False Black Widow, Cupboard Spider, Industrial Spider
Steatoda grossa
Family Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a generally globose abdomen, comb-like serrated bristles on the tarsus of the fourth leg used for flinging silk over prey, and small, eight-eyed arrangements.
Physical Description
The spider has a glossy, bulbous, spherical abdomen and a relatively small cephalothorax. The body texture is smooth and leathery rather than heavily haired. This specimen is clearly an adult female, characterized by her heavily distended, plump abdomen filled with eggs.
Size Estimate
The body length of this adult female is approximately 6 to 10 millimeters, with a leg span of roughly 15 to 20 millimeters, making it a medium-sized theridiid spider.
Coloration & Markings
The base coloration of the abdomen is a rich reddish-brown or purple-brown, adorned with distinctive, irregular spots and blotches of pearlescent white or cream. The legs display alternating dark brown and pale yellowish-white bands.
Web Type
Builds an irregular, messy tangle web, commonly referred to as a cobweb. These webs are constructed in dark, sheltered crevices near ground level, utilizing sticky, dry silk threads designed to snare crawling insects.
Eye Arrangement
Has eight small eyes arranged in two parallel rows of four. The eyes are relatively uniform in size, spread across a slightly raised ocular tubercle on the anterior portion of the cephalothorax.
Leg Characteristics
Legs are moderately long and slender, featuring distinct dark and light banding patterns. They lack heavy spination, but possess the specialized serrated comb-like bristles on the fourth pair of legs characteristic of comb-footed spiders.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom containing latrotoxin-like components, though significantly milder than that of true widow spiders (Latrodectus). Envenomation is not life-threatening to humans.
Medical Significance
Minor medical significance. A bite can cause localized pain, redness, and swelling that typically resolves within a day. Systemic symptoms resembling mild latrodectism (steatodism) are rare, temporary, and rarely require medical intervention.
Safety Recommendations
Avoid direct handling with bare hands when cleaning dark corners or moving stored items. If found indoors, gently relocate the spider outside using a cup and a piece of card. Bites can be treated with a cold compress and antiseptic.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found worldwide in temperate and subtropical regions. Prefers dark, humid microhabitats such as under rocks, logs, bark, as well as anthropogenic structures like basements, crawlspaces, sheds, and outdoor furniture.
Behavior & Temperament
Docile and non-aggressive. It spends most of its time motionless in its retreat or web. When disturbed, it typically plays dead, drops to the ground, or retreats quickly, only biting as an absolute last resort if trapped against skin.
Diet & Prey
Feeds primarily on crawling and flying insects, including woodlice, flies, beetles, cockroaches, and occasionally other spiders. It wraps struggling prey in sticky silk before delivering a paralyzing bite.
Seasonal Activity
Active year-round in indoor environments, with peak outdoor visibility and mating occurring during the warm summer and autumn months. They overwinter as adults or juveniles sheltered in protected crevices.
Description
The False Black Widow is a frequent household guest that often goes unnoticed due to its secretive habits. Recognized by its glossy, bulbous, reddish-brown abdomen decorated with striking white spots, this cobweb weaver is a master of quiet pest control. Though its striking appearance and distant relation to true widows can cause unwarranted alarm, it is a timid creature that prefers to steer completely clear of human interaction.
Key Features
Glossy, globose reddish-brown abdomen; distinctive pearlescent white or yellowish spots on the dorsal surface; banded legs; lack of an hourglass marking.
Similar Species
True Black Widow (Latrodectus spp.), which features a shiny jet-black body often with a red hourglass marking underneath and lacks white dorsal spots. Steatoda triangulosa, which has a patterned zig-zag or triangular dorsal design instead of scattered white spots.
Life Cycle
Females construct tough, brownish silk egg sacs containing up to several hundred eggs, guarding them in the web. Spiderlings hatch, molt multiple times, and disperse via ballooning or crawling. Lifespan for females can reach several years.
Ecological Importance
Serves as an effective natural predator of household and garden insect pests, helping to naturally regulate populations of flies, roaches, and woodlice while acting as a food source for larger predators like birds and wasps.
Conservation Status
Not evaluated by the IUCN, but populations are secure, abundant, and widely distributed globally due to successful adaptation to human-modified environments.
Interesting Facts
Despite the intimidating common name, Steatoda grossa is frequently kept by researchers to study web architecture and venom chemistry. It is capable of subduing prey much larger than itself, including large beetles and mice, using its remarkably strong silk.
Photography Tips
Shoot from directly above to capture the striking white spot patterns on the abdomen. Use macro lighting to highlight the glossy texture of the exoskeleton, and maintain a calm approach to avoid startling the spider into dropping from its spot.
Identified: 2026-10-08T21:07:57.049845