent spines but possess specialized comb-like structures (comb-feet) on the final segments of the hind legs for manipulating silk.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom (latrotoxin-like components), but it is significantly less potent than that of true widow spiders (Latrodectus). While a bite is painful, it is generally not life-threatening to humans.
Medical Significance
Minor medical significance. A bite causes localized pain, redness, and swelling. In rare cases, minor systemic symptoms like mild nausea, headache, or malaise can occur (steatodism). Thoroughly clean the wound and apply a cold compress. Seek medical attention if symptoms worsen or show signs of secondary infection.
Safety Recommendations
Wear gloves when cleaning out dark, undisturbed areas like woodpiles, basements, or sheds. If relocation is needed, gently guide the spider into a container using a piece of cardstock and release it outdoors.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found worldwide in temperate and warm regions, including North America, Europe, Australia, and parts of South America. Prefers dark, humid, sheltered microhabitats around human structures, including basements, crawlspaces, garages, sheds, stone walls, and dense garden vegetation.
Behavior & Temperament
Reclusive, nocturnal, and non-aggressive. They spend most of their time stationary in their webs. They rely on vibration sensing to detect prey or threats. When disturbed, they typically retreat quickly into a crevice or drop out of the web, only biting if directly pressed against human skin.
Diet & Prey
Feeds primarily on crawling and flying insects, including flies, beetles, woodlice, cockroaches, and other spiders. They use their sticky cobwebs to trap prey and then quickly wrap them in additional silk before delivering a paralyzing bite.
Seasonal Activity
Active year-round indoors and in sheltered outdoor areas, but most commonly encountered during late summer and autumn when males wander in search of mates and populations peak.
Description
The False Black Widow is frequently mistaken for its dangerous relative, but it is a gentle and beneficial resident of dark corners and sheds. With its glossy, dark, button-like abdomen, it quietly manages pest populations around homes, using its chaotic web to catch unsuspecting intruders.
Key Features
Glossy, globular dark brown to purplish abdomen; absence of a red hourglass marking; irregular cobweb construction; slender, unbanded dark legs; preference for dark, sheltered structural habitats.
Similar Species
True Black Widow (Latrodectus spp.), which features a distinctive bright red hourglass on the underside of the abdomen and lacks pale dorsal markings; Steatoda triangulosa (Triangle Spider), which has distinct triangular patterns on the abdomen.
Life Cycle
Females construct tough, paper-like silk egg sacs containing up to several hundred eggs and guard them closely. Spiderlings emerge after a few weeks, undergo multiple molts as they grow, and can live for several years, with females living longer than males.
Ecological Importance
Acts as an effective natural pest controller by reducing populations of household pests, agricultural insects, and disease vectors. They serve as a food source for larger predators like birds, small reptiles, and larger arthropods.
Conservation Status
Not evaluated by the IUCN, but populations are secure, abundant, and expanding globally due to human-mediated transport and urbanization.
Interesting Facts
False black widows are known to occasionally prey on true black widows and other potentially hazardous spiders that wander into their webs. Their bite is the most frequently reported spider bite requiring medical consultation in parts of Europe and the UK.
Photography Tips
Use macro lenses with good lighting (diffused flash to prevent harsh glare off the glossy exoskeleton). Shoot from the side or slightly above to capture the dome-like abdominal shape and any faint dorsal markings while maintaining a safe distance.
Identified: 2026-09-12T06:40:07.529205