The ecological math: what BC garden spiders actually eat
A single garden spider consumes between 2,000 and 8,000 prey insects per year, depending on species and web placement. In a Metro Vancouver garden, those prey insects are overwhelmingly pest species. Cross orb-weavers (Araneus diadematus) — the large autumn web-spinners that stretch across your patio furniture — catch mostly flying insects. Mosquitoes, fruit flies, gnats, whiteflies, leafhoppers, and small moths are well-documented prey. A cross orb-weaver running a well-positioned web catches between 30 and 80 insects per night during peak season.
Jumping spiders (Salticidae) are daytime hunters that actively stalk aphid colonies on rose stems and vegetable plants. Several jumping spider species in BC are recorded aphid predators. Wolf spiders, which move through soil and mulch, eat ground-dwelling pests including slugs (small ones), earwigs, root weevil larvae, and a range of small flies. Crab spiders (Thomisidae) hide in flower heads and catch pollinators alongside pest insects, but their net effect on pollinator populations is small relative to their aphid and pest fly control.
| Species | Hunting method | Primary prey | Garden benefit |
|---|---|---|---|
| Cross orb-weaver (Araneus diadematus) | Aerial web | Flying insects — mosquitoes, gnats, moths | High — active August–October |
| Jumping spider (Salticidae spp.) | Active stalk | Aphids, small flies, leafhoppers | High year-round |
| Wolf spider (Lycosidae spp.) | Ground hunt | Earwigs, ground beetles, sluglets | Moderate — soil pest control |
| Crab spider (Thomisidae spp.) | Ambush in flowers | Flying insects, bees, aphids | Moderate — flower pest control |
| Orb weaver (Argiope, Larinioides) | Aerial web | Large flying insects, wasps | Moderate — summer-fall |
| Sheet web spider (Linyphiidae) | Sheet web at ground | Aphids, springtails, thrips | Moderate — low vegetation pests |
The treatment trade-off: what you lose when you spray
Pyrethroid perimeter treatment around the exterior of your home — the standard spider control application — kills not only target spiders but also beneficial spiders in the treated zone. The residual period (60–90 days) suppresses the spider population at the building perimeter for that window. In a normal year, this covers the late-summer peak migration period, which is the management goal. The trade-off is acceptable because the treatment zone is narrow (the foundation perimeter and immediate building exterior).
What causes ecological problems is whole-yard application. Broadcasting pyrethroid through a garden eliminates the spider population across the treated area. The prey insects that spiders were controlling — aphids, gnats, whiteflies — aren't as sensitive to pyrethroids as spiders are. Aphids are plant-contact insects; they're somewhat protected by the plant surface. Flying insects can recolonise from outside the treated zone within days. The spider population takes weeks to months to recover. The net result: pest pressure rebounds to a higher level than before treatment within 60 days. This is the classic pesticide treadmill dynamic, and we see it specifically in accounts that have had whole-yard spider sprays from previous pest control companies.
Species you want in your BC garden
Cross orb-weavers deserve special mention because they're the most visible and most commonly disturbed garden spiders in Metro Vancouver. They build their large, elaborate spiral webs across open spaces — between shrubs, across patios, between fence posts. In fall, when they're fully grown, females can reach 15 mm with the abdomen, and the webs span 30–60 cm. Homeowners frequently walk into them or pull them down deliberately. Both are understandable responses, but it's worth knowing that a single orb-weaver in a well-placed web catches more mosquitoes per night than a citronella candle prevents.
Jumping spiders are the other species that warrants active appreciation. They're small (5–10 mm), distinctively patterned, and have eight large eyes that give them remarkable visual resolution for their size. Several species are common on Metro Vancouver fences, exterior walls, and window frames. They're diurnal hunters — you'll see them actively stalking prey in daylight. They're curious animals that will turn to face you if approached, and they're completely harmless. A jumping spider hunting aphids on your vegetable plants is doing exactly the pest control work you want happening.
When garden spider management is actually warranted
- Egg sacs in window frames, door jambs, or exterior light fixtures — these are entry vectors. Remove and treat harborages at structural openings while leaving garden spiders intact.
- Heavy webbing on patio furniture or pathways that are walked through daily — minor and easily remedied with a bamboo web-clearing wand, doesn't require treatment.
- Spider phobia preventing yard use — a legitimate quality-of-life concern. Targeted treatment of patio and seating areas while leaving vegetable beds untreated is a reasonable compromise.
- Medically significant species in children's play areas — western black widows near play structures warrant treatment regardless of the ecological argument.
- Commercial food-production properties — some food safety standards require spider-free processing environments; this is a compliance issue that overrides the ecological argument.