False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
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 building irregular, tangled three-dimensional webs.
Physical Description
The spider has a glossy, bulbous, egg-shaped abdomen and a relatively compact cephalothorax. The body texture is smooth and shiny with minimal prominent hair, giving it a somewhat sleek appearance. The specimen shown appears to be a juvenile or subadult based on its smaller proportions and prominent patterning.
Size Estimate
Body length is estimated around 6 to 10 millimeters, with a leg span of approximately 15 to 22 millimeters. This falls into the smaller to medium range for the species, characteristic of a younger or male adult specimen.
Coloration & Markings
The carapace and legs are a dark reddish-brown to blackish tone. The rounded abdomen features distinct pale yellowish or cream-colored band markings and spots against a dark brownish-red background, which is typical for younger or patterned Steatoda species.
Web Type
Builds an irregular, tangled web commonly referred to as a cobweb, typically constructed in dark, undisturbed corners, crevices, or around man-made structures like lamps, basements, and window frames.
Eye Arrangement
Has eight small eyes arranged in two horizontal rows of four, typical of the Theridiidae family, positioned on the front of the rounded cephalothorax.
Leg Characteristics
Legs are moderately long and thin, featuring distinct dark banding or rings along the segments, which contrast with lighter brown or reddish base tones. They are held close to the body or spread within the confines of the tangle web.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom designed to subdue insect prey. While venomous, it is generally considered mild compared to true widows.
Medical Significance
Not medically significant to humans. A bite can cause minor local pain, redness, and swelling, but severe systemic symptoms are rare and typically resolve without professional medical intervention.
Safety Recommendations
Keep living areas clean and seal entry points. If found inside, it can be safely relocated outside using a cup and a piece of paper. Wear gloves if clearing old webs in dark corners.
Habitat & Behavior
Habitat & Range
Found globally in temperate regions, frequently associated with human habitations, outbuildings, basements, garages, and dark crevices indoors, as well as under rocks and bark outdoors.
Behavior & Temperament
Generally non-aggressive and timid. They remain in or near their retreat webs most of the time, dropping or retreating rapidly when disturbed rather than striking out.
Diet & Prey
Feeds primarily on crawling and flying insects, including woodlice, flies, beetles, and occasionally other spiders, which become entangled in the sticky threads of the cobweb.
Seasonal Activity
Active year-round indoors, with increased visibility and wandering behavior during late summer and autumn when searching for mates.
Description
The False Black Widow (Steatoda grossa) is a frequent indoor companion that often startles homeowners due to its dark, glossy appearance and resemblance to dangerous widow spiders. With its bulbous, patterned abdomen and slender banded legs, this skillful cobweb weaver quietly patrols the darker corners of human structures, providing natural pest control against household insects.
Key Features
Glossy, bulbous abdomen with pale geometric markings or bands, dark reddish-brown to blackish glossy cephalothorax, and banded legs without the red hourglass marking.
Similar Species
True Black Widow (Latrodectus species), which lacks the pale dorsal banding and features an unmistakable red hourglass on the underside of the abdomen.
Life Cycle
Females construct tough silken egg sacs containing numerous eggs, attaching them near the web. Spiderlings disperse shortly after hatching, molting several times to reach maturity over a lifespan of a year or more.
Ecological Importance
Serves as an effective predator of household pests and common insects, helping to naturally regulate insect populations within human dwellings and surrounding habitats.
Conservation Status
Not threatened; secure and widespread globally, often thriving in close proximity to human settlements.
Interesting Facts
Despite sharing a common name and a somewhat similar silhouette with black widows, Steatoda species belong to a different genus entirely and their bites are significantly less severe.
Photography Tips
Use macro lenses with adequate lighting or a diffuser to capture the glossy texture and subtle pale banding on the abdomen without disturbing the spider in its web.
Identified: 2026-08-25T23:37:12.338578