Spider populations generally track insect populations because insects are their food source. Mulch, vegetation and irrigation around the structure provide the ideal environment. Applying boric acid granular perimeter bait will not kill spiders directly, since they don’t eat bait, but will work indirectly in two ways:
- It reduces the population of their insect food source.
- Insects dying from boric acid become slow-moving prey. Spiders that eat these insects will ingest the boric acid as well, because the active boron is a mineral and doesn’t break down once ingested by an insect.
A botanical wettable dust or a micro-encapsulated pyrethroid applied to eaves will repel spiders from these potential entry points, as well as kill the spiders that contact it. Both will be picked up easily by spiders because they stand up on the surface.
Indoors, amorphous silica dust is an ideal choice for long-lasting, nonrepellent protection. Botanical wettable dust can be applied to boathouses and boat docks without water setback, as either a liquid, or as a dust applied to a cobweb brush and brushed into corners and edges.