False Black Widow, Cupboard Spider, Dark Comb-Footed Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Characterized by a comb of serrated bristles on the tarsus of the fourth leg used for throwing silk.
Physical Description
A medium-sized spider with a bulbous, globose abdomen and a smaller cephalothorax. The surface is smooth and glossy, lacking the dense hairs found on wolf spiders. Females are much larger and more robust than males, possessing a characteristic 'false widow' silhouette.
Size Estimate
The specimen appears to be an adult female with a body length of approximately 6-10mm and a total leg span of 20-25mm. Males are typically smaller (4-6mm) and more slender.
Coloration & Markings
Deep purplish-brown to near black base color. A pale, crescent-shaped band is often visible on the anterior portion of the abdomen. While this specimen appears dark, others may show faint chevrons or spots. Crucially, it lacks the bright red hourglass found on true black widows.
Web Type
Tangle web or cobweb. A messy, three-dimensional scaffold of sticky silk built in corners, under boxes, or in dark crevices. It lacks the geometric symmetry of an orb web.
Eye Arrangement
8 eyes in two rows of four. The eyes are small and typical of cobweb spiders, which rely more on web vibrations than vision for hunting.
Leg Characteristics
Relatively long, slender legs compared to the body. Dark brown or reddish-brown, often matching the cephalothorax. The legs are held in a typical 'crouched' stance when the spider is at rest on a surface.
Venom & Safety Information
Venom Information
Contains latrodectism-like toxins (alpha-latrotoxins) but in much lower concentrations than true widows. The venom is neurotoxic but usually only causes localized reactions in humans.
Medical Significance
Low to moderate medical significance. Bites are painful (similar to a wasp sting) and may cause localized swelling, malaise, or nausea. Symptoms usually resolve within 24-48 hours. Seek medical attention if a systemic allergic reaction occurs.
Safety Recommendations
Avoid sticking bare hands into dark, undisturbed corners or under stored items like the yellow bin pictured. To relocate, use the 'cup and card' method. Bites are rare and usually occur when a spider is trapped in clothing.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found worldwide. Highly synanthropic, preferring man-made structures like garages, basements, sheds, and cupboards. Occasionally found under rocks or bark in temperate climates.
Behavior & Temperament
Sedentary and nocturnal. They are generally timid and will retreat to a crevice if disturbed. They only bite if pressed against skin or handled roughly; they are not aggressive toward humans.
Diet & Prey
Generalist predators feeding on various crawling insects, including beetles, woodlice, and other spiders (including true black widows). They use sticky 'gumfoot' lines in their web to snag prey.
Seasonal Activity
Active year-round in indoor environments. Outdoors, peak activity and mating occur in late summer and autumn.
Description
The Steatoda grossa is a common inhabitant of human dwellings, often mistaken for the more dangerous Black Widow. With its glossy, dark, bulbous abdomen, it plays a vital role as a domestic pest controller, silently patrolling dark corners for unwanted insects.
Key Features
Glossy bulbous abdomen, dark chocolate/purple-black color, pale crescent on front of abdomen, lack of red hourglass, and construction of messy cobwebs.
Similar Species
Latrodectus species (Black Widows - distinguished by red hourglass), Steatoda nobilis (Noble False Widow - has a skull-like abdominal pattern), and Steatoda borealis.
Life Cycle
Females produce several off-white, papery, spherical egg sacs (visible in the photo). Each can contain 40-100 eggs. Lifespan for females can reach up to 6 years, while males live significantly shorter lives.
Ecological Importance
Highly beneficial for pest control; they consume significant numbers of ants, roaches, and woodlice that enter homes and outbuildings.
Conservation Status
Not evaluated by IUCN; however, they are widespread and abundant, often considered an invasive or introduced species in many parts of the world.
Interesting Facts
These spiders are known predators of the actual Black Widow. In some laboratory studies, they have been successfully used to track how venom evolved in the Theridiidae family.
Photography Tips
Focus on the dorsal (top) pattern of the abdomen and the junction between the segments. Using a flashlight from the side can help reveal the faint crescent markings or chevron patterns hidden by the dark glossy skin.
Identified: 2026-07-12T20:55:09.936481