False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded abdomen, comb-like setae on the fourth tarsus for pulling silk, and the construction of irregular tangle webs.
Physical Description
The spider has a bulbous, glossy, oval-shaped abdomen and a relatively compact cephalothorax. The texture is smooth and somewhat shiny, lacking heavy pubescence. Females are noticeably larger and rounder than males, which have slimmer abdomens.
Size Estimate
Body length ranges from 6 to 10.5 mm for females, while males are slightly smaller at 4 to 6 mm. Leg span is approximately 20 to 25 mm. This specimen appears to be an adult or sub-adult.
Coloration & Markings
Base coloration ranges from deep reddish-brown to dark purplish-black or charcoal. The abdomen features faint, pale yellowish or grayish chevron or crescent-shaped markings, though these can sometimes be indistinct or absent in very dark specimens.
Web Type
Constructs an irregular, sticky tangle web often referred to as a cobweb. These webs are typically built in dark, sheltered crevices near ground level, corners of rooms, or under furniture.
Eye Arrangement
Consists of eight small eyes arranged in two horizontal rows of four each, typical of the family Theridiidae, with lateral eyes often touching or closely grouped.
Leg Characteristics
Legs are moderately long and slender, featuring distinct dark banding or rings along the segments. They lack heavy spination but possess specialized comb-like structures on the hind tarsi for manipulating silk.
Venom & Safety Information
Venom Information
Contains neurotoxic components typical of theridiids (latrotoxin-like, though much milder). Envenomation is rare as they rarely bite unless heavily pressured against skin.
Medical Significance
Not medically significant. A bite may cause localized pain, redness, and swelling lasting a few hours, occasionally accompanied by mild systemic symptoms (Steatodism), but no lasting harm.
Safety Recommendations
Avoid direct handling with bare hands. If found inside, it can be easily relocated outside using a cup and a piece of paper. No professional pest control is typically necessary.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found worldwide in temperate and subtropical regions. Highly synanthropic, commonly inhabiting human dwellings, garages, sheds, under rocks, and in dark crevices around buildings.
Behavior & Temperament
Non-aggressive and timid, preferring to retreat or play dead when disturbed. They are strictly sedentary, spending most of their time stationary in their webs, and are primarily nocturnal hunters.
Diet & Prey
Feeds on a wide variety of crawling and flying insects, including cockroaches, woodlice, earwigs, and other spiders. Can successfully capture prey much larger than itself using sticky silk snares.
Seasonal Activity
Active year-round indoors, with peak visibility and wandering behavior for males searching for mates occurring during the late summer and autumn months.
Description
Steatoda grossa, widely known as the False Black Widow, is a common household spider often mistaken for its more dangerous relatives due to its dark, bulbous physique. Despite this, it is a harmless, beneficial pest controller that quietly tends to its messy cobweb in forgotten corners.
Key Features
Glossy, bulbous abdomen with pale chevron markings, dark reddish-brown to black coloration, lack of a red hourglass shape, and association with irregular tangle webs.
Similar Species
Latrodectus species (True Black Widows), which feature a distinct red hourglass marking on the ventral abdomen and lack pale chevrons; other Steatoda species which vary subtly in banding and coloration.
Life Cycle
Females produce spherical, brownish silk egg sacs containing up to 200 eggs, often hanging within the web. Spiderlings disperse via ballooning or crawling after hatching. Lifespan can be several years for females.
Ecological Importance
Acts as an effective natural pest control agent inside and around human habitations, helping to keep populations of household insect pests in check.
Conservation Status
Not evaluated by the IUCN, but secure and widely distributed globally as a successful introduced and native species.
Interesting Facts
False Black Widows are known to prey upon true black widows and other potentially dangerous spiders, making them surprisingly beneficial neighbors in regions where both occur.
Photography Tips
Use macro lenses with a high depth of field to capture the glossy texture and pale abdominal markings. Photograph from the side or slightly above while avoiding disturbing the web.
Identified: 2026-08-25T23:37:47.951516