Overview
The cellar spider (Pholcus phalangioides), also called the daddy long-legs spider, is the most common spider in Montreal basements and crawl spaces. It is completely harmless to humans — its fangs are too small to penetrate human skin — and is actually beneficial, feeding on other insects including mosquitoes, flies, and even other spiders. However, its loose, irregular webs in corners and along walls are a common nuisance complaint.
How to Identify Cellar Spiders
- Body size: 6–9 mm (small)
- Leg span: Up to 7 cm — the very long, thin legs are the most distinctive feature
- Colour: Pale grey or tan body with darker markings
- Web: Loose, irregular, three-dimensional web — not the classic orb web
- Behaviour: Vibrates rapidly in its web when disturbed — a defensive behaviour
- Habitat: Dark, humid spaces — basements, crawl spaces, garages, and corners of rooms
- Activity: Year-round indoors; most visible in late summer and fall
Biology
- Lifespan: 1–3 years
- Egg sacs: Female carries egg sac in her chelicerae (mouthparts) until eggs hatch
- Eggs per sac: 20–30
- Diet: Insects, other spiders, and occasionally other cellar spiders
- Hunting method: Passive — waits in web for prey to become entangled
- Preferred conditions: Humid (above 60% relative humidity), dark, undisturbed spaces
- Seasonal pattern: Populations peak in late summer and fall as they seek indoor shelter
Risks
- No health risk: Cellar spiders are completely harmless to humans — their fangs cannot penetrate human skin
- Beneficial: They feed on other insects, including mosquitoes, flies, and other spiders
- Nuisance: Webs in corners and along walls are the primary complaint
- Myth: The "daddy long-legs is the most venomous spider" myth is false — cellar spiders have very mild venom and cannot bite humans
Signs of Presence
- Loose, irregular webs in corners, along walls, and in ceiling angles
- The spider itself — long-legged, pale, hanging in its web
- Egg sacs: Small, round, loosely wrapped in silk — carried by the female
- Shed skins: Translucent exoskeletons near the web
- Concentration in basements, crawl spaces, and garages
Prevention
- Reduce basement humidity with a dehumidifier — target 40–50% relative humidity
- Remove webs regularly with a vacuum — this also removes egg sacs
- Seal entry points: gaps around windows, doors, and utility penetrations
- Reduce outdoor lighting near the house — lights attract the insects that spiders eat
- Keep basements and storage areas organized and clutter-free
- Address underlying insect problems — spiders follow their food source
Professional Treatment
Cellar spiders rarely require professional treatment. Regular web removal with a vacuum (including egg sacs) and humidity reduction are usually sufficient. If spider populations are very high despite prevention efforts, this often indicates an underlying insect infestation that is attracting them. Professional spider treatment includes exterior perimeter spray, interior crack-and-crevice treatment, and web removal.