False Black Widow, Cobweb Spider, Cupboard Spider
Steatoda grossa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded, bulbous abdomen, comb-like serrated bristles on the tarsus of the fourth leg used to pull silk from the spinnerets, and an irregular tangle web.
Physical Description
The spider has a compact body featuring a relatively small, oval cephalothorax and a high, domed, bulbous abdomen. The overall texture is smooth with a slightly glossy sheen, characteristic of many theridiids. Sexual dimorphism is present, with females being notably larger, rounder, and bulkier than the slenderer males.
Size Estimate
Body length typically ranges from 6 to 10.5 mm for females and 4 to 6 mm for males, with a leg span around 20 to 30 mm. The specimen in the image appears to be an adult or sub-adult of average household size.
Coloration & Markings
Base coloration ranges from deep purplish-brown to dark charcoal black, sometimes appearing nearly maroon or reddish-brown. The abdomen often features subtle, lighter pale yellowish or greyish markings, sometimes forming chevron patterns, spots, or a faint band across the front, though these markings can be very dark and hard to see against the dark background in low light.
Web Type
Builds an irregular, three-dimensional tangle web commonly known as a cobweb. These webs are constructed in dark, undisturbed corners, often near ground level or high up in ceiling corners, consisting of sticky, haphazard threads designed to entangle walking insects.
Eye Arrangement
Equipped with eight small eyes arranged in two rows of four, typical of the family Theridiidae. The eyes are generally uniform in size and sit closely together on a slightly raised tubercle on the anterior cephalothorax.
Leg Characteristics
Legs are relatively long, thin, and taper smoothly, showing faint darker banding in some individuals. They lack heavy spination but are equipped with specialized comb-like structures on the hind tarsi used for manipulating silk. The legs are typically splayed outward when resting in the web.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom (specifically latrotoxin-like compounds, though much milder than true widow spiders). While bites can cause localized pain, redness, and mild systemic symptoms like malaise, they are generally not dangerous to humans.
Medical Significance
Low medical significance. Bites are rare and usually only occur if the spider is trapped directly against human skin (such as being squeezed in clothing). Symptoms are generally localized and resolve without lasting effects, though rare cases can produce mild flu-like symptoms.
Safety Recommendations
Avoid handling with bare hands; if removal is necessary, gently coax the spider into a container using a piece of cardstock and release it outdoors. Seal home entry points to reduce indoor populations if desired.
Habitat & Behavior
Habitat & Range
Found globally in temperate and subtropical regions, frequently associated with human habitations. They prefer dark, damp, protected areas such as basements, crawlspaces, garages, under furniture, and in high ceiling corners indoors, as well as under rocks and bark outdoors.
Behavior & Temperament
Timid, docile, and non-aggressive. They spend most of their time hanging motionless upside down in their webs. When disturbed, they typically retreat quickly into a crevice or drop to the ground and play dead rather than bite.
Diet & Prey
Feeds primarily on crawling and flying household insects, including ants, woodlice, roaches, flies, and other spiders. Prey stumbling into the sticky web is quickly wrapped in silk and immobilized with venom.
Seasonal Activity
Active year-round indoors where climate-controlled environments provide stable temperatures. Peak mating and wandering activity often occurs in late summer and autumn.
Description
The False Black Widow is a frequent indoor companion that often goes unnoticed in quiet corners and high ceilings. Recognized by its glossy, bulbous, dark body, it constructs messy cobwebs where it waits patiently for passing prey. While its superficial resemblance to the true black widow can cause unwarranted alarm, it is a peaceful, beneficial resident that helps control household insect populations.
Key Features
Rounded, glossy bulbous abdomen; deep brownish-black coloration; absence of a bright red hourglass marking; preference for high, dark ceiling corners or crevices indoors; construction of a messy, irregular cobweb.
Similar Species
True Black Widow (Latrodectus species) - distinguished by the presence of a distinct red or orange hourglass on the underside of the abdomen and a jet-black, velvety matte texture rather than a glossy brownish sheen.
Life Cycle
Females produce brownish, papery egg sacs containing dozens to hundreds of eggs, often hanging them within the web. Spiderlings hatch and disperse via ballooning or crawling short distances. Lifespan for females can reach several years under favorable indoor conditions.
Ecological Importance
Acts as an effective natural pest control agent within human dwellings and outbuildings, significantly reducing populations of nuisance insects and potential disease vectors.
Conservation Status
Not evaluated by the IUCN, but secure, widespread, and abundant throughout its global introduced and native ranges.
Interesting Facts
Despite their common name, False Black Widows are capable of preying on true black widows if the opportunity arises. They are thoroughly cosmopolitan and have successfully hitchhiked around the globe through international commerce.
Photography Tips
Use macro lenses or smartphone macro settings with adequate side-lighting to reveal subtle abdominal patterns and the glossy texture of the cephalothorax. Maintain a steady hand as indoor lighting can be dim.
Identified: 2026-09-05T09:11:25.890161