False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded, bulbous abdomen, comb-like setae on the fourth tarsus for pulling silk, and the construction of irregular tangle webs.
Physical Description
The spider features a robust, glossy appearance with a rounded, bulbous abdomen and a smaller, oval cephalothorax. The body is relatively smooth with minimal hairiness compared to wolf spiders or tarantulas. The specimen shows typical theridiid proportions, with the abdomen noticeably larger than the front section.
Size Estimate
Body length ranges typically from 6 to 10.5 mm for females, with males slightly smaller at 4 to 6 mm. Leg span is roughly 2 to 3 cm. This specimen appears to be an adult or sub-adult based on body proportions.
Coloration & Markings
Deep purplish-brown to black coloration, sometimes with a reddish-brown tinge. The abdomen often features subtle lighter grey, yellowish, or whitish triangular or crescent-shaped markings, though these can be faint or absent in very dark individuals.
Web Type
Builds an irregular, messy tangle web often referred to as a cobweb. These webs are constructed in dark, protected corners, crevices, near ground level, or around human structures like basements and garages.
Eye Arrangement
Eight small eyes arranged in two slightly curved horizontal rows of four across the front of the cephalothorax, typical of the family Theridiidae.
Leg Characteristics
Long, slender legs with distinct brownish coloration, generally lacking prominent spines or bands, though they may have subtle darker rings at the joints. Legs are often held close to the body or spread within the tangle web.
Venom & Safety Information
Venom Information
Neurotoxic venom, but significantly milder than that of true widow spiders (Latrodectus). Envenomation in humans is rare and typically results in localized pain, redness, and mild swelling.
Medical Significance
Low medical significance. While bites can cause mild localized discomfort and occasionally systemic symptoms like malaise or headache (steatodism), they are generally not dangerous and do not require emergency medical intervention unless an allergic reaction occurs.
Safety Recommendations
Wear gloves when clearing dark, undisturbed storage areas or woodpiles. If found indoors, gently guide the spider into a container using a piece of card and release it outdoors.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found worldwide in temperate regions including North America, Europe, and parts of Australia. Prefers dark, humid, sheltered microhabitats such as woodpiles, under rocks, hollow trees, and inside human dwellings.
Behavior & Temperament
Nocturnal and reclusive, spending most of its time hidden in its retreat or web. Non-aggressive, biting only when trapped or accidentally squeezed against human skin.
Diet & Prey
Feeds primarily on crawling insects, woodlice, and other spiders. Uses its sticky cobweb to trap prey and employs rapid wrapping techniques to subdue larger insects before biting.
Seasonal Activity
Active year-round indoors, with increased movement and mating activity observed during late summer and autumn.
Description
The False Black Widow (Steatoda grossa) is a frequent visitor to human dwellings, often mistaken for its dangerous relative, the Black Widow. With its glossy dark body and rounded silhouette, it is a master of quiet persistence, maintaining orderly cobwebs in forgotten corners where it efficiently manages local insect populations.
Key Features
Rounded, bulbous dark abdomen; lack of a red hourglass marking; purplish-brown to black coloration; creation of irregular tangle webs in dark corners.
Similar Species
True Black Widow (Latrodectus spp.), which possesses a distinct red hourglass mark on the underside of the abdomen and jet-black glossy coloration. Other Steatoda species like Steatoda triangulosa.
Life Cycle
Females produce spherical, papery silk 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
Acts as an effective natural pest control agent in and around homes, reducing populations of roaches, earwigs, and other household insects.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and frequently expanding due to human habitation.
Interesting Facts
Despite their ominous common name, false widows frequently prey on true widows and other dangerous spiders when they enter their webs, successfully subduing them.
Photography Tips
Use macro lenses with a ring flash or diffuser to highlight the glossy texture of the abdomen without creating harsh glares. Photograph from above to capture dorsal markings clearly.
Identified: 2026-08-23T00:26:17.078402