Triangulate Cobweb Spider, Triangulate House Spider
Steatoda triangulosa
Theridiidae (Cobweb Spiders), Order Araneae
Physical Description
The spider has a glossy, bulbous, pear-shaped abdomen and a smaller, rounded cephalothorax. The legs are relatively long, thin, and taper smoothly, giving it a typical cobweb spider appearance.
Size Estimate
Body length ranges from 3 to 6 millimeters for females and slightly smaller for males, with a leg span of approximately 1.5 to 2 centimeters.
Coloration & Markings
The cephalothorax is yellowish-brown or orange-brown. The abdomen is yellowish-white to light brown, featuring a distinct diagnostic pattern of broken, dark purple-brown triangular or zig-zag markings down the dorsal side.
Web Type
Builds an irregular, sticky tangle web (cobweb) in corners of rooms, under furniture, or in sheltered outdoor areas like window frames and siding.
Eye Arrangement
Has eight small eyes arranged in two parallel rows of four, typical of the family Theridiidae, with lateral eyes often touching or closely grouped.
Leg Characteristics
Legs are slender, yellowish-brown, and prominently marked with dark brown or reddish-brown rings and bands at the joints.
Venom & Safety Information
Venom Information
Possesses mild neurotoxic venom used primarily to subdue small invertebrate prey. Not considered dangerous to humans.
Medical Significance
Not medically significant. Bites are rare, usually only occurring if the spider is directly trapped against human skin, and typically result in mild, localized pain or redness similar to a mild bee sting.
Safety Recommendations
No special precautions needed. If relocation is desired, gently guide the spider into a container using a piece of cardstock and release it outdoors.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found globally in temperate regions, frequently inhabiting human dwellings, cellars, garages, and sheltered outdoor architectural crevices.
Behavior & Temperament
Docile, highly non-aggressive, and strictly nocturnal or crepuscular. They retreat to a hiding spot near their web when disturbed.
Diet & Prey
Feeds on a wide variety of household and garden insects, including ants, flies, beetles, roaches, and occasionally other spiders.
Seasonal Activity
Active year-round indoors, with peak visibility and breeding activity during the warmer spring and summer months.
Description
The Triangulate Cobweb Spider is a common household resident, easily recognized by the striking geometric pattern on its bulbous abdomen. While often mistaken for more dangerous species due to its shape, it is a harmless and beneficial predator that helps control household pest populations.
Key Features
Distinctive purple-brown triangular zig-zag patterns on a yellowish-white bulbous abdomen, combined with banded legs and a preference for irregular cobwebs.
Similar Species
Steatoda grossa (False Black Widow) which is darker and lacks the distinct triangular dorsal pattern, and Latrodectus species (Black Widows) which are glossy black and feature a red hourglass rather than geometric markings.
Life Cycle
Females produce papery silk egg sacs containing dozens of eggs, hiding them within or near the web. Spiderlings hatch after a few weeks, molt multiple times, and mature within a year.
Ecological Importance
Acts as an effective natural pest control agent inside and around human habitations by intercepting and consuming nuisance insects.
Conservation Status
Not evaluated by the IUCN, but populations are secure, abundant, and widely distributed globally.
Interesting Facts
Despite being native to Eurasia, this species has successfully hitched rides with human commerce to establish thriving populations across North America and other parts of the world.
Photography Tips
Use macro settings or a macro lens with good natural side-lighting to highlight the intricate geometric markings on the dorsal abdomen.
Identified: 2026-08-03T18:41:31.843946