False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded, bulbous abdomen, comb-like setae on the fourth tarsus used to pull silk over prey, and typically poor eyesight.
Physical Description
The spider features a robust, glossy body with a notably high, globular abdomen and a smaller, oval cephalothorax. The exoskeleton has a smooth, leathery appearance rather than being heavily hairy. Females are noticeably larger and rounder than males, which have slimmer abdomens and longer legs.
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 of roughly 20 to 30 mm. This specimen appears to be an adult female.
Coloration & Markings
Base coloration ranges from deep purple-brown to glossy black or dark charcoal. The dorsal abdomen often displays subtle lighter markings—such as pale yellowish or greyish chevrons, crescents, or triangular spots—though older specimens may appear entirely dark brown or black.
Web Type
Builds a tangled, irregular 3D cobweb often referred to as a tangle web. These webs are constructed in dark, sheltered areas like corners, crevices, under furniture, or along exterior foundations, featuring sticky vertical lines that snag crawling insects.
Eye Arrangement
Eight small, dark eyes arranged in two parallel, slightly curved rows of four (anterior and posterior lateral pairs touch or are closely spaced). The eyes are roughly equal in size and lack the dramatic enlargement seen in wolf or jumping spiders.
Leg Characteristics
Legs are moderately long, tapering, and relatively slender without heavy spination. They typically display faint reddish-brown or darker banding. The legs lack prominent claw tufts and are adapted for navigating their tangled webs rather than rapid running on open ground.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom (specifically latrotoxin-like compounds, though milder than true black widows). While a bite can cause localized pain, redness, and occasionally mild systemic symptoms like malaise or fever, it is generally not life-threatening to humans.
Medical Significance
Minimally dangerous to humans (steatodism). Bites are rare and usually occur only when the spider is trapped against human skin. Symptoms typically resolve within a few days. Basic first aid involves cleaning the wound and applying an ice pack; seek medical attention if an allergic reaction occurs.
Safety Recommendations
Avoid handling them bare-handed. If found indoors and desired to be removed, gently guide the spider into a cup using a piece of paper and release it outdoors. Standard work gloves protect against accidental bites during yard work.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found globally in temperate and subtropical regions. In North America, Europe, and parts of Australasia, they frequently inhabit human-made structures, basements, crawlspaces, garages, and exterior rock walls or fences.
Behavior & Temperament
Docile and non-aggressive. They spend most of their time stationary in their webs. When disturbed, they typically retreat, drop from the web on a silken thread, or curl up rather than bite.
Diet & Prey
Generalist predators feeding on crawling and flying insects, woodlice, and occasionally other spiders. Prey is subdued by wrapping it rapidly with sticky silk before delivering a paralyzing bite.
Seasonal Activity
Active year-round indoors, but most frequently encountered outdoors or migrating inside during late summer and autumn when males actively search for mates.
Description
The False Black Widow (Steatoda grossa) is a frequent companion to human dwellings, often found lingering in dark corners, under eaves, or against stone walls. Sporting a glossy, bulbous dark body and subtle pale markings, it is frequently mistaken for its dangerous relative, the black widow, though it lacks the iconic red hourglass. As a quiet, sedentary web-weaver, it plays a beneficial role in natural pest control without posing a significant threat to humans.
Key Features
Glossy, bulbous dark brown to black abdomen; lack of a red hourglass marking; presence of subtle pale chevron patterns on the back; association with irregular, messy cobwebs in sheltered corners.
Similar Species
True Black Widow (Latrodectus spp.) which features a distinct red hourglass or red spots on the underside of the abdomen and a jet-black finish. Steatoda grossa has lighter, more brownish tones and lacks bright red warning markings.
Life Cycle
Females produce several whitish or brownish silk egg sacs containing up to 200 eggs each, typically hidden within the web retreat. Spiderlings disperse via ballooning after hatching. They undergo multiple molts to reach maturity, with a lifespan generally ranging from 1 to several years for females.
Ecological Importance
Serves as an effective predator of insect populations around human habitations and natural rocky crevices, helping to regulate local invertebrate numbers while serving as prey for larger predators like birds and wasps.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and thriving globally, often expanding their range alongside human infrastructure.
Interesting Facts
Despite the frightening moniker 'false widow,' these spiders actively help homeowners by catching household pests like mosquitoes, flies, and occasional crawling invaders. They can survive long periods without food or water.
Photography Tips
Use macro lenses for close-up details of the abdomen pattern. Shoot from a side angle to capture the characteristic domed shape of the abdomen. Soft natural lighting or an external diffuser prevents harsh shadows on the glossy exoskeleton.
User Notes
On wall
Identified: 2026-08-15T09:35:33.395122