Cupboard Spider, False Black Widow, Dark Cobweb Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a globose abdomen, comb-like serrated bristles on the fourth tarsus used to pull silk over prey, and irregular, three-dimensional tangle webs.
Physical Description
The spider features a robust, bulbous, egg-shaped abdomen and a smaller, oval cephalothorax. The body texture is smooth with fine, scattered hairs. Sexual dimorphism is present; females are significantly larger, rounder, and bulkier, while males are smaller, slender, and have proportionally longer legs.
Size Estimate
Body length typically ranges from 6 to 10.5 mm for females and 4 to 6 mm for males, with a leg span up to 25 to 35 mm. This specimen appears to be an adult female based on the prominent, rounded abdominal profile.
Coloration & Markings
Base coloration ranges from deep purplish-brown to charcoal black, occasionally with a dark reddish-brown hue. The dorsal abdomen may feature subtle, pale yellowish or grayish markings, sometimes forming faint chevron patterns or crescents, though older specimens often appear entirely dark and glossy.
Web Type
Builds an irregular, messy tangle web, commonly known as a cobweb. These webs are constructed in dark, sheltered crevices, corners, under furniture, or high up on walls and ceilings, consisting of sticky vertical catch threads connected to a central retreat.
Eye Arrangement
Has eight small eyes arranged in two parallel rows of four across the front of the cephalothorax, typical of the Theridiidae family, with lateral eyes often touching or closely paired.
Leg Characteristics
Legs are moderately long, slender, and taper toward the ends, featuring subtle dark banding or rings on lighter joints. They lack heavy spination but possess the characteristic comb-like serrated setae on the hind tarsi used for wrapping prey.
Venom & Safety Information
Venom Information
Possesses a neurotoxic venom (latrotoxin-like compounds, though much milder than true black widows). It is not life-threatening to humans, but envenomation can cause localized pain, redness, and occasional mild systemic symptoms like malaise.
Medical Significance
Minimally medically significant. A bite can cause painful localized swelling and minor symptoms similar to a wasp sting, but severe systemic effects are rare. First aid involves washing the area and applying ice; medical attention should be sought only if an allergic reaction occurs.
Safety Recommendations
Avoid handling with bare hands. If found in a living area, gently relocate the spider using a cup and a piece of cardstock. Keep corners clean to discourage web building.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution across temperate and subtropical regions worldwide, frequently associated with human habitations. Found indoors in dark corners, basements, and garages, and outdoors under rocks, loose bark, and within hollow logs.
Behavior & Temperament
Crepuscular and nocturnal, spending daylight hours hidden within its web retreat. They are generally timid, non-aggressive spiders that retreat when disturbed and only bite if trapped directly against human skin.
Diet & Prey
Feeds primarily on crawling insects, woodlice, and other spiders, including potentially dangerous species like black widows. Prey is intercepted in the sticky tangle web, quickly subdued with silk, and bitten.
Seasonal Activity
Active year-round indoors, with heightened mobility and visibility during late summer and autumn when mature males wander in search of females during the mating season.
Description
Steatoda grossa, widely known as the False Black Widow, is a frequent indoor roommate that often goes unnoticed in the quiet corners of homes and garages. With its shiny, bulbous, dark body and preference for out-of-the-way cobwebs, it serves as a stealthy and efficient controller of household insect populations. Though its resemblance to the true black widow often causes unnecessary alarm, it is a largely harmless and beneficial neighbor.
Key Features
Glossy, globose, dark purple-brown to black abdomen; absence of a bright red hourglass marking; irregular tangle web construction; typically found high up in indoor corners.
Similar Species
True Black Widow (Latrodectus species), which features a distinctive red or orange hourglass marking on the ventral abdomen and a shinier pitch-black body. Steatoda grossa lacks bright red ventral markings.
Life Cycle
Females produce tough, brownish silk egg sacs containing up to 200 eggs, attaching them near the web. Spiderlings hatch and disperse via ballooning or crawling. Adults can live for several years, with females outliving males significantly.
Ecological Importance
Acts as an effective natural pest controller in domestic and semi-natural environments by regulating populations of crawling insects and suppressing other spider species.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and frequently expanding alongside human urbanization.
Interesting Facts
Despite their common name, false black widows actively prey on true black widows in regions where their habitats overlap, successfully subduing them using superior silk-wrapping techniques.
Photography Tips
Use macro lenses with good side-lighting to capture the subtle pale markings and glossy texture of the abdomen without using harsh, direct flash that causes unwanted glare.
Identified: 2026-08-30T13:31:31.069987