False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a generally globose abdomen, weak or absent leg spines, and a comb-like row of serrated bristles on the tarsus of the fourth leg used to pull silk from the spinnerets.
Physical Description
The spider has a glossy, bulbous, egg-shaped abdomen and a relatively small cephalothorax. The body appears smooth with minimal hair compared to larger tarantulas or wolf spiders. It exhibits slight sexual dimorphism, with females being significantly larger and more rounded than the slender, longer-legged 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 roughly 20 to 25 mm. The specimen in the image appears to be a medium-sized adult or a late-stage subadult.
Coloration & Markings
Deep purplish-brown to blackish base coloration with distinctive pale yellowish or creamy markings on the dorsal abdomen, often forming geometric chevrons, crescents, or a triangular spot near the front. The legs show faint darker banding.
Web Type
Builds a three-dimensional, irregular tangle web, commonly known as a cobweb. These webs are constructed in dark, sheltered corners near the ground or in structural crevices, featuring sticky vertical threads extending to the surface to snag crawling insects.
Eye Arrangement
Eight small, dark eyes arranged in two parallel rows of four across the front of the cephalothorax, typical of the Theridiidae family, consisting of lateral pairs and a median quadrangle.
Leg Characteristics
Long, slender, tapering legs with subtle dark banding and sparse spination. The legs lack heavy claw tufts but feature the specialized comb-like serrated setae on the fourth pair of legs characteristic of comb-footed spiders.
Venom & Safety Information
Venom Information
Neurotoxic venom, but relatively mild compared to true widow spiders (Latrodectus). It is generally not medically significant to humans, though bites can cause localized pain, redness, and mild swelling.
Medical Significance
Low medical significance. While capable of biting if pressed directly against human skin, their venom causes only minor localized symptoms that typically subside within hours without lasting effects. Systemic illness is extremely rare.
Safety Recommendations
Avoid direct handling with bare hands. If found inside living areas, gently coax the spider into a jar using a piece of cardstock and relocate it outdoors. Wear gloves when clearing out dark, undisturbed storage spaces.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution across temperate regions worldwide, commonly found indoors in dark corners, basements, and garages, as well as outdoors under rocks, logs, bark, and within hollow spaces of walls or fences.
Behavior & Temperament
Timid, nocturnal, and non-aggressive. When disturbed, they typically retreat rapidly into a hiding spot, curl into a defensive ball, or drop from the web on a silken thread rather than bite.
Diet & Prey
Generalist predators feeding primarily on crawling and flying insects, including woodlice, flies, beetles, cockroaches, and occasionally other spiders. Prey is subdued with sticky silk and venom before being consumed.
Seasonal Activity
Active year-round indoors, with peak visibility and wandering adult males commonly observed during late summer and autumn when they leave their webs in search of mates.
Description
The False Black Widow (Steatoda grossa) is a frequent indoor companion often mistaken for its dangerous relative, the true black widow. Featuring a shiny, globular body with pale geometric markings against a dark backdrop, this cobweb weaver is a master of quiet persistence in dark corners and crevices. While harmless to humans and beneficial as a natural pest controller, its presence reminds us of the fascinating micro-ecosystems thriving right inside our homes.
Key Features
Glossy, bulbous abdomen, distinctive pale yellowish or whitish geometric markings or crescents on the upper surface, dark brown-to-purple coloration, and placement in an irregular 3D cobweb in a sheltered indoor or outdoor nook.
Similar Species
True Black Widow (Latrodectus spp.), which features a solid shiny black body often with a distinct red hourglass or red spots underneath, lacking the pale dorsal geometric chevrons typical of Steatoda grossa.
Life Cycle
Females construct tough, silken egg sacs containing dozens to hundreds of eggs, guarding them until they hatch. Spiderlings disperse via ballooning or crawling. Molting occurs multiple times throughout their development, and females can live for several years.
Ecological Importance
Acts as an effective natural pest control agent in residential and natural environments by consuming numerous nuisance insects, house pests, and potential disease vectors, helping to regulate local invertebrate populations.
Conservation Status
Not evaluated by the IUCN, but populations are secure, abundant, and expanding globally due to human commerce and adaptation to structural environments.
Interesting Facts
Despite the intimidating name 'False Black Widow', these spiders frequently prey on true black widows if they encounter them, successfully subduing the more notorious species using their specialized sticky silk.
Photography Tips
Use a macro lens or a smartphone macro attachment with adequate lighting or an external ring light. Capture a dorsal view to highlight the geometric markings and ensure a safe distance of a few inches to avoid startling the spider.
Identified: 2026-10-19T16:53:51.842866