False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae
Physical Description
The spider has a glossy, bulbous, globular abdomen and a smaller, distinct cephalothorax. The overall body is smooth and appears somewhat leathery. Females are significantly larger and rounder than males, which have narrower abdomens and longer legs relative to their body size.
Size Estimate
Body length typically ranges from 6 to 10.5 mm for females and 4 to 6 mm for males, with a total leg span reaching up to 20 to 30 mm.
Coloration & Markings
Deep purplish-brown to glossy black overall, often featuring subtle lighter yellowish, greyish, or reddish-brown markings, sometimes forming pale crescent shapes or bands on the anterior portion of the dorsal abdomen.
Web Type
Irregular tangle web (cobweb) constructed in dark, protected crevices, corners, or near ground level indoors and in outbuildings.
Eye Arrangement
Eight small eyes arranged in two rows of four, typical of the Theridiidae family, with lateral eyes set close together on small tubercles.
Leg Characteristics
Long, slender legs with minimal spination, featuring faint darker banding on some segments. They lack specialized heavy claw tufts and typically rest flat against surfaces or within their web structure.
Venom & Safety Information
Venom Information
Contains neurotoxic components, but the venom is relatively weak compared to true black widows and poses minimal systemic threat to humans.
Medical Significance
Minor medical significance. Bites are rare and usually only occur when pressed directly against human skin. Symptoms typically involve localized pain, redness, and mild swelling lasting a few days, though rare systemic reactions (steatodism) with nausea and headache have been documented.
Safety Recommendations
Avoid direct handling with bare hands. Relocate unwanted indoor specimens using a container and piece of paper. Clean dark corners regularly to discourage web building.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution globally. Commonly found in human habitations, basements, garages, under furniture, and outdoors under logs, bark, and stone walls.
Behavior & Temperament
Timid, nocturnal, and non-aggressive. When disturbed, they typically retreat rapidly into their web or drop to the ground and play dead.
Diet & Prey
Generalist predator feeding on crawling and flying insects, woodlice, and occasionally other spiders trapped in its sticky web.
Seasonal Activity
Active year-round indoors, with peak wandering activity during late summer and autumn as males search for females.
Description
Steatoda grossa, commonly known as the False Black Widow, is a frequent indoor companion that often startles homeowners due to its superficial resemblance to dangerous widow spiders. With its glossy, bulbous body and preference for dark corners, this stealthy cobweb weaver plays an important role in controlling household insect pests.
Key Features
Glossy, bulbous, dark brown to black abdomen lacking any red hourglass shape, combined with an irregular cobweb and lack of fierce defensive behavior.
Similar Species
Latrodectus species (True Black Widows), which feature the distinctive red hourglass marking on the underside of the abdomen. Steatoda triangulosa, which has a distinct triangular or zigzag pattern on the back.
Life Cycle
Females produce papery, brownish egg sacs containing up to several hundred eggs. Spiderlings hatch after a few weeks, molt multiple times, and can live for several years in favorable conditions.
Ecological Importance
Acts as an effective natural pest controller in domestic and peri-domestic environments by reducing populations of flies, roaches, and other insects.
Conservation Status
Not evaluated by the IUCN, but highly secure and widespread globally due to its close association with human habitations.
Interesting Facts
Despite being called the False Black Widow, Steatoda grossa can occasionally prey on true black widows if they wander into its web.
Photography Tips
Use macro lenses with side-lighting to highlight the glossy texture of the abdomen and capture subtle dorsal patterns without disturbing the spider.
Identified: 2026-08-27T02:18:49.257102