Overview
The cellar spider (family Pholcidae) is the pale, spindly spider hanging in a loose tangle of web in the corner of nearly every Ontario basement, garage, and crawl space. It’s the true “daddy long-legs” of the spider world — small body, absurdly long thread-thin legs — and the subject of one of the most persistent myths in all of pest lore: that it’s the most venomous spider on earth but can’t bite through human skin. That claim is flatly false, and clearing it up is worth doing because it’s the reason so many people fear a completely harmless animal. Cellar spiders are benign, beneficial, and easy to manage once you understand them.
Identification
The long-bodied cellar spider has a 7–8 mm body and remarkably long, thin, delicate legs that can span 50 mm, giving it a fragile, translucent look in pale tan to grey. It hangs upside down in a loose, irregular web in a sheltered corner, and when disturbed it bounces and vibrates rapidly — the “vibrating spider” behaviour that instantly identifies it. Females carry a loose bundle of eggs in their jaws rather than wrapping them in a dense sac.
Unlike the common house spider, whose legs are proportional to its body, the cellar spider’s legs are extraordinarily long and thread-thin. The confusion here isn’t with another spider so much as with two unrelated animals that share the “daddy long-legs” nickname.
| ”Daddy long-legs” | What it actually is | Web / silk? | Venom |
|---|---|---|---|
| Cellar spider | A true spider (Pholcidae) | Yes — loose basement web | Weak, harmless to people |
| Harvestman | Not a spider (Opiliones) | No silk at all | None — no venom glands |
| Crane fly | A flying insect | No | None |
Only the cellar spider spins the basement webs. The harvestman — a single-bodied outdoor arachnid — and the crane fly are different creatures entirely.
Life Cycle
Cellar spiders breed indoors year-round in Ontario’s heated basements. The female produces a loose clutch of eggs held together with a few silk threads and carries it in her chelicerae (jaws) until the spiderlings hatch. Young disperse to nearby corners and mature over a few months. Because conditions indoors stay stable, overlapping generations can build a persistent population in an undisturbed basement or garage.
Habitat & Behaviour
Cellar spiders favour dark, damp, undisturbed spaces: basements, crawl spaces, garages, cellars, and the upper corners of ceilings in cool rooms. They build loose, messy webs — not sticky orbs — and hang inverted, waiting. The signature defensive whirl when touched or threatened is a reliable field mark. They readily add to and abandon webs, which is why old cellar-spider webbing accumulates into the dusty grey tangles common in neglected corners.
Diet
Cellar spiders eat insects that wander into their webs — and, notably, other spiders. They’re known to leave their own web to invade a neighbouring spider’s web, throw silk over the resident, and kill it, including species larger than themselves — even a wandering wolf spider that strays too close. This predatory habit makes them a natural check on other basement spiders, part of why arachnologists consider them beneficial rather than a pest.
Signs of Infestation
- Loose, irregular webs in ceiling corners of basements, garages, and crawl spaces — the most common sign.
- Pale, long-legged spiders hanging upside down that whirl when disturbed.
- Accumulating dusty grey webbing where old and new webs pile up over time.
- Females carrying a ball of eggs in their jaws, visible on close inspection.
Damage Caused
None. Cellar spiders cause no structural or material damage. The only real consequence is aesthetic: the loose, dust-collecting webbing they leave in corners and ceilings makes basements, garages, and storage areas look neglected.
Health Risks
Effectively none — and this is where the myth needs correcting. The claim that daddy long-legs have the world’s deadliest venom but can’t bite is an urban legend with no basis in fact. Research shows pholcid venom is unusually weak even against insects, the spiders can and do bite their prey, and there is no hidden potency. Bites on humans are essentially unheard of and would be trivial. Cellar spiders present no health risk to people or pets.
Seasonal Activity in Ontario
Unlike outdoor spiders, cellar spiders are active year-round indoors, sustained by the stable warmth of heated Ontario basements. You’ll notice them in any season, though numbers can climb through summer when humidity and insect prey rise and more food enters the lower levels of the home. Damp basements in Whitby, Oshawa, and across the GTA are prime year-round habitat.
Where They Hide
Ceiling and wall corners of basements, crawl spaces, cellars, garages, and cool storage rooms; behind and beneath stored items; and in undisturbed nooks where webs won’t be swept. They favour the coolest, dampest, least-trafficked parts of a home.
How They Enter Homes
Cellar spiders establish indoors and largely stay there, but new arrivals come through foundation cracks, basement window gaps, garage thresholds, and utility penetrations, and ride in on boxes and stored items moved from garage to basement. Once inside a suitable damp space, they breed in place — so an established population is homegrown rather than a steady invasion from outside.
Prevention Tips
- Vacuum webs, spiders, and egg clutches regularly — a hose attachment clears everything at once.
- Run a dehumidifier in the basement; aim for humidity below 50% to make the space less hospitable.
- Fix leaks and damp spots that support the insect prey cellar spiders feed on.
- Seal foundation cracks, basement window gaps, and utility penetrations.
- Declutter storage areas so there are fewer undisturbed corners to colonize.
- De-web consistently — persistent removal discourages rebuilding in the same corners.
The web-removal and prevention guide covers the vacuum-over-broom method in more detail.
DIY vs. Professional Treatment
For most homes, cellar spiders are a DIY matter — vacuum the webs, drop the humidity, and they thin out. Professional treatment enters the picture when a basement or crawl space has a heavy, persistent population that keeps rebuilding, usually because chronic dampness and an insect food supply are feeding it. In that case, treating the harbourage and the underlying insect prey — not just the visible webs — is what resolves it, the same broad approach used for residential spider control generally. Sani IQ’s spider control service backs its work with a Pest-Free-Or-It’s-Free guarantee; see the 2026 cost guide for pricing.
References
- Burke Museum — Daddy-longlegs Myth
- UC Riverside — Daddy Long Legs
- Royal Ontario Museum — Spiders in Our Backyard
Last updated: July 16, 2026 · Reviewed by Sani IQ licensed technicians