False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a globose abdomen, comb-like setae on the fourth tarsus used to pull silk over prey, and building irregular tangle webs.
Physical Description
The spider features a bulbous, globose abdomen and a smaller, oval cephalothorax. The overall appearance is glossy and smooth rather than densely hairy. Females are noticeably larger and rounder than males, which have slimmer abdomens and longer relative legs.
Size Estimate
Body length ranges from 6 to 10.5 mm for females, while males are slightly smaller at 4 to 6 mm. Total leg span is approximately 20 to 30 mm.
Coloration & Markings
Base coloration ranges from deep purple-brown to nearly black or dark charcoal. Some specimens display subtle lighter pale yellowish or reddish-brown markings, streaks, or chevron patterns on the dorsal abdomen, though these can be faint or absent in very dark individuals.
Web Type
Constructs an irregular, messy tangle web often referred to as a cobweb. These webs are typically built in dark, sheltered locations near ground level or in corners, featuring sticky vertical silk threads designed to trap walking insects.
Eye Arrangement
Has eight small eyes arranged in two distinct rows of four, typical of the Theridiidae family, consisting of lateral pairs that are closely touching and median eyes set on a slight tubercle.
Leg Characteristics
Legs are relatively long, thin, and taper smoothly without prominent spines. They are generally uniform dark brown or black matching the body, lacking distinctive banding, and feature specialized comb-like structures on the hind tarsi.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom designed primarily for invertebrate prey. While a bite can cause localized pain, blistering, and mild systemic symptoms in humans, it is generally not life-threatening.
Medical Significance
Minor medical significance. Bites are rare and usually occur only when the spider is trapped directly against human skin. Symptoms can mimic a mild form of steatodism, resembling a localized bee sting with some discomfort, but serious systemic complications are extremely rare.
Safety Recommendations
Avoid direct handling with bare hands. Wear gloves when cleaning out dark, undisturbed areas like woodpiles or basements. If found indoors, the spider can be safely relocated outdoors using a container and a piece of card.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution across temperate and subtropical regions worldwide. Frequently found around human habitations, in dark corners of basements, garages, outbuildings, under logs, and within woodpiles or rock crevices.
Behavior & Temperament
Timid, sluggish, and nocturnal by nature. They spend most of their time hanging upside down in their webs. They are non-aggressive and will typically curl into a ball or drop to the ground when disturbed rather than bite.
Diet & Prey
Feeds primarily on crawling and flying insects including roaches, woodlice, earwigs, flies, and occasionally other spiders. Prey is subdued using sticky silk and potent venom before being hauled up into the retreat.
Seasonal Activity
Active year-round indoors, though sightings and wandering behavior peak during late summer and autumn when mature males actively search for females to mate.
Description
Steatoda grossa, commonly known as the False Black Widow, is a frequent household guest that often causes unwarranted alarm due to its superficial resemblance to true black widows. Sporting a glossy, bulbous dark body, this spider prefers the quiet, undisturbed corners of human dwellings and outbuildings. As an adept cobweb weaver, it quietly patrols its sticky maze, acting as a natural pest control agent against crawling insects.
Key Features
Glossy, bulbous dark brown to purplish-black abdomen; absence of the bright red hourglass marking found on Latrodectus species; irregular tangle web structure; and theridiid comb-feet.
Similar Species
True Black Widow (Latrodectus species), which can be distinguished by the prominent red or orange hourglass on the ventral abdomen and a jet-black, satin-like finish. Other Steatoda species like Steatoda triangulosa feature distinct geometric patterns.
Life Cycle
Females construct tough, paper-like silk egg sacs containing up to several hundred eggs, typically hidden within their web retreat. Spiderlings hatch after a few weeks, disperse via ballooning or crawling, and undergo multiple molts over a multi-year lifespan.
Ecological Importance
Serves as an effective predator of household pests and agricultural insects, helping to naturally regulate populations of cockroaches, beetles, and flies within its local environment.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and often thriving in urbanized environments globally due to human co-habitation.
Interesting Facts
Despite the frightening moniker 'False Black Widow,' these spiders are exceptionally docile and their venom, while potent to insects, poses minimal risk to humans. They are capable of living for several years in favorable indoor conditions.
Photography Tips
Use macro lenses with good side-lighting to capture the glossy texture of the cephalothorax and abdomen. Photograph from a lateral or dorsal angle to highlight any subtle abdominal markings without disturbing the spider.
Identified: 2026-09-30T15:48:09.429544