False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae
Physical Description
The spider has a bulbous, oval-shaped abdomen that is distinctly plump and glossy, paired with a smaller cephalothorax. The body texture is smooth to slightly leathery. Females are notably larger and more robust than males, which have slimmer abdomens and longer legs relative to their body size.
Size Estimate
Body length ranges from 6 to 10.5 mm for females and 4 to 6 mm for males, with a total leg span reaching roughly 20 to 30 mm.
Coloration & Markings
Base coloration ranges from dark purple-brown to nearly black, often featuring pale yellowish, cream, or whitish triangular and crescent-shaped markings on the dorsal side of the abdomen. The legs are typically a lighter brownish-orange, sometimes showing faint darker banding.
Web Type
Builds an irregular, sticky cobweb or tangle web in dark, protected corners, usually close to the ground, under furniture, or within structural crevices.
Eye Arrangement
Consists of eight small eyes arranged in two curved, roughly parallel horizontal rows of four across the front of the cephalothorax, typical of the family Theridiidae.
Leg Characteristics
Legs are moderately long, slender, and tapering, featuring fine hairs and slight spines. They lack specialized heavy scopulae or claw tufts, and the spider typically rests suspended upside-down in its tangle web.
Venom & Safety Information
Venom Information
Contains neurotoxic components (latrotoxin-like), though significantly weaker than that of true widow spiders (Latrodectus). Envenomation is generally mild in humans.
Medical Significance
Not considered medically significant. A bite may cause minor localized pain, redness, and swelling, occasionally accompanied by mild systemic symptoms like malaise, but severe complications are extremely rare.
Safety Recommendations
Avoid handling them bare-handed to prevent accidental bites. If relocation is necessary, gently guide the spider into a container using a piece of card. First aid for bites involves cleaning with soap and applying a cold compress.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, frequently found worldwide in temperate and subtropical regions. Inhabits human-made structures, basements, garages, outbuildings, as well as natural crevices under rocks and logs outdoors.
Behavior & Temperament
Docile and non-aggressive; relies on retreating into a nearby crevice or playing dead when disturbed. It is primarily nocturnal, spending daylight hours hidden near its web.
Diet & Prey
Feeds primarily on crawling and flying insects, including woodlice, flies, roaches, and occasionally other spiders, subduing larger prey using sticky silk from its web.
Seasonal Activity
Active year-round indoors, with peak visibility and mating activity typically occurring during the warmer summer and autumn months.
Description
Steatoda grossa, commonly known as the false black widow, is frequently mistaken for its dangerous relative due to its dark, glossy appearance and bulbous abdomen. However, it is a peaceful household resident that plays an active role in keeping indoor insect populations under control. Its striking pale markings against a dark backdrop make it easily recognizable to observant nature enthusiasts.
Key Features
Glossy, bulbous abdomen with pale cream or yellowish crescent and triangular markings, combined with a dark brownish body and the absence of a true red hourglass shape.
Similar Species
True Black Widow (Latrodectus species), which features a shiny jet-black body often marked with a distinctive red hourglass on the underside of the abdomen and lacks the pale dorsal stripes found in Steatoda grossa.
Life Cycle
Females produce papery, brownish egg sacs containing dozens to hundreds of eggs. Spiderlings hatch and disperse via ballooning or crawling. They undergo multiple molts over a lifespan of several years.
Ecological Importance
Acts as an effective natural pest controller in domestic and semi-natural environments, helping to regulate insect populations and serving as food for larger predators.
Conservation Status
Not evaluated by the IUCN, but populations are secure, widespread, and thriving globally alongside human habitations.
Interesting Facts
Despite the intimidating common name, false black widows are beneficial household predators that readily consume pests like woodlice and silverfish that other spiders ignore.
Photography Tips
Use macro lenses with adequate side lighting to highlight the glossy texture and pale patterns on the abdomen. Photograph from a slight side angle to accurately capture the body proportions.
Identified: 2026-10-11T20:02:58.459033