False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Family Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded, bulbous abdomen, comb-like serrated setae on the hind tarsi used for flinging silk over prey, and typically building irregular, sticky tangle webs.
Physical Description
The spider has a compact, glossy appearance with a rounded, bulbous abdomen and a smaller, oval cephalothorax. The body texture is smooth and leathery rather than heavily haired. Sexual dimorphism is present, with females being notably larger, rounder, and bulkier than the smaller, more slender 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 approximately 20 to 30 mm. This specimen appears to be an adult.
Coloration & Markings
The base coloration ranges from deep brownish-purple to nearly black or dark charcoal. The dorsal abdomen displays distinct yellowish, cream, or pale orange triangular and crescent-shaped spots and pale lines, sometimes forming subtle chevron patterns.
Web Type
Builds an irregular, messy tangle web or cobweb constructed in dark, sheltered crevices, often close to ground level or in corners of indoor structures, utilizing sticky silk threads designed to snare crawling insects.
Eye Arrangement
Consists of eight small eyes arranged in two parallel, slightly curved horizontal rows of four each across the front of the cephalothorax, typical of the theridiid family.
Leg Characteristics
The legs are relatively long, slender, and unbanded, matching the dark brownish-black coloration of the body. They possess fine hairs and a specialized comb of serrated bristles on the hind tarsi for manipulating silk.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom (latrotoxin-like components), but it is significantly less potent than that of true widow spiders (Latrodectus spp.).
Medical Significance
Low medical significance. Bites are rare and usually occur only when the spider is trapped against human skin. Symptoms generally include mild local pain, redness, and swelling, occasionally accompanied by mild systemic symptoms that resolve without intervention.
Safety Recommendations
Avoid handling with bare hands; if relocating, use a container and a piece of card to guide the spider inside. Wear gloves when cleaning dark, undisturbed spaces where they may nest.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution found worldwide in temperate and tropical regions. Prefers dark, humid microhabitats such as outbuildings, cellars, under rocks, hollow logs, and dark corners indoors.
Behavior & Temperament
Non-aggressive and reclusive. They spend most of their time stationary in their webs. When disturbed, they typically retreat to a hide, drop from the web, or curl up defensively rather than attack.
Diet & Prey
Feeds primarily on crawling insects including roaches, woodlice, earwigs, and other spiders, occasionally capturing small vertebrates that blunder into their low-slung webs.
Seasonal Activity
Active year-round indoors, with peak outdoor visibility and mating activity occurring during the warmer summer and autumn months.
Description
Steatoda grossa, commonly known as the false black widow, is a frequent indoor and garden dweller easily mistaken for its more dangerous relatives due to its dark, bulbous physique. Distinguished by pale yellowish markings on its glossy dark abdomen, this reclusive cobweb spider quietly patrols dark corners, serving as an effective natural pest controller while posing minimal threat to humans.
Key Features
Glossy, dark brownish-purple globular abdomen featuring pale yellowish or cream spots, lack of a red hourglass marking, and association with an irregular, messy cobweb.
Similar Species
True Black Widow (Latrodectus mactans) is often confused with Steatoda grossa. True widows can be distinguished by the prominent red hourglass marking on the underside of the abdomen and a jet-black, velvety finish without pale dorsal spots.
Life Cycle
Females produce papery, brownish egg sacs containing dozens to hundreds of eggs, hanging them within the web retreat. Spiderlings hatch after a few weeks, disperse via ballooning or crawling, molt multiple times, and reach maturity within a year.
Ecological Importance
Acts as an important nocturnal predator controlling populations of household and garden arthropods, serving as a valuable component of local urban and rural food webs.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and frequently expanding due to human habitation and global transport.
Interesting Facts
False black widows can live for several years. Despite their intimidating appearance and shared family lineage with widow spiders, they help suppress household pest populations effectively and safely.
Photography Tips
Use macro lenses with a ring flash or diffused side lighting to highlight the glossy texture and yellow abdominal markings without casting harsh shadows. Photograph from above to capture the full dorsal pattern.
User Notes
Yellowish body spots
Identified: 2026-08-25T01:32:53.821722