Common American House Spider
Parasteatoda tepidariorum
Theridiidae (Cobweb Spiders), Order Araneae. Key family characteristics include a globular abdomen in females, the presence of a comb-like row of setae (serrated bristles) on the tarsus of the fourth leg used for pulling silk from the spinnerets, and untidy, three-dimensional tangle webs.
Physical Description
The spider has a bulbous, oval-to-round abdomen that is notably high and rounded, a smaller cephalothorax, and slender, tapering legs. The body surface is finely hairy. Distinct sexual dimorphism is present; females have significantly larger, rounder abdomens and shorter legs relative to their body size, while males are smaller, slender, and feature longer legs and enlarged palps.
Size Estimate
Body length ranges from 5 to 8 millimeters for females and 3.8 to 6 millimeters for males, with a total leg span reaching approximately 1.5 to 2.5 centimeters. This specimen appears to be an adult female accompanied by a smaller male nearby.
Coloration & Markings
Base coloration varies from yellowish-brown to dark brown or grayish. The abdomen typically features mottled patterns, chevron markings, or dark spots, often with light edges. The legs are yellowish or brownish with distinct dark bands or rings.
Web Type
Builds a classic cobweb or tangle web, which is an irregular, three-dimensional scaffold of sticky silk threads constructed in corners, crevices, and near structural joints. The web often includes a dome-shaped retreat area where the spider hides.
Eye Arrangement
Has eight small eyes arranged in two slightly curved horizontal rows of four each (anterior and posterior rows), with the lateral eyes often touching or closely grouped on small tubercles.
Leg Characteristics
Legs are long, thin, and tapering, featuring distinct dark banding or annular rings. They lack heavy spination but possess the characteristic comb-like serrated bristles on the fourth tarsus used for manipulating web silk.
Venom & Safety Information
Venom Information
Possesses neurotoxic venom designed to immobilize small invertebrate prey. The venom has very low toxicity to humans and is generally ineffective against large mammals.
Medical Significance
Harmless to humans. Bites are extremely rare because the spiders are docile and their chelicerae are small. If a bite occurs, it typically results in only minor, localized irritation, slight redness, or mild swelling similar to a mosquito bite.
Safety Recommendations
No special safety measures are required as they are completely harmless. If relocation is desired, gently guide the spider into a container using a piece of paper and release it outdoors.
Habitat & Behavior
Habitat & Range
Cosmopolitan distribution, found worldwide in association with human habitations. Prefers dark, protected microhabitats such as corners of rooms, basements, garages, outbuildings, crawl spaces, and exterior sheltered walls near doors and windows.
Behavior & Temperament
Timid and non-aggressive. It hangs upside down in its web waiting for prey. When disturbed, it typically retreats to a corner, drops from the web on a safety line, or plays dead rather than biting.
Diet & Prey
Feeds primarily on crawling and flying insects such as flies, mosquitoes, gnats, ants, beetles, and occasionally other spiders. Traps prey in the sticky lines of the tangle web, then immobilizes and wraps them with silk.
Seasonal Activity
Active year-round indoors in climate-controlled buildings, with peak activity, mating, and web expansion occurring during the warmer spring and summer months.
Description
The Common American House Spider is a familiar and harmless indoor neighbor. Recognized by its bulbous, patterned abdomen and messy web in structural corners, it serves as a silent pest controller, quietly managing populations of household insects without threatening humans.
Key Features
Bulbous, high-rounded abdomen, mottled brown or grayish coloration with chevron patterns, banded legs, and an irregular three-dimensional tangle web built in corners.
Similar Species
Can be confused with the Brown Recluse (Loxosceles reclusa) due to similar brown coloration. However, Loxosceles lacks the bulbous abdomen, banded legs, and messy web, featuring instead a violin-shaped marking on the cephalothorax and six eyes arranged in pairs.
Life Cycle
Females produce brownish, pear-shaped or spherical silken egg sacs containing hundreds of eggs, attaching them near the web. Spiderlings hatch after a couple of weeks, disperse via ballooning or crawling, undergo multiple molts to reach maturity, and can live for over a year.
Ecological Importance
Acts as an effective natural pest controller in homes and gardens, significantly reducing populations of nuisance and disease-vector insects like flies and mosquitoes, while serving as prey for larger predators.
Conservation Status
Not evaluated by the IUCN, but populations are extremely secure, widespread, and abundant globally due to their successful adaptation to human-modified environments.
Interesting Facts
These spiders can adjust the tension of their web threads to detect different types of vibrations caused by struggling prey versus falling debris. They often maintain multiple webs in close proximity if food is abundant.
Photography Tips
Use macro lenses with a ring flash or diffused lighting to highlight the intricate abdominal patterns and banded legs. Photograph from the side or slightly above while the spider is stationary in its web.
Identified: 2026-10-13T23:28:05.729305