False Black Widow, Cobweb Spider, Dark comb-footed spider
Steatoda grossa
Family Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a comb-like row of setae on the tarsus of the fourth leg used to pull silk from the spinnerets.
Physical Description
The spider has a bulbous, glossy, globular abdomen that overhangs the cephalothorax slightly. It has a smooth, shiny texture without heavy hairs, giving it a somewhat sleek appearance. The cephalothorax is compact and oval-shaped.
Size Estimate
Body length typically ranges from 6 to 10.5 mm for females, with males slightly smaller at 4 to 6 mm. Total leg span is roughly 20 to 30 mm.
Coloration & Markings
Deep purplish-brown to black coloration with subtle paler markings, often showing yellowish or cream-colored crescents or triangular spots on the dorsal abdomen, though these can be faint or absent in very dark older specimens.
Web Type
Builds an irregular, messy tangle web, commonly known as a cobweb, typically constructed in dark, undisturbed corners near ground level or high up in ceiling angles and wall junctions.
Eye Arrangement
Eight small eyes arranged in two slightly curved, parallel rows of four across the front of the cephalothorax, typical of the family Theridiidae.
Leg Characteristics
Long, slender legs with distinct reddish-brown to dark brown coloring. The legs lack prominent spines but have fine hairs and the characteristic comb structure on the hind tarsi.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom (latrotoxin-like components), but it is significantly milder than that of true widow spiders (Latrodectus).
Medical Significance
Minimally dangerous to humans. Bites are rare and usually occur only when the spider is trapped against the skin. Symptoms typically include localized pain, redness, and swelling, occasionally accompanied by mild systemic symptoms that resolve on their own.
Safety Recommendations
Wear gloves when cleaning dark, undisturbed spaces like woodpiles or basements. If relocation is necessary, gently guide the spider into a container using a piece of card.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution found worldwide in temperate regions. Commonly found indoors in dark corners of basements, garages, and sheds, and outdoors under rocks, bark, and ledges.
Behavior & Temperament
Timid and non-aggressive. It spends most of its time hanging upside down in its web. When disturbed, it typically retreats quickly, plays dead, or drops from the web rather than biting.
Diet & Prey
Feeds primarily on crawling and flying insects, woodlice, and occasionally other spiders trapped in its sticky cobweb.
Seasonal Activity
Active year-round indoors, with peak mating and visibility occurring during the warmer late summer and autumn months.
Description
Steatoda grossa, commonly known as the false black widow, is a frequent indoor companion that often startles homeowners due to its superficial resemblance to the medically significant black widow. With its glossy, rounded dark body and preference for quiet structural corners, it is a master pest controller silently managing household insect populations.
Key Features
Glossy, globular abdomen, lack of a red hourglass marking, dark purplish-brown coloration, and association with tangled cobwebs in structural corners.
Similar Species
Latrodectus species (True Black Widows), which feature the distinctive red hourglass marking on the ventral abdomen and lack the subtle pale dorsal markings often seen on Steatoda grossa.
Life Cycle
Females produce spherical, papery silk egg sacs containing up to several hundred eggs. Spiderlings disperse via ballooning or crawling. They undergo multiple molts over a lifespan of several years for females.
Ecological Importance
Acts as an effective natural pest control agent in and around human habitations, consuming flies, mosquitoes, roaches, and other household pests.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and frequently expanding alongside human development.
Interesting Facts
Despite the intimidating 'false widow' moniker, these spiders are quite docile and have been known to actively prey on true black widows when they encounter them.
Photography Tips
Use macro lenses with gentle diffused lighting to capture the glossy texture of the abdomen without causing the spider to retreat into shadow.
Identified: 2026-08-08T19:35:34.700092