False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Family Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded abdomen, comb-like serrated bristles on the tarsus of the fourth pair of legs used for flinging silk over prey, and typically building irregular three-dimensional tangle webs.
Physical Description
The spider has a bulbous, glossy, teardrop-to-oval shaped abdomen that hangs somewhat over the cephalothorax. The body is relatively robust with long, slender legs. The texture appears smooth and shiny, lacking dense hairs. There is noticeable sexual dimorphism, with females being significantly larger and more rotund 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 20 to 30 mm. This appears to be an adult female specimen based on the large, bulbous abdomen.
Coloration & Markings
Deep, rich dark coloration ranging from dark brown to purplish-black or glossy charcoal. Unlike true black widows, it lacks a red hourglass marking. Instead, it may feature faint, pale yellowish or grayish chevron or crescent markings on the dorsal side of the abdomen, though these can be very subtle or completely absent in fully melanistic dark adults.
Web Type
Builds an irregular, messy tangle web often referred to as a cobweb. The web consists of sticky silk threads crisscrossing in various directions, typically constructed in dark, undisturbed corners, near baseboards, inside structural crevices, or around windows and door frames.
Eye Arrangement
Has eight small eyes arranged in two horizontal rows of four each (anterior and posterior lateral eyes grouped together, with median eyes separated), typical of the family Theridiidae.
Leg Characteristics
Legs are long, slender, and uniformly dark brown to reddish-brown, generally matching the cephalothorax. They lack prominent spination but feature fine hairs and the characteristic comb-like serrae on the hind legs for silk manipulation. They rest in a typical sprawling posture within the web.
Venom & Safety Information
Venom Information
Contains neurotoxic components (alpha-latrotoxin-like proteins, though less potent than true widows). Envenomation causes localized pain, mild swelling, and sometimes systemic symptoms collectively known as steatodism, which is much milder than latrodectism.
Medical Significance
Medically significant in rare cases, but generally considered mildly venomous. A bite can cause moderate local pain lasting a few hours, blistering at the site, headache, and fatigue, but severe systemic effects are uncommon and rarely require more than symptomatic treatment.
Safety Recommendations
Avoid handling bare-handed when cleaning dark corners or basements. If found inside, it can be safely relocated outdoors using a container 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 worldwide in temperate and subtropical regions, frequently associated with human habitations. Prefers dark, dry, sheltered microhabitats such as basements, crawlspaces, under furniture, inside hollow blocks, garages, and outdoor sheds.
Behavior & Temperament
Reclusive, nocturnal, and non-aggressive. They spend most of their time hanging upside down in their webs. When disturbed, they typically retreat to a nearby crevice or drop out of the web, only biting if directly pressed or trapped against human skin.
Diet & Prey
Feeds primarily on crawling and flying insects, including woodlice, flies, cockroaches, earwigs, and other spiders. Uses its sticky cobweb to entangle prey before wrapping it securely and delivering a paralyzing venom bite.
Seasonal Activity
Active year-round indoors, but mating and wandering behavior peaks during late summer and autumn when adult males actively search for female webs.
Description
Steatoda grossa, commonly known as the false black widow, is frequently mistaken for its dangerous relative due to its dark, glossy, bulbous appearance. As an expert home-dweller, it quietly spins its sticky cobwebs in forgotten corners, serving as a silent predator that keeps household insect populations in check. Despite its intimidating silhouette, it is a timid creature that prefers retreat to confrontation.
Key Features
Glossy, dark purple-brown to black bulbous abdomen, lack of a red hourglass marking, presence of faint pale chevrons or spots on the abdomen, and construction of messy indoor cobwebs.
Similar Species
Latrodectus species (True Black Widows), which feature the distinct bright red hourglass marking on the underside of the abdomen. Steatoda nobilis (Noble False Widow), which features more distinct skull- or crescent-shaped pale markings.
Life Cycle
Females produce several whitish or brownish silk egg sacs containing up to 200 eggs each. Spiderlings hatch within a few weeks, disperse via ballooning or crawling, and undergo multiple molts over a lifespan of up to several years for females.
Ecological Importance
Acts as an effective natural pest control agent inside and around human structures by capturing and consuming nuisance insects such as flies, roaches, and beetles.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and frequently expanding globally due to human commerce and global trade.
Interesting Facts
False black widows are known to successfully prey on much larger animals, including venomous spiders like brown recluses and even small vertebrates, by using their exceptionally strong silk and sticky web lines.
Photography Tips
Use macro lenses with a ring flash or diffuser to capture the glossy texture of the abdomen without harsh reflections. Photograph from the side and dorsal view to clearly document the lack of red markings and any faint patterns.
Identified: 2026-08-10T07:44:28.610566