Cupboard Spider, False Black Widow, Dark Cobweb Spider
Steatoda grossa
Family Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded, bulbous abdomen, comb-like setae on the fourth tars segment, and building irregular tangle webs.
Physical Description
The spider has a compact body with a glossy, oval-shaped abdomen and a smaller, rounded cephalothorax. The exoskeleton has a smooth, satin-like finish rather than being heavily hairy, and females are typically larger and more robust than males.
Size Estimate
Body length ranges from 6 to 10.5 mm for females and 4 to 6 mm for males, with a leg span of approximately 20 to 30 mm. This specimen appears to be an adult or sub-adult.
Coloration & Markings
Deep brownish-purple to black base coloration, often featuring pale yellowish, cream, or whitish markings in a crescent or triangular pattern on the anterior dorsal abdomen. The legs are generally a uniform dark brown or reddish-brown.
Web Type
Constructs an irregular, messy tangle web, commonly known as a cobweb. These webs are typically built in dark, sheltered areas close to the ground, inside corners, crevices, or around structural fixtures.
Eye Arrangement
Consists of eight small eyes arranged in two parallel, slightly curved rows of four. The lateral eyes are typically touching or closely grouped, a classic diagnostic feature of the Theridiidae family.
Leg Characteristics
Legs are moderately long and slender, tapering toward the ends, with faint darker banding visible in some individuals. They feature sparse spines and lack specialized heavy brush-like scopulae, maintaining a typical cobweb spider stance.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom designed to immobilize invertebrate prey. While a bite can cause localized pain, mild swelling, and occasional systemic symptoms such as nausea or headache, it is generally not considered medically dangerous to humans.
Medical Significance
Low medical significance. Bites are uncommon due to the spider's shy nature and only occur if pressed directly against human skin. Symptoms usually resolve within a day without specialized medical treatment.
Safety Recommendations
Minimize clutter in dark corners, wear gloves when handling stored items or firewood, and use a glass and piece of paper to safely capture and relocate the spider outdoors if found inside.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution found worldwide in temperate and subtropical regions. Frequently inhabits human dwellings, outbuildings, garages, woodpiles, and dark crawlspaces, preferring low, undisturbed areas with high humidity.
Behavior & Temperament
Docile, timid, and non-aggressive. It relies on its web to detect vibrations from prey and will typically retreat, curl into a ball, or drop from its web when disturbed rather than bite.
Diet & Prey
Feeds primarily on crawling and flying insects, including woodlice, flies, beetles, cockroaches, and occasionally other spiders. Prey is subdued using sticky silk lines before being bitten and immobilized.
Seasonal Activity
Active year-round indoors, with peak visibility and mating activity occurring during the warmer summer and autumn months when wandering males search for females.
Description
Steatoda grossa, commonly known as the cupboard spider or false black widow, is a frequent human co-inhabitant. With its glossy, bulbous abdomen and dark coloration, it is often mistaken for its more dangerous relative, the true black widow, but it is entirely docile and beneficial for pest control around homes.
Key Features
Glossy bulbous abdomen, dark brownish-purple coloration, contrasting pale cream-colored chevron or crescent markings near the front of the abdomen, and an absence of a red hourglass shape.
Similar Species
True Black Widow (Latrodectus species), which features a distinctive red hourglass marking on the underside of the abdomen; Steatoda nobilis (Noble False Widow), which has a more intricate skull-like or angular pattern.
Life Cycle
Females produce papery, brownish egg sacs containing up to several hundred eggs, which are guarded within the web. Spiderlings hatch, disperse locally, and undergo multiple molts over a lifespan that can reach up to several years for females.
Ecological Importance
Serves as an effective natural predator of household pests, helping to control populations of flies, roaches, and other insects within domestic and outbuilding environments.
Conservation Status
Not evaluated by the IUCN, but populations are secure, highly adaptable, and thriving globally due to their association with human habitations.
Interesting Facts
Despite being called the 'false black widow,' Steatoda grossa can actively prey on true black widows by invading their webs, using its superior silk application to subdue the more venomous species.
Photography Tips
Use macro lenses with good side lighting to highlight the glossy texture and subtle pale markings on the abdomen. Photograph against a neutral background while the spider is stationary in its web.
Identified: 2026-10-10T07:48:30.769188