Triangulate Cobweb Spider, Triangle Spider
Steatoda triangulosa
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a rounded abdomen, comb-like structures on the hind tarsi used to pull silk, and typically building irregular, sticky tangle webs.
Physical Description
The spider features a glossy, bulbous, pear-shaped abdomen with a relatively small cephalothorax. The legs are thin and delicate in proportion to the body. There is minimal hairiness, giving it a smooth and shiny appearance characteristic of many cobweb spiders.
Size Estimate
Body length ranges typically from 3 to 6 millimeters for females, with males being slightly smaller. The total leg span can reach up to 15 to 20 millimeters. This specimen appears to be an adult.
Coloration & Markings
The base color of the cephalothorax and legs is yellowish-brown or orange-brown. The distinctive hallmark is the abdomen pattern, featuring a yellowish-white background overlaid with a series of dark, jagged, intersecting triangular or zigzag bands running down the dorsal side.
Web Type
Builds an irregular, messy tangle web, commonly known as a cobweb. These webs are constructed in dark, undisturbed corners, near baseboards, under furniture, or in cellars and outbuildings.
Eye Arrangement
Arranged in two horizontal rows of four eyes each, typical of the family Theridiidae. The eyes are relatively small, dark, and uniform in size, situated on a slightly raised area of the cephalothorax.
Leg Characteristics
The legs are long, slender, and thread-like, lacking prominent spines but equipped with a comb of serrated bristles on the fourth tarsus used for flinging silk over prey. They typically spread out flat or angled against the surface.
Venom & Safety Information
Venom Information
Possesses mild neurotoxic venom designed to quickly subdue small insect prey. It is not specialized for large vertebrates.
Medical Significance
Harmless to humans. Bites are extremely rare, typically occurring only if the spider is trapped directly against the skin. Symptoms are usually minor, localized, and short-lived, consisting of slight redness or mild pain.
Safety Recommendations
No special precautions needed beyond standard caution. If relocation is desired, gently guide the spider into a cup using a piece of cardstock and release it safely outdoors.
Habitat & Behavior
Habitat & Range
Widely distributed throughout Europe, parts of Asia, and introduced to North America where it is common in urban and suburban environments. It heavily favors human dwellings, basements, garages, and damp, dark microhabitats.
Behavior & Temperament
Docile, timid, and non-aggressive. When disturbed, it typically retreats rapidly into a hiding spot or drops from its web on a safety dragline. It is primarily nocturnal.
Diet & Prey
Feeds primarily on household arthropods, including ants, roaches, woodlice, flies, and crucially, other spiders such as hobo spiders and even potentially dangerous species like the brown recluse or black widow.
Seasonal Activity
Active year-round indoors, though mating and peak visibility often occur during the warmer summer and autumn months when adults wander in search of mates.
Description
The triangulate cobweb spider is a quintessential household arachnid easily recognized by the geometric zigzag pattern adorning its bulbous abdomen. Though small and unassuming, it acts as a silent and efficient guardian in basements and dark corners, helping control populations of pests and even other venomous spiders.
Key Features
Bulbous rounded abdomen marked with distinct, dark zigzag or triangular patterns forming a chain-like band down the back, paired with long, thin, unbanded legs and a shiny yellowish-brown body.
Similar Species
Can be confused with other Steatoda species (such as Steatoda grossa, the false black widow), which generally lack the distinct triangulated dorsal pattern, or young widow spiders (Latrodectus), which feature more prominent red spots or hourglass shapes without the sharp geometric triangles.
Life Cycle
Females produce papery, brownish silk egg sacs containing dozens of eggs, hiding them within or near the web. Spiderlings emerge and disperse via ballooning or crawling to nearby locations. Lifespan is typically around one year.
Ecological Importance
Serves as an effective natural pest control agent inside human habitations and outbuildings, helping regulate populations of crawling insects and potentially hazardous arachnids without chemical intervention.
Conservation Status
Not evaluated by the IUCN, but populations are secure, abundant, and widely distributed, frequently benefiting from human settlement and urban expansion.
Interesting Facts
Steatoda triangulosa is known for being a natural predator of the brown recluse spider (Loxosceles reclusa), successfully subduing larger and medically significant spiders by entangling them in tough, sticky cobweb silk.
Photography Tips
Use macro photography with a soft diffuser to avoid harsh reflections on the shiny abdomen. Shoot from a top-down angle to clearly capture the diagnostic geometric triangular patterns on the back.
Identified: 2026-09-03T15:29:49.187637