False Black Widow, Cupboard Spider, Dark Comb-Footed Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded abdomen, comb-like setae on the fourth tarsus used for flinging silk over prey, and building irregular tangled cobwebs.
Physical Description
The spider has a distinctively bulbous, oval-to-globular abdomen that overhangs the smaller cephalothorax. The body surface has a smooth, somewhat glossy texture rather than heavy hairiness. The legs are relatively thin and long.
Size Estimate
Body length typically ranges from 6 to 10.5 mm for females, with males being slightly smaller at 4 to 6 mm. Leg span can reach up to 20 to 30 mm.
Coloration & Markings
Coloration ranges from deep brownish-purple to nearly black, sometimes with subtle lighter yellowish or reddish-cream markings, chevron patterns, or crescents on the upper surface of the abdomen, though these markings can be very faint or absent in older, darker specimens.
Web Type
Builds an irregular, messy tangle-web (cobweb) in dark, secluded areas such as corners of rooms, beneath furniture, inside outbuildings, and around crawlspaces or window frames.
Eye Arrangement
Consists of eight small eyes arranged in two slightly curved, roughly parallel rows of four across the front of the cephalothorax, typical of the cobweb spider family Theridiidae.
Leg Characteristics
Legs are thin, slender, and distinctly tapered, with faint brownish banding visible on some segments. They lack heavy spination but possess specialized comb-like structures on the hind tarsi.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom designed for subduing invertebrate prey. While a bite can cause localized pain, redness, and swelling, and occasionally mild systemic symptoms like malaise or headache, it is generally not medically significant for humans.
Medical Significance
Low medical significance. Bites are uncommon and rarely result in severe or lasting health issues. Thoroughly wash the bite area and apply a cold compress; seek medical attention if symptoms persist or if signs of a secondary bacterial infection appear.
Safety Recommendations
Avoid direct handling with bare hands when cleaning dark, undisturbed areas. If relocation is necessary, gently guide the spider into a container using a piece of cardstock and release it outdoors.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution found worldwide in temperate and subtropical regions. Highly synanthropic, commonly inhabiting human dwellings, cellars, garages, garden sheds, woodpiles, and sheltered outdoor crevices.
Behavior & Temperament
Timid, nocturnal, and non-aggressive. When disturbed, they typically retreat quickly into their web or curl up and play dead. Biting is rare and usually occurs only when accidentally trapped against human skin.
Diet & Prey
Feeds on a wide variety of crawling and flying insects, woodlice, and other spiders, occasionally subduing larger prey including other potentially dangerous spiders like true widows.
Seasonal Activity
Active year-round indoors where temperatures remain stable, with increased wandering and mating activity observed during late summer and autumn.
Description
Steatoda grossa, commonly known as the False Black Widow, is frequently mistaken for its more dangerous relative due to its dark, glossy, rounded appearance. However, it is a largely harmless and beneficial household resident that quietly manages pest insect populations from the corners of dark rooms and outbuildings.
Key Features
Glossy bulbous abdomen, lack of the distinctive red hourglass marking found on true widow spiders, dark purplish-brown coloration, and construction of an irregular cobweb in domestic structures.
Similar Species
True Black Widow (Latrodectus mactans) and other Latrodectus species, which possess a characteristic red or orange hourglass marking on the underside of the abdomen and typically lack the brownish-purple hue and subtle lighter chevrons of Steatoda grossa.
Life Cycle
Females produce brownish, papery egg sacs containing dozens to hundreds of eggs, hidden within the web retreat. Spiderlings hatch and disperse via ballooning or crawling. Adults can live for several years under favorable indoor conditions.
Ecological Importance
Acts as an effective natural pest controller in homes and gardens, regulating populations of nuisance insects like flies, roaches, and beetles.
Conservation Status
Not evaluated by the IUCN, but highly secure, abundant, and expanding its range globally due to human commerce and indoor habitat availability.
Interesting Facts
Despite their common name, False Black Widows have been documented successfully preying on true widow spiders by using their sticky silk and comb-footed techniques to overcome them.
Photography Tips
Photograph from a safe distance using macro settings or a macro lens. Ensure good lighting to highlight the glossy texture and subtle abdominal markings, and shoot from a top-down or profile angle to clearly capture body proportions.
Identified: 2026-08-30T14:58:05.303623