False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a generally globose abdomen, small size, and a distinct comb of serrated bristles on the tarsus of the fourth pair of legs used to pull silk from the spinnerets.
Physical Description
The spider has a bulbous, globose, glossy abdomen and a much smaller, darker cephalothorax. The legs are relatively thin and taper outward. Females are larger with heavily rounded abdomens, while males are slimmer and more elongated.
Size Estimate
Body length ranges typically from 6 to 10.5 mm for females and 4 to 6 mm for males, with a leg span up to around 20 to 25 mm. This specimen appears to be an adult female.
Coloration & Markings
Deep purplish-brown to glossy black overall, sometimes featuring subtle pale yellowish or cream markings or faint chevrons on the dorsal abdomen, though these can be very dark and hard to see against the shiny surface.
Web Type
Tangle web or irregular cobweb constructed in dark, undisturbed areas such as corners of rooms, under furniture, in sheds, or near ground level outdoors.
Eye Arrangement
Eight small eyes arranged in two rows of four, typical of the family Theridiidae, with lateral eyes often touching or closely juxtaposed.
Leg Characteristics
Legs are moderately long and slender, typically dark brown or reddish-brown, lacking heavy spines but equipped with a comb of serrated setae on the fourth tarsus characteristic of cobweb spiders.
Venom & Safety Information
Venom Information
Neurotoxic venom, but significantly milder than that of true widow spiders (Latrodectus). Envenomation in humans is uncommon and usually results in mild local pain and swelling.
Medical Significance
Not medically significant. Bites may cause localized pain, redness, and occasionally mild systemic symptoms like malaise or headache, but these typically resolve without medical intervention.
Safety Recommendations
Avoid handling them bare-handed to prevent accidental defensive bites. If relocation is necessary, gently guide the spider into a container using a piece of cardstock.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution worldwide in temperate regions. Commonly found indoors in houses, basements, garages, and outdoors under rocks, logs, tree bark, and around human structures.
Behavior & Temperament
Timid and non-aggressive. They spend most of their time hanging motionless upside down in their webs. When disturbed, they typically drop to the ground or retreat rather than bite.
Diet & Prey
Primarily preys on crawling and flying insects such as flies, mosquitoes, roaches, and woodlice, as well as other spiders.
Seasonal Activity
Active year-round indoors, with peak mating and web-building activity often observed during late summer and autumn.
Description
Steatoda grossa, commonly known as the false black widow, is a frequent indoor companion that often startles homeowners due to its glossy, bulbous, dark appearance resembling a true widow spider. Despite this resemblance, it is a harmless and beneficial household resident that quietly helps control pest insect populations.
Key Features
Glossy, globose, dark purple-brown to black abdomen, lack of a red hourglass marking, and irregular cobweb construction in human habitations.
Similar Species
True Black Widow (Latrodectus spp.), which can be distinguished by the characteristic red or orange hourglass marking on the underside of the abdomen and a less glossy, more velvety black texture.
Life Cycle
Females produce papery silk egg sacs containing dozens to hundreds of eggs. Spiderlings hatch and disperse via ballooning or crawling. Adults can live for several years under favorable conditions.
Ecological Importance
Acts as a natural predator and pest control agent in and around human habitations, helping to keep populations of flies, roaches, and other insects in check.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and often thriving alongside human development.
Interesting Facts
Despite being called false widows, they are known to occasionally prey on true widow spiders if they happen to invade their webs.
Photography Tips
Use macro lenses with diffused natural or artificial lighting to highlight the glossy texture of the abdomen without causing harsh reflections. Shoot from the side for accurate profile shapes.
Identified: 2026-09-22T22:09:57.717183