Cobweb Spider, False Black Widow, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae
Physical Description
The spider has a bulbous, globular abdomen and a smaller cephalothorax. The body is relatively smooth with fine hairs. Marked sexual dimorphism exists, with females being larger and rounder, and males being smaller with longer legs.
Size Estimate
Body length ranges from 6 to 10.5 mm for females and 4 to 6 mm for males, with a leg span up to 20 to 30 mm.
Coloration & Markings
Base coloration ranges from deep purple-brown to black, sometimes with lighter brownish or yellowish markings, including pale triangular spots or bands on the dorsal abdomen.
Web Type
Constructs a sticky, irregular tangle web (cobweb) in dark, undisturbed corners, near ground level or inside structures.
Eye Arrangement
Eight small eyes arranged in two rows of four, typical of the Theridiidae family, set on dark tubercles.
Leg Characteristics
Legs are moderately long, slender, and brownish, generally lacking heavy spination but possessing comb-like serrated bristles on the tarsus of the fourth pair of legs.
Venom & Safety Information
Venom Information
Contains neurotoxic components (latrotoxin-like), though significantly less potent than true black widows. Bites are rarely medically significant.
Medical Significance
Not considered dangerous to humans. A bite can cause mild local pain, redness, and swelling, occasionally accompanied by mild systemic symptoms like malaise.
Safety Recommendations
Wear gloves when cleaning dark, undisturbed spaces. If relocation is needed, gently guide the spider into a container using a piece of paper.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution; found worldwide in temperate regions, frequently inhabiting dark corners of homes, garages, sheds, under rocks, and bark outdoors.
Behavior & Temperament
Docile and non-aggressive; hangs upside down in its cobweb, retreating when disturbed and only biting if firmly trapped against human skin.
Diet & Prey
Feeds primarily on crawling and flying insects, including woodlice, flies, and occasionally other spiders caught in its sticky web.
Seasonal Activity
Active year-round indoors, with peak outdoor visibility and mating occurring during the warmer summer and autumn months.
Description
Steatoda grossa, commonly known as the false black widow, is a frequent indoor companion often mistaken for its more dangerous relatives. With its glossy, bulbous abdomen and dark coloration, it quietly maintains order in basement corners by managing household insect pests.
Key Features
Globular, shiny abdomen, lack of a red hourglass marking, dark brown to black coloration, and creation of messy tangle webs in corners.
Similar Species
Latrodectus species (True Black Widows), which feature the distinctive red hourglass marking on the underside of the abdomen.
Life Cycle
Females produce spherical silk egg sacs containing up to several hundred eggs. Spiderlings disperse via ballooning or crawling after hatching; adults can live for several years.
Ecological Importance
Serves as an effective natural predator of insect populations in both domestic and natural habitats, helping control potential pest species.
Conservation Status
Not evaluated by the IUCN, but populations are secure, abundant, and widely distributed globally.
Interesting Facts
Despite the frightening moniker 'false widow', these spiders are beneficial pest controllers and actively help reduce populations of woodlice and other household pests.
Photography Tips
Use macro lenses with adequate lighting to capture the shiny dorsal markings and subtle coloration without disturbing the spider in its web.
Identified: 2026-08-18T14:54:56.328830