Cupboard Spider, False Black Widow, Dark Cobweb 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, and typically building irregular tangle webs.
Physical Description
The spider has a bulbous, glossy, egg-shaped abdomen that overhangs the cephalothorax slightly. The cephalothorax is compact and robust. The overall texture appears smooth and somewhat shiny rather than heavily hairy. Females are typically larger and more robustly proportioned than males.
Size Estimate
Body length ranges from 6 to 10.5 mm for females and 4 to 6 mm for males, with a total leg span reaching up to roughly 20 to 30 mm. This specimen appears to be an adult or sub-adult based on body proportions.
Coloration & Markings
Deep purplish-brown to brownish-black base coloration, sometimes featuring subtle lighter yellowish or grayish markings, chevrons, or crescents on the upper abdomen, though older individuals can appear uniformly dark and glossy.
Web Type
Builds an irregular, messy tangle web, commonly known as a cobweb, typically constructed in dark, undisturbed areas close to ground level or in corners of rooms, garages, and cupboards.
Eye Arrangement
Eight small eyes arranged in two slightly curved, roughly parallel horizontal rows of four across the front of the cephalothorax, typical of the family Theridiidae.
Leg Characteristics
Legs are moderately long, sturdy, and tapering, possessing distinct reddish-brown tones. They generally lack prominent spination compared to hunting spiders and are often held close to or flattened against surfaces when resting.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom designed for invertebrate prey. While sometimes called the false widow, its venom is significantly less potent than that of true black widows (Latrodectus species).
Medical Significance
Low medical significance. A bite can cause mild localized pain, redness, and swelling lasting a few hours. Systemic effects are rare and generally mild, unlike the severe reactions associated with Latrodectus bites.
Safety Recommendations
Wear gloves when cleaning dark, undisturbed storage areas. If relocation is desired, gently guide the spider into a container using a piece of cardstock. Bites are rare and easily prevented by avoiding direct handling.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found worldwide in temperate and subtropical regions. Highly synanthropic, commonly inhabiting human-made structures, basements, crawl spaces, sheds, under furniture, and outdoor dark crevices.
Behavior & Temperament
Timid, docile, and non-aggressive. It hangs upside down in its web and retreats rapidly when disturbed. It rarely bites unless directly trapped or squeezed against human skin.
Diet & Prey
Feeds on a wide variety of crawling and flying insects, including woodlice, flies, mosquitoes, beetles, and other spiders. It uses sticky silk threads to subdue prey before delivering a paralyzing venom bite.
Seasonal Activity
Active year-round indoors, with increased visibility and wandering behavior during warmer months and mating seasons.
Description
Steatoda grossa, widely known as the cupboard spider or false black widow, is a frequent indoor companion in homes around the globe. With its glossy, bulbous, dark body and preference for quiet corners, it plays a silent yet effective role in keeping household insect populations in check while remaining inherently shy toward humans.
Key Features
Glossy, bulbous, dark brown to black abdomen; lack of a red hourglass marking; robust and compact body shape; habit of constructing messy cobwebs in dark indoor spaces.
Similar Species
True Black Widows (Latrodectus species), which feature a distinct red hourglass or red spots on the underside of the abdomen. Steatoda grossa lacks any bright red or orange warning markings.
Life Cycle
Females produce papery, brownish silk egg sacs containing up to several hundred eggs, hidden near the web. Spiderlings disperse via ballooning or crawling after hatching. They molt multiple times and can live for several years.
Ecological Importance
Serves as an effective natural pest controller in domestic and peri-domestic environments by reducing populations of nuisance insects and other arthropods.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and frequently expanding due to close association with human habitats.
Interesting Facts
Despite sharing a superficial resemblance and the 'false widow' moniker with Latrodectus species, Steatoda grossa is frequently mistaken for dangerous spiders despite being largely harmless and beneficial around homes.
Photography Tips
Photograph from a side or top-down angle using macro settings and diffuse lighting to capture the glossy texture and subtle abdominal markings without disturbing the spider.
Identified: 2026-08-21T02:31:13.180444