The biology behind the October surge
House spiders build funnel webs in sheltered corners — typically behind furniture, along baseboards, in basement corners, and in window recesses. Female house spiders stay in their webs year-round. Males, however, mature in late summer and begin a mating dispersal phase. They leave their webs, move through available spaces (including building interiors), and search for female webs to approach. Multiple males may be moving simultaneously through a household in October, producing the impression of a sudden spider influx. The females, who were present all year, become more visible because the male activity drives them out from behind their webs.
BC spider species you will encounter in fall
- Giant house spider (Eratigena atrica): the large brown spider seen crossing floors in October. Leg span up to 80mm. Harmless — no medically significant venom. Beneficial predator of household insects. The 'scary' September/October spider in Metro Vancouver homes.
- Common house spider (Tegenaria domestica): smaller relative of the giant house spider; more often found in basement corners and crawlspaces. Builds messy funnel webs.
- Cellar spider (Pholcus phalangioides): long thin legs, found in basement ceiling corners and under stairs. Does not participate in fall dispersal pattern; present year-round.
- Zebra jumper (Salticus scenicus): small black and white jumping spider; more common in summer than fall.
- Hobo spider (Eratigena agrestis): formerly considered medically significant; current research does not support a venom-mediated tissue damage claim. Behaviorally similar to giant house spider.
The connection between fall spiders and other pest entry
Spiders enter through the same gaps that mice, earwigs, and other fall pests use. A surge in indoor spiders in October is, among other things, a structural entry-point indicator. If male house spiders are moving through your home freely, there are enough structural gaps at ground and basement level that the exclusion work done in October for rodents also addresses the spider access problem. The two problems share the same solution.
Reducing fall spider pressure: what works
- Complete fall exclusion work on all ground-level and basement entry points — sealing for rodents seals for spiders.
- Reduce exterior lighting or switch to amber/yellow bulbs — white light attracts the flying insects that spiders eat, concentrating spider food sources and spiders themselves near entry points.
- Remove ivy, dense ground cover, and wood piles immediately adjacent to the structure — ground cover within 1m of the foundation provides shelter and food web for spiders.
- Vacuum webs from basement corners and behind furniture monthly through October — removing webs without chemical treatment and releasing spiders outdoors is the most proportionate response.
- Sticky traps on the basement floor confirm the volume of spider movement and can help identify primary entry routes.
| Situation | Response |
|---|---|
| 1–3 large house spiders per week in October | Normal fall dispersal — relocate outdoors |
| Consistent spiders through November and beyond | Entry point issue — book exclusion assessment |
| Web clusters in basement corners | Normal house spider presence — vacuum webs periodically |
| Very small spiders near potted plants | Fungus gnats or soil mites food source — check plant drainage |
| Black spider with red hourglass mark on abdomen | Potential black widow — do not handle, call professional |