Cupboard Spider, False Black Widow, Dark Cobweb Spider
Steatoda grossa
Family Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a globular abdomen, comb-like serrated bristles on the hind tarsi used to pull silk from the spinnerets, and typically building irregular tangle webs.
Physical Description
The spider has a glossy, bulbous, egg-shaped abdomen and a distinctively smaller, rounded cephalothorax. The overall body texture is smooth and shiny with a somewhat leather-like appearance. It lacks prominent hairs, giving it a sleek look compared to hairy wolf spiders or tarantulas.
Size Estimate
The body length of this adult or sub-adult specimen is approximately 6 to 10 millimeters, with a leg span of roughly 15 to 20 millimeters, fitting the typical medium range for the species.
Coloration & Markings
Features dark purplish-brown to almost black base coloration, often accented with lighter pale yellowish or cream-colored markings, chevron patterns, or spots on the dorsal side of the abdomen. The legs are a uniform brownish-orange without stark banding.
Web Type
Builds an irregular, sticky tangle web often referred to as a cobweb. These webs are typically constructed in dark, protected corners, crevices, around cupboards, and under furniture close to the ground.
Eye Arrangement
Consists of eight small eyes arranged in two horizontal rows of four, typical of the Theridiidae family, set closely together on a slightly raised tubercle on the front of the cephalothorax.
Leg Characteristics
Legs are moderately long, slender, and tapering, featuring a reddish-brown hue. They lack strong spination, but the hind legs possess a specialized comb of serrated bristles used for wrapping prey.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom designed for subduing invertebrate prey. While a bite can cause localized pain, redness, and occasionally mild systemic symptoms like malaise, it is generally not considered medically dangerous to humans.
Medical Significance
Low medical significance. Bites are rare and usually occur only when the spider is trapped directly against human skin. Symptoms mimic a mild sting or localized swelling, requiring basic first aid rather than emergency care.
Safety Recommendations
Avoid handling them with bare hands. If found inside, gently relocate the spider outdoors using a cup and a piece of card. Standard cleaning and sealing home entry points reduce encounters.
Habitat & Behavior
Habitat & Range
Found worldwide in temperate regions, frequently adapting to synanthropic environments such as houses, garages, sheds, and basements. Outdoors, they prefer dark cavities beneath rocks, logs, and bark.
Behavior & Temperament
Generally shy, non-aggressive, and nocturnal. When disturbed, they typically drop from their web and feign death or retreat rapidly into a dark crevice rather than bite.
Diet & Prey
Feeds primarily on crawling and flying insects, including woodlice, flies, cockroaches, and occasionally other spiders, using its sticky silk to immobilize prey before delivering a paralyzing bite.
Seasonal Activity
Active year-round indoors, but most commonly noticed during late summer and autumn when mature males wander in search of mates.
Description
Steatoda grossa, commonly known as the cupboard spider or false black widow, is a frequent household guest that often goes unnoticed in dark corners. With its glossy, bulbous abdomen and rich dark brown tones, it shares a superficial resemblance to true black widows but lacks the dangerous potency. As a master builder of messy cobwebs, it plays a quiet, beneficial role in keeping household insect populations in check without posing a threat to humans.
Key Features
Glossy, globular abdomen, dark brown to purplish coloration with faint pale geometric or chevron markings, lack of a red hourglass shape, and presence of a typical theridiid cobweb.
Similar Species
True Black Widow (Latrodectus species), which features a distinct red hourglass or red spots on the underside of a jet-black abdomen and lacks the brownish, patterned dorsal markings of Steatoda grossa.
Life Cycle
Females construct tough, brownish-white silk egg sacs containing up to several hundred eggs, which are hidden near the web. Spiderlings hatch after a few weeks, disperse, and undergo multiple molts before reaching maturity within a year.
Ecological Importance
Acts as an effective natural pest controller in domestic and semi-natural environments by regulating populations of nuisance insects like flies, beetles, and roaches.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and thriving globally due to successful human commensalism.
Interesting Facts
Despite being called the false black widow, Steatoda grossa can occasionally prey on true black widows by invading their webs, carefully avoiding the sticky lines, and subduing them with specialized silk wrapping.
Photography Tips
Use macro lenses with good side-lighting to highlight the glossy texture of the abdomen and any faint geometric markings. Maintain a steady hand and shoot from a slightly elevated angle.
Identified: 2026-09-21T03:40:30.216445