Cupboard Spider, False Black Widow, Dark Cobweb Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a globose abdomen, comb-like serrated bristles on the tarsus of the fourth leg used to pull silk, and untidy tangled web structures.
Physical Description
The spider has a glossy, bulbous, egg-shaped abdomen and a compact, dark cephalothorax. The body surface is smooth and shiny rather than hairy. Females are noticeably larger and rounder, while males are slimmer with longer legs.
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 approximately 15 to 25 mm. This specimen appears to be an adult female.
Coloration & Markings
Deep brownish-purple to nearly black base coloration with subtle paler markings, often featuring creamy-yellowish triangular or crescent-shaped spots on the dorsal abdomen, though some individuals may be uniformly dark.
Web Type
Builds an irregular, messy tangle web (cobweb) in dark, secluded corners near the ground or along baseboards, consisting of sticky vertical catch threads connected to a retreat.
Eye Arrangement
Eight small eyes arranged in two slightly curved horizontal rows of four across the front of the cephalothorax, typical of the Theridiidae family.
Leg Characteristics
Legs are moderately long, slender, and glossy, matching the body's dark coloration, lacking prominent spines but featuring fine hairs and the characteristic comb-like structures on the hind tarsi.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom, but it is relatively mild compared to true widow spiders and generally not considered medically significant to healthy humans.
Medical Significance
Harmless to most humans. A bite may cause localized pain, redness, and mild swelling lasting a few hours, occasionally accompanied by minor systemic effects like malaise in sensitive individuals.
Safety Recommendations
Avoid handling with bare hands; use a jar and stiff paper to gently relocate individuals found indoors outside; wear gloves when cleaning dark, undisturbed spaces.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, highly adapted to living near and inside human habitations globally. Prefers dark, humid, undisturbed areas such as cellars, crawlspaces, garages, and behind furniture.
Behavior & Temperament
Timid and nocturnal, retreating when disturbed. They are not aggressive and will only bite if trapped directly against human skin.
Diet & Prey
Feeds primarily on crawling household insects including cockroaches, woodlice, earwigs, and other spiders, wrapping them securely with sticky silk before consuming.
Seasonal Activity
Active year-round indoors, with increased movement and mating activity typically occurring during late summer and autumn months.
Description
Steatoda grossa, commonly known as the false black widow, is a frequent indoor companion that often goes unnoticed due to its secretive habits. Recognized by its glossy, bulbous body and irregular cobweb, this spider serves as an efficient natural pest controller in homes and outbuildings.
Key Features
Glossy, globose abdomen; dark reddish-brown to black coloration with faint pale geometric markings; lack of a true red hourglass shape on the underside; messy cobweb construction.
Similar Species
Latrodectus species (True Widow Spiders), which possess a distinct red hourglass marking on the ventral abdomen and a matte rather than glossy finish; and other Steatoda species which vary slightly in size and pattern.
Life Cycle
Females produce several brownish silk egg sacs containing up to 200 eggs each. Spiderlings disperse via ballooning or crawling after hatching, maturing over several months through multiple molts, with a total lifespan of several years.
Ecological Importance
Acts as an important urban predator, helping to regulate and suppress populations of household pest insects without chemical intervention.
Conservation Status
Not evaluated by the IUCN, but secure and globally widespread due to successful human commensalism.
Interesting Facts
False black widows are known to prey upon true black widows and other potentially dangerous spiders, effectively reducing populations of more venomous species around homes.
Photography Tips
Use macro photography with a soft diffuser or ring light to highlight the glossy texture and subtle dorsal patterns without casting harsh shadows; maintain a safe macro distance.
Identified: 2026-08-01T15:19:04.811504