Cupboard Spider, False Black Widow, Dark Cobweb Spider
Steatoda grossa
Family 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 irregular tangle webs.
Physical Description
The spider has a robust, bulbous, egg-shaped abdomen and a relatively small cephalothorax. The body texture is smooth to slightly glossy with fine, inconspicuous hairs. It shows notable sexual dimorphism: females are significantly larger and rounder, while males are smaller, slimmer, and have longer legs.
Size Estimate
Body length ranges from 6 to 10.5 mm for females, and 4 to 6 mm for males. The total leg span can reach up to 20 to 30 mm, making it appear medium-sized in comparison to true black widows.
Coloration & Markings
Coloration ranges from dark purplish-brown to black, sometimes with a reddish-brown tinge. It may feature pale yellowish or greyish markings, often forming crescent shapes or faint chevron patterns on the dorsal abdomen, though mature specimens can appear entirely glossy black.
Web Type
Builds an irregular, messy tangle web often referred to as a cobweb, typically constructed in dark, protected crevices, under logs, or in structural voids.
Eye Arrangement
Features eight small eyes arranged in two horizontal rows of four, typical of the Theridiidae family, with lateral eyes often touching or closely grouped.
Leg Characteristics
Legs are relatively long and thin, lacking prominent spines but featuring fine hairs. They are uniformly dark brown or black, usually without distinct banding, and are held sprawling across the web or substrate.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom, but it is significantly less potent than that of true widow spiders (Latrodectus spp.).
Medical Significance
Minimally dangerous to humans. Bites are rare and usually occur only when the spider is trapped directly against the skin. Symptoms are generally mild, including local pain, redness, and swelling, occasionally accompanied by mild systemic effects like malaise, akin to a mild bee sting.
Safety Recommendations
Avoid handling spiders with bare hands, especially when moving heavy objects like logs. If found indoors, relocate the spider safely using a container and a piece of card. Standard first aid for a bite involves cleaning the wound and applying a cold pack.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, widely found in temperate regions worldwide including North America, Europe, and Australia. Prefers dark, humid microhabitats such as under thick logs, rocks, bark, and inside dark corners of human habitations, sheds, and basements.
Behavior & Temperament
Docile and non-aggressive. It relies on its web to detect vibrations from passing prey. When disturbed, it typically retreats to a hiding spot, curls into a defensive ball, or drops from the web rather than biting.
Diet & Prey
Feeds primarily on crawling insects, woodlice, and other spiders, including occasionally medically significant species. Prey is subdued by wrapping it in sticky silk and delivering a paralyzing bite.
Seasonal Activity
Active year-round in temperate indoor environments, with peak outdoor activity, mating, and wandering occurring during the warmer summer and autumn months.
Description
Steatoda grossa, commonly known as the false black widow, is a frequent dweller of dark recesses, both in natural woodland settings under thick logs and in human-made structures. Often mistaken for its more dangerous relative due to its glossy, dark, bulbous abdomen, this species is actually a beneficial and timid controller of household and garden pests.
Key Features
Glossy, bulbous, dark brown to black abdomen; absence of a bright red hourglass marking; irregular tangle web; smaller and less robust build compared to true black widows.
Similar Species
True Black Widows (Latrodectus spp.), which possess a distinct red hourglass marking on the underside of the abdomen and a more intensely jet-black coloration.
Life Cycle
Females construct tough, silken egg sacs containing up to several hundred eggs, which are hidden near the web. Spiderlings hatch and disperse via ballooning or crawling short distances. Lifespan for females can reach several years.
Ecological Importance
Serves as an effective predator of numerous insect populations, helping regulate pest species in both natural forest floors and domestic environments.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and often benefit from human-altered habitats.
Interesting Facts
Despite their common name 'false widow', they are known to occasionally prey upon true black widows that wander into their webs.
Photography Tips
Use macro photography lenses with good side-lighting to highlight the glossy texture of the abdomen without creating harsh glare. Ensure a safe distance and photograph against a neutral background to clearly display leg proportions and markings.
User Notes
Found under a 16” thick log
Identified: 2026-08-11T15:43:22.724951