False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Family Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded abdomen, comb-like serrated bristles on the fourth tarsus used for flinging silk over prey, and typically building irregular, messy tangle webs.
Physical Description
The spider has a bulbous, glossy, teardrop-to-oval shaped abdomen and a compact, robust cephalothorax. It has a smooth, satin-like exoskeleton without heavy hairiness. The body proportions feature a larger abdomen relative to the cephalothorax, typical of comb-footed spiders.
Size Estimate
Body length is approximately 6 to 10 millimeters, with a leg span of roughly 15 to 20 millimeters. Based on the proportions in the image, this is a small adult female or a well-developed juvenile.
Coloration & Markings
Deep brownish-purple to nearly black base coloration with subtle lighter pale or yellowish markings on the dorsal abdomen, sometimes forming chevron or crescent patterns. The legs are generally uniform brown without distinct banding.
Web Type
Builds an irregular, sticky tangle web or cobweb, typically constructed in dark, undisturbed corners, crevices, near ground level, or around human habitations like sheds and garages.
Eye Arrangement
Features eight small eyes arranged in two horizontal rows of four, typical of the Theridiidae family, all generally uniform in size with dark bases.
Leg Characteristics
Legs are moderately slender, relatively long, and taper toward the ends. They lack prominent spination or strong banding, and the spider typically adopts a compact posture when resting in its web.
Venom & Safety Information
Venom Information
Possesses a neurotoxic venom, but it is considerably less potent than that of true widow spiders (Latrodectus). Envenomation is rarely medically significant for humans.
Medical Significance
Low medical significance. A bite may cause localized pain, mild swelling, redness, and occasionally general malaise or mild flu-like symptoms that subside within 24 hours. Severe systemic reactions are extremely rare. Clean the wound and apply a cold compress.
Safety Recommendations
Avoid handling spiders with bare hands when cleaning dark corners or moving stored items. If relocation is necessary, gently guide the spider into a container using a piece of card. Standard first aid involves antiseptic washing and cold packs.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, widely found across North America, Europe, and other temperate regions. Prefers dark, humid microhabitats such as under rocks, bark, woodpiles, and inside human structures like basements, cellars, and crawlspaces.
Behavior & Temperament
Generally non-aggressive, timid, and nocturnal. It tends to retreat, curl up, or drop from its web when disturbed rather than bite. Bites usually only occur if the spider is directly trapped or pressed against human skin.
Diet & Prey
Feeds primarily on insects, woodlice, and occasionally other spiders. It uses its sticky tangle web to trap crawling or flying prey, subsequently subduing them with rapid silk wrapping and venom injection.
Seasonal Activity
Active year-round indoors, but most visible during late summer and autumn when mature males wander in search of mates. Overwinters safely protected within structures or sheltered crevices.
Description
The False Black Widow (Steatoda grossa) is a frequent companion in human dwellings, often mistaken for its more dangerous relative due to its dark, glossy appearance and bulbous abdomen. While unassuming and largely beneficial as a pest controller, this nocturnal hunter quietly tends its messy cobweb in forgotten corners, showcasing the remarkable adaptability of the cobweb spider family.
Key Features
Glossy, bulbous dark brown to purplish abdomen; absence of bright red hourglass markings; irregular cobweb construction; absence of heavy leg spination.
Similar Species
True Black Widow (Latrodectus mactans), which features a distinctive red hourglass marking on the ventral abdomen and a jet-black glossy finish. Other Steatoda species like Steatoda triangulosa (Triangle Weaver) which features distinct geometric patterns.
Life Cycle
Females produce papery, brownish egg sacs containing dozens to hundreds of eggs, often hanging within the web. Spiderlings hatch after a few weeks, undergo multiple molts as they grow, and can live for several years in favorable conditions.
Ecological Importance
Acts as an effective natural predator of household and garden pests, helping control insect populations and contributing to the stability of local arthropod food webs.
Conservation Status
Not evaluated by the IUCN, but populations are secure, abundant, and widely distributed globally due to high adaptability to human-altered environments.
Interesting Facts
Despite their ominous common name, false black widows are frequently beneficial pest controllers that help reduce populations of crawling insects and other spiders around homes.
Photography Tips
Use macro lenses with good side lighting to highlight the glossy texture and subtle dorsal patterns of the abdomen. Maintain a safe macro distance and photograph from above or the side to clearly capture the body proportions.
Identified: 2026-09-22T11:43:53.287082