Cupboard Spider, False Black Widow, Dark Cobweb Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae
Physical Description
The body is robust and bulbous, typical of cobweb spiders, featuring a shiny, globular abdomen that overhangs a smaller cephalothorax. The exoskeleton is smooth, leathery, and dark. Females are noticeably larger and rounder than the slender, smaller males.
Size Estimate
Body length ranges from 6 to 10.5 mm for females and 4 to 6 mm for males, with a leg span reaching up to 20 to 30 mm, representing a mature adult specimen.
Coloration & Markings
Deep purplish-brown, dark brown, or nearly black base coloration, often accented with pale yellowish, cream, or whitish triangular and crescent markings along the dorsal and lateral sides of the abdomen. The legs are unbanded or faintly banded in lighter brown tones.
Web Type
An irregular, sticky tangle web (cobweb) constructed in dark, sheltered crevices, corners, or cavities near ground level or inside structures.
Eye Arrangement
Eight small eyes arranged in two rows of four across the front of the carapace, typical of the Theridiidae family, with lateral eyes positioned close together.
Leg Characteristics
Long and slender legs lacking prominent spines, featuring distinct comb-like serrated bristles on the tarsus of the fourth pair of legs used for pulling silk from the spinnerets.
Venom & Safety Information
Venom Information
Neurotoxic venom that is not medically significant to humans, though a bite can cause localized pain, mild swelling, and occasional malaise.
Medical Significance
Low medical significance. While sometimes confused with true black widows due to the common name and globular shape, their bites are mild, non-lethal, and typically resolve on their own without severe systemic effects.
Safety Recommendations
Avoid handling with bare hands to prevent accidental bites. Relocate indoors spiders using a glass and a piece of card. Wear gloves when cleaning out dark, undisturbed storage areas.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution found worldwide in temperate regions. Prefers dark, humid microhabitats such as basements, crawlspaces, under bark, inside hollow logs, and around dark corners of human habitations.
Behavior & Temperament
Non-aggressive and reclusive. They spend most of their time hanging motionless upside down in their web, retreating rapidly when disturbed.
Diet & Prey
Generalist predator feeding on crawling insects, woodlice, and other spiders including potentially dangerous species like black widows. Prey is subdued using sticky silk and fast-acting venom.
Seasonal Activity
Active year-round indoors, but most commonly encountered and visible during late summer and autumn when mature males wander in search of mates.
Description
Steatoda grossa, commonly known as the cupboard spider or false black widow, is a frequent household guest that builds its messy, tangled webs in neglected corners. With its glossy, bulbous abdomen and rich dark coloration, it closely resembles its more dangerous relatives in the Latrodectus genus, leading to frequent misidentifications. Despite this superficial resemblance, this spider is timid, ecologically beneficial, and acts as a natural pest controller in homes and gardens.
Key Features
Glossy, globular dark brown to purple abdomen, absence of a red hourglass marking, presence of pale cream-colored markings, and creation of an irregular cobweb.
Similar Species
Latrodectus species (True Black Widows), which feature distinctive red markings such as an hourglass on the ventral abdomen; other Steatoda species like Steatoda triangulosa.
Life Cycle
Females produce papery, brownish egg sacs containing dozens to hundreds of eggs. Spiderlings hatch after a few weeks, disperse via ballooning or crawling, and molt multiple times to reach maturity, living for several years.
Ecological Importance
Acts as an effective biological control agent by consuming household pests, nuisance insects, and other arachnids, maintaining balanced local invertebrate populations.
Conservation Status
Not evaluated by the IUCN, but highly secure and widespread globally due to successful adaptation to human-modified environments.
Interesting Facts
Despite being called a false black widow, Steatoda grossa is actually known to occasionally prey upon true black widows by expertly subduing them with sticky silk in their own webs.
Photography Tips
Use macro lenses with a ring flash or diffused external lighting to capture the subtle pale markings and glossy skin texture without causing the spider to retreat into a dark crevice.
Identified: 2026-08-22T19:52:07.413741