Cupboard Spider, False Black Widow, Dark Cobweb Spider
Steatoda grossa
Family Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a globular abdomen, comb-like setae on the fourth tarsus used for flinging silk over prey, and typically building irregular tangle webs.
Physical Description
The spider has a bulbous, oval-shaped abdomen and a relatively compact, glossy cephalothorax. The body appears smooth with fine, sparse hairs. There is subtle sexual dimorphism, with females being notably larger, rounder, and heavier-bodied, while males are smaller, slenderer, and possess longer legs relative to their body size.
Size Estimate
Body length ranges from roughly 6 to 10.5 mm for females, and slightly smaller for males (around 4 to 7 mm). The leg span is approximately 15 to 25 mm. This specimen appears to be an adult or subadult based on the well-developed proportions and distinct abdominal markings.
Coloration & Markings
The base coloration ranges from deep brownish-purple to dark brown or nearly black. The dorsal abdomen features distinct pale yellowish or cream-colored geometric markings, often forming chevron or crescent patterns. The legs are typically yellowish-brown with darker banding at the joints.
Web Type
Builds an irregular, sticky tangle web commonly referred to as a cobweb. These webs are constructed in dark, sheltered, undisturbed locations such as corners of rooms, crevices, beneath furniture, inside cupboards, or around hollow logs and stone walls.
Eye Arrangement
Consists of eight small eyes arranged in two horizontal rows of four each, typical of the Theridiidae family. The eyes are generally uniform in size, clustered on the anterior portion of the cephalothorax.
Leg Characteristics
Legs are moderately long and slender, featuring distinct dark banding or rings. They lack heavy spination but possess specialized comb-like structures (comb-feet) on the hind tarsi used to manipulate silk during prey capture. The resting posture typically involves clinging upside down within the tangle web.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom designed to subdue insect prey. While it can bite humans if firmly pressed against the skin, the venom is not medically significant and rarely causes systemic effects.
Medical Significance
Low medical significance. Bites are uncommon and usually occur only when trapped against clothing or skin. Symptoms are generally localized, including mild pain, redness, and slight swelling that resolves within a day. No systemic envenomation syndrome is associated with this species.
Safety Recommendations
Avoid handling bare-handed. If found inside a home, gently relocate the spider outdoors using a cup and a piece of paper. Standard house cleaning and sealing cracks help prevent unwanted indoor populations.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found worldwide in temperate and subtropical regions. Highly synanthropic, frequently inhabiting human dwellings, outbuildings, garages, and basements, as well as natural habitats under bark, rocks, and hollow tree trunks.
Behavior & Temperament
Docile and non-aggressive. They are nocturnal hunters that spend most of their time stationary in their webs. When disturbed, they typically retreat quickly into a crevice or drop from the web, playing dead rather than attacking.
Diet & Prey
Feeds primarily on crawling insects, woodlice, and other spiders including potentially dangerous species like true black widows. Prey is subdued by wrapping it rapidly in sticky silk before delivering a paralyzing bite.
Seasonal Activity
Active year-round indoors, though sightings peak during late summer and autumn when adult males actively wander in search of mates.
Description
Steatoda grossa, commonly known as the cupboard spider or false black widow, is a frequent indoor companion that often goes unnoticed in dark corners and neglected spaces. With its glossy, bulbous abdomen and pale geometric markings, it bears a superficial resemblance to true widow spiders but lacks the dangerous potency. As a skilled web-weaver, it quietly manages household insect populations while remaining remarkably reclusive and docile.
Key Features
Glossy, bulbous dark brown to purplish abdomen with pale cream-colored chevron or crescent markings; lack of a red hourglass shape; presence of irregular cobwebs in dark, sheltered indoor or outdoor microhabitats.
Similar Species
True Black Widow (Latrodectus spp.), which features a shinier jet-black body often marked with a distinct red hourglass underneath. Steatoda grossa can be distinguished by its brownish-purple hue and pale dorsal markings.
Life Cycle
Females produce pear-shaped silk egg sacs containing dozens to hundreds of eggs, typically hidden within their webs or nearby retreats. Spiderlings disperse shortly after hatching. Molting occurs multiple times throughout growth, and adults can live for several years under favorable conditions.
Ecological Importance
Acts as an effective natural pest controller in domestic and wild ecosystems, suppressing populations of crawling insects, woodlice, and other arthropods.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and heavily adapted to human environments.
Interesting Facts
Despite being called a false black widow, Steatoda grossa is known to occasionally prey upon true black widows by invading their webs, wrapping them in heavy silk, and consuming them.
Photography Tips
Photograph from a side or top-down angle using macro settings to capture the intricate pale markings on the abdomen. Ensure adequate soft lighting to reveal the subtle purple-brown sheen without creating harsh reflections.
Identified: 2026-10-11T20:01:52.055915