The prey chain: why lights concentrate spiders
Spiders don't go to lights. Insects do. The chain is: outdoor lights attract flying insects at night — moths, gnats, midges, crane flies, small moths, and in summer, mosquitoes. These insects concentrate around light sources because of phototaxis — they navigate by light, and artificial light disrupts their navigation systems. Spiders, which don't fly and aren't phototaxic, learn through experience that web locations near light sources produce more prey catches than locations without lights. Over the course of a season, web-building spiders migrate their positions toward lights. This is classical conditioned learning in an invertebrate — spiders reinforce behaviours that produce food rewards.
In Metro Vancouver, this effect is most pronounced in late summer and fall. A porch light that has been on all summer has been conditioning the local spider population for months. By September, the corner of your porch light fixture and the adjacent soffit have consistently produced prey throughout the summer, and the spiders around the property reflect that. The fall migration of male house spiders is happening simultaneously, and the lit areas near entry points produce an unfortunate confluence: spider-concentration near the building at exactly the time when male spiders are trying to get inside.
The light spectrum problem
Not all light spectra attract insects equally. Short-wavelength light (blue, UV, white) attracts many more insects than long-wavelength light (yellow, orange, red). Traditional incandescent bulbs emit a broad spectrum including significant UV, making them high-insect-attractants. White LED bulbs, particularly cool-white (5000–6500K), emit significantly more blue-spectrum light than incandescent and are potent insect attractants. Warm-white LED (2700–3000K) emits much less blue spectrum and attracts substantially fewer flying insects. True yellow LED bulbs (around 2200K) are the lowest insect-attractants in common commercial use.
| Light type | Colour temperature | Relative insect attraction | Spider concentration effect |
|---|---|---|---|
| Traditional incandescent | ~2700K but with UV component | High | High — legacy standard problem |
| Cool white LED | 5000-6500K | Very high | Very high — worse than incandescent |
| Neutral white LED | 3500-4000K | Moderate-high | Moderate-high |
| Warm white LED | 2700-3000K | Moderate | Moderate — recommended minimum |
| Yellow LED (2200K) | ~2200K | Low | Low — best single-bulb option |
| Motion-activated (any spectrum) | Varies | Low on average | Low — reduced cumulative exposure |
| Motion-activated yellow LED | ~2200K | Very low | Very low — optimal combination |
Practical lighting changes
- Replace all exterior porch lights, soffit lights, and security lights with warm-white (2700K) or yellow-spectrum LED bulbs. This is the single highest-impact change — it reduces insect attraction throughout the season, not just near the migration window.
- Add motion sensors to lights that have been on all night. Motion-activated lights reduce cumulative insect-attractant hours dramatically. A light on for 2 hours instead of 8 hours produces roughly 75% less insect attraction over the summer.
- Reposition flood lights and security lights away from the building wall and foundation. A light mounted 3 metres from the building illuminating the driveway attracts insects away from entry points. A light mounted above the door concentrates insects directly at the entry.
- Cover interior lighting near windows during peak spider season (August–October). The light from an interior lamp visible through a window attracts insects to the window surface from outside — and spiders follow. Closing blinds or curtains in the evening reduces this effect.
- Consider solar-powered motion-activated garden lights for perimeter paths — these activate briefly for foot traffic and have no sustained insect-attractant effect.
The web removal + lighting change combination
Changing lighting alone doesn't remove the existing spider webs that have built up over the season. The most effective approach combines the lighting change with a thorough web removal sweep: remove all visible webs and egg sacs at the same time you switch to the new bulbs. This resets the baseline. Over the following weeks, the reduced insect attraction means fewer prey catches for any newly-positioned webs, which means fewer reinforcing signals for spiders to concentrate near those light locations. Combined with a pre-migration perimeter treatment in late July, this produces significantly lower fall spider concentration at entry points compared to lighting alone or treatment alone.