Steatoda triangulosa

Distinguished from black widows (Latrodectus spp.) by smaller size, lack of glossy black coloration, and the distinctive triangular pattern rather than an hourglass or spots. Differs from Steatoda grossa (false black widow) by the triangular abdominal pattern versus the more uniform or spotted pattern of S. grossa. Separated from Parasteatoda tepidariorum (common house spider) by smaller size and more defined abdominal markings; P. tepidariorum has a larger body and less distinct patterning. The dark reddish-brown cephalothorax and banded legs are additional distinguishing features.

Small-bodied cobweb spider with adult females 3.6–5.9 mm and males 3.5–4.7 mm in body length. Abdomen has a dirty white or beige background with a pair of bold, wavy, rusty to purplish-brown longitudinal lines forming a triangular pattern. Cephalothorax is dark reddish-brown. Legs are pale brown to yellowish with dark bands at the joints. Males have a more slender, leggy build compared to females. The overall leg span does not cover a U.S. dime or penny.

Strongly synanthropic, occupying dark, sheltered recesses in human-made structures. Frequently found in basements, cellars, garages, water meter boxes, window frames, and under bridges or in culverts where webs are protected from weather. Prefers locations with access to crevices for retreat when disturbed. In southern parts of its native range, occurs in natural habitats; in colder regions, restricted to human-associated environments.

Native to central and southern Europe, the Mediterranean region, and southern Russia through Central Asia, China, and Korea. Introduced to North America, where established from Massachusetts to Nebraska, Colorado, Utah, Oregon, and California, with gaps in the southwest and Florida. Also recorded from southern Ontario, Canada; Argentina; Canary Islands; and South Africa. Recently confirmed as established in Poland.

Mating occurs from late spring through early autumn. Adults may be encountered year-round in protected indoor environments. Activity appears continuous in suitable microhabitats without pronounced seasonal dormancy.

Preys on a variety of insects. Documented to capture Red Imported Fire Ant (Solenopsis invicta) in the southern United States, though not considered effective for biological control. Accepts small flies, beetles, and other arthropods that contact the web.

Females deposit approximately 30 eggs per sac, wrapped in an opaque white spherical sac with sheer fabric through which eggs are visible. Females may produce six or more egg sacs in their lifetime. Spiderlings emerge from egg sacs and disperse to build independent webs. Development and reproduction have been documented under laboratory conditions, though specific instar counts and developmental durations are not detailed in available sources.

Constructs irregular, tangled cobwebs with a more-or-less sheet-like central platform. Hangs upside down in the web. Web construction occurs over multiple nights, involving stereotyped behaviors: spiders move along structural threads, drop to attach to lower substrate, and coat the lowest portion with viscid silk on return, creating gumfooted lines. Constructs gumfooted lines in bouts with regular intervals between bouts. When disturbed, drops from the web and seeks refuge in nearby crevices. Tolerates proximity to webs of other cobweb weavers, cellar spiders, and even brown recluse spiders. Males court females in response to a ternary blend of contact pheromones on female webs.

Generalist predator of small insects and other arthropods in human-modified environments. Serves as prey for larger spiders and other predators. Documented as cohabitating with other spider species without aggression, though individual observations suggest occasional intraspecific cannibalism.

Common household spider that reduces populations of nuisance insects including fire ants. Not recognized as dangerously venomous; bites are unlikely to puncture human skin due to small size. Bites, when they occur, cause mild pain that subsides quickly. Occasionally mistaken for black widows, causing unnecessary concern. Sometimes kept as pets by hobbyists.

• Latrodectus spp. (black widows)Larger size; glossy black coloration; hourglass or spot patterns rather than triangular lines; medically significant venom
• Steatoda grossa (false black widow)More uniform purple-brown to black coloration with variable spotting; lacks distinct triangular abdominal pattern
• Parasteatoda tepidariorum (common house spider)Larger body size (~6–20 mm); less defined, more variable abdominal pattern; similar web structure but larger overall

Frequently mistaken for black widow spiders due to family relationship and dark coloration, but lacks dangerous venom and is too small to effectively bite humans. The triangular pattern is distinctive and not shared with widow spiders.

• synanthropic
• cobweb spider
• house spider
• introduced species
• non-venomous
• generalist predator

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
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