Parasteatoda tepidariorum (C. L. Koch, 1841)

House spider

The cobweb spider in the corner of your basement window, harmless, and it eats other bugs.

Order: Araneae
Family: Theridiidae
Group: Spiders
Ontario status: Established, common indoor spider across Ontario

Why it matters

It is a free pest controller, each spider eats flies, mosquitoes, and other small insects all year. Its venom is not medically significant to people or pets. Most 'house spider problems' are really just dusty webs.

Origin

Probably South America originally; now lives with humans on every continent. It followed us indoors centuries ago.

Behavior

Nocturnal and sedentary. Spends almost its whole life in one web, rushing out to wrap anything that blunders into the silk. Active year-round indoors.

Living conditions

Dry, undisturbed indoor corners, window frames, basement joists, behind furniture, garages. Builds messy cobwebs and sits in them upside down waiting for prey.

Signs of presence

Messy, irregular cobwebs in upper corners, window frames, and basement ceilings
Small tan papery egg sacs (pea-sized) tucked into the webbing
Tiny spiderlings ballooning or clustered near a web in spring
Mottled brown spiders hanging belly-up in webs at night

Weaknesses

Completely dependent on its web, destroy the web and it must spend days rebuilding before it can feed
Cannot survive long outdoors in Ontario winters; it is an indoor obligate here
Vulnerable to simple vacuuming of webs and egg sacs
Needs a steady supply of small flying insects, reduce those and the spiders leave on their own

Myths and facts

Myth House spiders are dangerous and their bites need treatment.
Reality Bites are vanishingly rare and medically insignificant. This spider would rather drop from its web and play dead than bite.

Research notes

Morphology

Female body length 5-8 mm, male 4-5 mm; leg span up to ~20 mm. Mottled brown carapace and abdomen with variable chevron pattern; long thin legs with fine hairs. Abdomen globose, typical theridiid profile.

Diagnostics

Confirm by the combination of messy three-dimensional cobweb, mottled (never glossy black) abdomen, and tan papery egg sacs held in the web. Genitalia examination definitive for species.

Easily confused with

False widow spiders (Steatoda spp.) Steatoda is glossier, darker, and more uniformly colored with a rounder, harder-looking abdomen; house spiders are mottled and matte.
Cellar spider (Pholcus phalangioides) Cellar spiders have a tiny cylindrical body with absurdly long thin legs; house spiders have a large globose abdomen.

Life cycle

Adult: Females live 1-2 years indoors; males shorter-lived, wander in search of mates
Egg: 100-200 eggs per tan papery sac; female produces multiple sacs; sacs guarded in the web
Egg to adult: 2-4 months at room temperature; slower in cool basements
Generations per year: 2-3 indoors; continuous breeding year-round in heated buildings
Nymph or larva: Spiderlings emerge after 2-4 weeks (warmth dependent), disperse within days

Development

Egg to spiderling to adult through 5-7 molts; no true metamorphosis. Spiderlings disperse by ballooning on silk threads.

Reproduction

High fecundity: several egg sacs per female lifetime, each 100-200 eggs. Males cohabit female webs; mating often ends with the male being eaten.

Distribution

Global: Cosmopolitan synanthrope, on every continent except Antarctica
Native range: Probably South America
Ontario: Established province-wide wherever there are heated buildings; indoor obligate

Ecology

Generalist predator of small flying and crawling insects. Keystone indoor predator in Ontario homes; itself preyed on by cellar spiders and jumping spiders. Cannot establish outdoors in Ontario climate.

Resistance

Unknown, not a pesticide target species; no documented resistance literature.

IPM implications

Monitoring: web counts in undisturbed areas index the population. Tolerance is the rational default, it suppresses flies and other pests. Where webs are unacceptable (food plants, clean rooms), vacuum webs and sacs and seal entry points for the prey insects. Never a candidate for broadcast treatment.

Chemical ecology

Venom contains neurotoxic peptides effective on insect prey; not medically significant to mammals. Silk is a cobweb type with sticky gumfoot threads for snaring walking prey.

Genetics and DNA

Reference genome published (Parasteatoda tepidariorum), a major evo-devo model organism for spider embryology and silk-gene studies.

Taxonomy

Order Araneae, family Theridiidae (cobweb spiders). Authority (C. L. Koch, 1841). Formerly placed in Achaearanea; molecular work consolidated it in Parasteatoda.

Open questions

Exact native range still debated; degree of local adaptation to cold buildings unstudied.

References

Foelix, R.F. (2011). Biology of Spiders, 3rd ed., Oxford University Press.
Ebeling, W. (1978). Urban Entomology, University of California, Riverside.