False Black Widow, Cupboard Spider, Dark Comb-Footed Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Family members typically feature a rounded, bulbous abdomen, comb-like bristles on the hind legs (tarsus IV), and construct irregular, tangled cobwebs.
Physical Description
The spider exhibits a bulbous, dark oval-to-spherical abdomen with a relatively small, glossy cephalothorax. The body surface appears smooth and slightly shiny with short, fine setae. Sexual dimorphism is strong in this species; females have larger, rounder abdomens while males are slimmer with longer legs.
Size Estimate
Body length is approximately 6 to 10 mm, with a leg span of around 15 to 25 mm. The specimen appears to be an adult or sub-adult female, fitting comfortably within the palm-scale context seen through the glass jar bottom.
Coloration & Markings
Dark reddish-brown to deep brownish-black overall. While true black widows have bright red hourglass markings on the underside, Steatoda grossa lacks red markings. Young specimens or lighter adults often feature pale crescent-shaped markings on the anterior abdomen and faint chevron spots down the dorsal center, though mature individuals can become almost uniformly dark.
Web Type
Constructs an irregular, sticky, three-dimensional tangle web or cobweb. The webs are usually built in dark, sheltered microhabitats such as crawlspaces, cupboards, basements, wall voids, and under debris.
Eye Arrangement
Has eight small eyes arranged in two transverse rows of four across the front of the carapace. The anterior median eyes are slightly elevated, typical of Theridiid comb-footed spiders.
Leg Characteristics
Legs are moderately long, slender, and tapered. Coloration matches the dark brown to blackish body. Leg IV features a distinct row of comb-like serrated bristles (tarsal comb) used to wrap prey in silk.
Venom & Safety Information
Venom Information
Contains mild neurotoxic venom (alpha-latrotoxin analogs), but significantly weaker than that of true black widows (Latrodectus species). Biting rarely occurs unless squeezed or pressed directly against skin.
Medical Significance
Not medically significant. Bites cause mild localized pain, minor swelling, and localized redness lasting a few hours to a day (steatodism). Systemic symptoms like mild sweating or nausea are exceedingly rare. Wash with soap and water; apply a cold pack if bitten.
Safety Recommendations
Harmless to humans and pets. If captured indoors, release outside into a shed, garden, or woodpile using the jar-and-cardboard method. Wear gloves when cleaning out dark storage areas or woodpiles to avoid accidental pinches.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution; native to Europe but now widespread across North America, Australasia, and parts of South America. Commonly synanthropic, thriving indoors, in sheds, basements, garages, and around building foundations.
Behavior & Temperament
Very timid, nocturnal, and non-aggressive. Prefers to stay hidden within its web or retreat during the day. When disturbed or threatened, it usually drops to the ground, curls into a tight ball, or retreats rather than bite.
Diet & Prey
Generalist predator feeding on crawling and flying insects such as ants, beetles, pillbugs, moths, and occasionally other spiders (including true black widows). Uses comb-feet to wrap silk around prey before delivering a venomous bite.
Seasonal Activity
Active year-round indoors due to climate-controlled human environments. Outdoors, peak activity occurs from late spring through autumn, with mating taking place in spring and early summer.
Description
Steatoda grossa, commonly known as the False Black Widow, is a widespread cobweb spider frequently found in human habitations. Often mistaken for dangerous black widows due to its dark body and bulbous abdomen, it completely lacks red hourglass markings and poses no major threat to humans. It serves as an effective natural pest controller indoors and around home foundations.
Key Features
Bulbous dark brown to black abdomen; total absence of bright red abdominal markings; comb-like bristles on tarsus IV; irregular tangle web construction; glossy dark carapace.
Similar Species
Latrodectus mactans (Southern Black Widow) and Latrodectus hesperus (Western Black Widow), which possess bright red hourglass patterns on the ventral abdomen; Steatoda nobilis (Noble False Widow), which features a cream-colored 'skull' or 'pentagon' abdominal pattern; Steatoda triangulosa (Triangulate Cobweb Spider), which has distinctive zig-zag/triangular dorsal patterns.
Life Cycle
Females produce spherical to teardrop-shaped white/off-white silken egg sacs containing 40 to 100+ eggs. Spiderlings emerge and disperse via ballooning or crawling. Females can live up to 5 years, while males typically live 1 to 1.5 years.
Ecological Importance
Acts as an effective urban biological control agent against indoor insect pests, including cockroaches, ants, woodlice, and pest beetles.
Conservation Status
Not evaluated by the IUCN; widespread, highly adaptable, and abundant globally with stable populations.
Interesting Facts
Despite being called a 'false widow', S. grossa is known to actively hunt and prey upon true black widow spiders in regions where their ranges overlap, sometimes helping control true widow populations around homes.
Photography Tips
Photograph from above to capture dorsal abdominal patterns and carapace shape. Use diffuse top-down lighting to minimize glares and reflections on glass jars or glossy exoskeletons.
Identified: 2026-07-25T14:27:17.451462