False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Family Theridiidae (Cobweb Spiders), Order Araneae
Physical Description
The spider has a rounded, bulbous abdomen and a smaller cephalothorax, typical of comb-footed spiders. The body is relatively smooth with short hairs, and females are notably larger and more robust than males.
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 25 mm. This appears to be an adult or sub-adult specimen.
Coloration & Markings
Coloration ranges from dark purple-brown to glossy black, sometimes with subtle lighter yellowish or grayish markings, chevron patterns, or pale bands on the abdomen.
Web Type
Builds an irregular, three-dimensional tangle web (cobweb) in dark, undisturbed corners, often near ground level or around structural joints.
Eye Arrangement
Features eight small eyes arranged in two distinct horizontal rows of four, typical of the Theridiidae family.
Leg Characteristics
The legs are slender, moderately long, and generally devoid of prominent spines, often matching the dark base coloration of the body.
Venom & Safety Information
Venom Information
Contains neurotoxic components, but the venom is relatively mild and not life-threatening to humans.
Medical Significance
Bites are rare and usually happen only when trapped against human skin. Symptoms include localized pain, redness, and mild swelling, occasionally causing systemic discomfort (steatodism) similar to a mild wasp sting.
Safety Recommendations
Avoid direct handling with bare hands; if relocation is necessary, gently guide the spider into a container using a piece of paper. First aid for bites involves cleaning the area and applying cold compresses.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, frequently found worldwide in temperate regions, inhabiting human structures, basements, crawlspaces, under furniture, and outdoor sheltered areas.
Behavior & Temperament
Non-aggressive and timid; hangs upside down in its web and typically retreats or curls into a ball when disturbed rather than attacking.
Diet & Prey
Feeds on various crawling and flying household insects, including woodlice, flies, beetles, and occasionally other spiders, using sticky silk lines to subdue prey.
Seasonal Activity
Active year-round indoors, with mating occurring primarily during the warmer spring and summer months.
Description
Steatoda grossa, commonly known as the False Black Widow, is a frequent indoor companion often mistaken for its more dangerous relative due to its glossy, bulbous dark body. Preferring quiet corners, this master of the cobweb plays a quiet yet effective role in household pest control.
Key Features
Glossy, bulbous dark abdomen without a bright red hourglass marking, combined with an irregular cobweb and a preference for indoor structures.
Similar Species
Latrodectus species (True Black Widows), which can be distinguished by the prominent red or orange hourglass marking on the underside of the abdomen.
Life Cycle
Females produce several silk-wrapped egg sacs containing up to 200 eggs each. Spiderlings disperse via ballooning after hatching, undergoing multiple molts to reach maturity within a year.
Ecological Importance
Acts as an effective natural pest controller in domestic and semi-natural environments by reducing populations of common household insects.
Conservation Status
Not evaluated by the IUCN, but populations are secure, abundant, and widespread globally due to human commensalism.
Interesting Facts
Despite the frightening moniker 'false widow', these spiders are beneficial pest controllers and can live for several years in protected indoor environments.
Photography Tips
Use a macro lens with good side lighting to highlight the glossy texture and subtle abdominal patterns. Maintain a safe distance and photograph against a neutral background.
Identified: 2026-08-28T10:50:39.955447