False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded, bulbous abdomen, comb-like setae on the fourth tarsus used for flinging silk over prey, and irregular tangle webs.
Physical Description
The spider has a compact, glossy appearance with a distinctively large, spherical to bulbous abdomen that overhangs a smaller cephalothorax. The body texture is smooth and shiny, lacking dense hairs. This specimen is an adult female, showing pronounced bodily volume typical of mature females ready to produce egg sacs.
Size Estimate
Body length ranges from 6 to 10.5 mm for females, with a total leg span reaching approximately 20 to 25 mm. This specimen is an adult female of medium-to-large size for the species.
Coloration & Markings
Deep, rich brownish-purple to dark purplish-black base coloration with a glossy sheen. Unlike true widows, it completely lacks red markings or a ventral hourglass. Faint, pale yellowish or grayish chevron or crescent markings may sometimes be visible on the dorsal abdomen, though this individual appears predominantly dark and uniform.
Web Type
Constructs an irregular, messy tangle web often referred to as a cobweb. These webs are typically built in dark, sheltered areas close to the ground, inside outbuildings, basements, or hollow spaces.
Eye Arrangement
Eight small eyes arranged in two horizontal rows of four across the front of the cephalothorax, typical of the theridiid family, with lateral eyes often touching or closely juxtaposed.
Leg Characteristics
Legs are moderately slender, relatively long, and taper toward the ends. They are colored similarly to the body, ranging from dark brown to reddish-brown, and may show faint darker banding. They feature small spines but lack the heavy spination found in hunting spiders.
Venom & Safety Information
Venom Information
Possesses a neurotoxic venom containing latrotoxin-like components, though significantly weaker than that of true widow spiders (Latrodectus species).
Medical Significance
Minimally medically significant. A bite can cause mild local pain, redness, and swelling, occasionally accompanied by mild systemic symptoms like malaise or headache, but severe envenomation (steatodism) is rare and self-limiting.
Safety Recommendations
Avoid handling barehanded. If found inside, gently relocate outdoors using a cup and a piece of card. If bitten, clean the area with soap and water and apply a cold compress.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found globally in temperate and subtropical regions including North America, Europe, and parts of Australia. Prefers dark, humid, undisturbed microhabitats such as woodpiles, basements, crawlspaces, under rocks, and inside neglected sheds.
Behavior & Temperament
Reclusive, nocturnal, and non-aggressive. It spends most of its time hanging upside down in its web. When disturbed, it will typically drop to the ground and play dead or retreat rapidly into a crevice rather than bite.
Diet & Prey
Feeds primarily on crawling insects, woodlice, and occasionally other spiders. It uses sticky silk threads in its cobweb to trap wandering arthropods before subduing them with venom.
Seasonal Activity
Active year-round indoors, but most commonly noticed in late summer and autumn during peak mating season when wandering males search for females.
Description
The False Black Widow (Steatoda grossa) is frequently mistaken for its dangerous relative, the Black Widow, due to its dark, bulbous physique and glossy dark coloration. However, this harmless web-dweller is a beneficial household tenant that helps control pest populations. Thriving in dark corners and crevices, it patiently waits in its tangled web for unsuspecting prey.
Key Features
Glossy bulbous abdomen, dark brownish-purple coloration, absence of red markings or an hourglass shape, and association with an irregular tangle web.
Similar Species
True Black Widow (Latrodectus mactans) and other Steatoda species. Distinguished from true widows by the lack of bright red or orange underside markings, and from other false widows by its larger size and deep purplish-brown hue.
Life Cycle
Females construct tough, brownish silk egg sacs containing up to 200 eggs, hidden near the web. Spiderlings hatch after several weeks and disperse via ballooning. Molting occurs multiple times before reaching maturity, with a potential lifespan of several years for females.
Ecological Importance
Acts as an effective natural predator for household and garden pests, keeping populations of crawling insects in check and playing a steady role in local food webs.
Conservation Status
Not evaluated by the IUCN, but populations are widespread, stable, and thriving globally, often expanding alongside human habitations.
Interesting Facts
Despite their ominous name, False Black Widows are cowardly and prefer retreat over confrontation. Their venom, while capable of causing mild discomfort in humans, has been studied for its fascinating biochemical parallels to true widow toxins.
Photography Tips
Use macro lenses with a diffuser to capture the glossy texture of the abdomen without harsh reflections. Photograph from the side and top to clearly document the lack of red markings.
Identified: 2026-10-02T00:57:45.895071