Overview
The common house spider (Parasteatoda tepidariorum), also called the American house spider, is the spider most Ontario homeowners are actually looking at when they say “there’s a spider in the corner.” It’s a small, unremarkable brown spider that builds the messy, irregular cobwebs you find in ceiling corners, garages, basements, and around window frames. It is completely harmless — it eats flies, moths, and other insects — but it’s a relentless web-builder and a prolific breeder, which is why a home that tolerates a few in spring can look neglected by late summer. Understanding this species is the key to understanding almost every “spider problem” in an Ontario home.
Identification
The common house spider is 5–8 mm in body length — roughly a quarter-inch, not counting legs — and brown to tan with a rounded, teardrop-shaped abdomen marked by vague chevron (V-shaped) patterns. It characteristically hangs upside down in its web. The legs are often faintly banded. Its web is the giveaway: a tangled, three-dimensional cobweb with no organized pattern, unlike the neat wheel of an orb-weaver.
It’s a smaller, tamer animal than the ground-running wolf spider people also find indoors. The look-alike people most often confuse it with is the cellar spider, the true “daddy long-legs.”
| Feature | House Spider | Cellar Spider |
|---|---|---|
| Body size | 5–8 mm, rounded/teardrop | 7–8 mm, small and slender |
| Legs | Proportional, faintly banded | Extremely long, thin, delicate |
| Web | Dense, tangled cobweb | Loose, sparse tangle |
| Where | Corners, garages, window frames | Damp basements, crawl spaces |
| Posture | Hangs upside down, compact | Hangs in open, legs splayed wide |
Life Cycle
Females produce round, brown, papery egg sacs — each holding several hundred eggs — and suspend them in the web. A single female can create up to 17 sacs over her lifetime, more than 3,700 eggs in total. Spiderlings disperse on short silk threads, mature over a summer, and the survivors overwinter in sheltered indoor spaces. Because the species lives indoors year-round, generations overlap and a small tolerated population compounds quickly.
Habitat & Behaviour
House spiders are sit-and-wait predators. They anchor a tangled web in an undisturbed spot with good “hunting” — near a light that draws insects, a vent, or a window — and wait for prey to blunder in. They favour protected sites in and around buildings: ceiling and wall corners, garages, sheds, basements, attics, and the underside of decks and eaves. They readily abandon a web and rebuild elsewhere if a spot stops producing food, which is why webs seem to migrate around a room.
Diet
They eat whatever the web catches: house flies, fruit flies, fungus gnats, mosquitoes, moths, and other small insects — including, at times, other spiders. This is the same insect-driven pattern that pulls spiders indoors during humid Ontario summers. This is the crucial link for control: the size of your spider population is set by your insect population. A home with a lot of webs has a lot of insect prey feeding them.
Signs of Infestation
- Recurring cobwebs in the same corners within days of clearing — the single most reliable sign of an established population.
- Round, papery brown egg sacs suspended in webs, especially in garages and basements.
- Cast skins and insect debris collecting below webs.
- Spiders visible day and night in ceiling corners, window frames, and around exterior lights.
Damage Caused
None structural. House spiders don’t chew wood, wiring, insulation, or fabric. The “damage” is entirely aesthetic — webbing and egg sacs on ceilings, eaves, and light fixtures that make a well-kept home look neglected, and the general unease of a web-covered porch or basement.
Health Risks
Minimal and worth stating plainly. The common house spider is harmless. It can bite if pressed against skin — trapped in clothing or a glove — but bites are uncommon and typically no worse than a mild bee sting, with no medically significant venom. For a commercial kitchen or storefront, visible webbing is more a sanitation-appearance and inspection issue than a safety one.
Seasonal Activity in Ontario
Because it lives indoors, the common house spider can appear in any month, but activity follows a clear pattern. Numbers build through spring, climb in humid June as insect prey moves indoors, and peak in August and September when the year’s hatchlings reach full size and males roam in search of mates. Basements, garages, and low-traffic rooms hold populations through winter. GTA homes in Mississauga and Oakville see the same late-summer surge every year.
Where They Hide
Ceiling and wall corners, window and door frames, garages, sheds, basements, crawl spaces, attics, and the underside of decks, eaves, and soffits. Anywhere undisturbed, sheltered, and near an insect food source — which describes most of a house’s forgotten corners.
How They Enter Homes
Many never entered — they hatched inside. Those that do come from outside slip through gaps around windows, door sweeps, vents, and utility penetrations, or ride in on boxes, firewood, and plants. Because most of the population is already indoors, exclusion matters less for house spiders than reducing the insect prey and harbourage that sustain them.
Prevention Tips
- Vacuum, don’t brush — a hose attachment removes the web, egg sacs, and spider; a broom just smears silk and leaves the sac.
- Switch exterior bulbs to warm/yellow LED so fewer insects gather at doors and windows for spiders to hunt.
- Seal gaps around windows, door sweeps, vents, and pipe penetrations.
- Clear clutter from basement, garage, and storage corners where webs go unnoticed.
- Reduce indoor humidity and fix damp spots that draw the insects spiders feed on.
- De-web regularly — consistent removal discourages rebuilding in the same spots.
The full web-removal and prevention playbook covers the details, including why a vacuum beats a broom every time.
DIY vs. Professional Treatment
For a single web, a vacuum ends it. The trouble is that visible spiders are a fraction of an established indoor population living in wall voids and corners, and store sprays don’t reach them — so webs return within days. Professional treatment dewebs accessible eaves and fixtures, treats the harbourage where spiders shelter, and knocks down the insect food supply so the whole chain drops at once. Sani IQ’s spider control service backs this with a Pest-Free-Or-It’s-Free guarantee. The honest read: DIY isn’t about product cost, it’s about whether you want to spend the season on a ladder clearing eaves that re-web by Wednesday. See the 2026 cost breakdown to weigh it, or get a free quote to start.
References
- Penn State Extension — Common House Spider
- University of Minnesota Extension — Common House Spider
- Burke Museum — Spider Myths
Last updated: July 16, 2026 · Reviewed by Sani IQ licensed technicians