False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a generally globose abdomen, comb-like serrated bristles on the fourth tarsus used for flinging silk over prey, and often building irregular tangle webs.
Physical Description
The spider has a glossy, bulbous, egg-shaped abdomen and a distinctively smaller, rounded cephalothorax. The overall texture is smooth and shiny rather than hairy, with visible sexual dimorphism where females are noticeably larger and rounder 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 reaching up to 20 to 30 mm. This specimen appears to be an adult or subadult female.
Coloration & Markings
Deep purplish-brown to blackish base coloration with pale yellowish, cream, or greyish markings on the dorsal abdomen, often forming geometric patterns, crescents, or a series of chevron-like lines. The legs are a lighter reddish-brown, sometimes showing faint banding.
Web Type
Builds an irregular, three-dimensional tangle web commonly known as a cobweb. These webs are constructed in dark, sheltered locations such as corners, crevices, under furniture, or in outbuildings and woodpiles.
Eye Arrangement
Eight small eyes arranged in two horizontal rows of four, typical of the Theridiidae family, set closely together on a slightly elevated region of the cephalothorax.
Leg Characteristics
Long, slender legs with minimal spination compared to wandering spiders, featuring a distinct comb-like row of serrated setae on the hind tarsi. Legs are typically spread out flat against the surface when resting in the web or on a wall.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom (specifically latrotoxin-like compounds, though much milder than true widow spiders). Potency relative to humans is low, generally causing localized pain and minor swelling.
Medical Significance
Not considered dangerously venomous to humans. Bites are rare and usually occur only when the spider is trapped against the skin. Symptoms may include localized burning, redness, and mild malaise lasting a few hours, akin to a wasp sting.
Safety Recommendations
Avoid handling with bare hands; if removal is necessary, use a glass and a piece of card to safely relocate the spider outside. Wear gloves when cleaning out dark, undisturbed storage areas.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found worldwide in temperate and subtropical regions including North America, Europe, and parts of Australia. Prefers dark, humid microhabitats around human dwellings, basements, garages, hollow trees, and rock crevices.
Behavior & Temperament
Timid and non-aggressive, relying on retreat into its web or dropping to the ground when disturbed. Nocturnal hunters that spend most of their time hanging upside down in their webs waiting for prey.
Diet & Prey
Feeds primarily on crawling and flying insects including roaches, woodlice, earwigs, flies, and occasionally other spiders. Uses strong silk to hoist heavier prey items up into the web.
Seasonal Activity
Active year-round indoors, but mating and peak foraging activity occur primarily during late summer and autumn when mature males wander in search of females.
Description
The False Black Widow is frequently mistaken for its more dangerous relative due to its glossy, dark, globular abdomen, but it is a harmless and beneficial household resident. Thriving in dark corners and quiet basements, it quietly manages pest populations with its sticky, tangled webs. While unassuming, its rich mahogany-to-black tones paired with pale crescent markings give it a subtle, elegant beauty.
Key Features
Glossy, bulbous dark abdomen with pale geometric markings or crescents, lack of a red hourglass shape, and a noticeably shiny texture without dense hair.
Similar Species
True Black Widow (Latrodectus mactans) - distinguished by the presence of a bright red hourglass marking on the underside of the abdomen and a jet-black matte finish rather than glossy purple-brown.
Life Cycle
Females produce several spherical silk egg sacs containing up to 200 eggs each during the warmer months. Spiderlings disperse via ballooning or crawling. Molting occurs multiple times before reaching maturity, with a potential lifespan of several years for females.
Ecological Importance
Acts as an effective biological control agent by consuming common household pests and insects, helping regulate populations of nuisance species in and around human habitations.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and frequently expanding alongside human development due to artificial habitat creation.
Interesting Facts
False Black Widows have been known to occasionally prey on true black widows and other potentially dangerous spiders that wander into their webs, effectively serving as natural pest control against more venomous species.
Photography Tips
Use a macro lens with good side-lighting to capture the glossy texture of the abdomen and the pale dorsal markings. Maintain a steady hand or use a tripod, as the spider will remain still if undisturbed in a defensive or resting posture.
Identified: 2026-09-01T17:31:08.996971