The answer to 'when to treat for spider' is that the best time to treat for spiders in your home is in the fall, when spiders are actively seeking warm places to build their webs and lay their eggs. Spiders are most active during the cooler months as they search for food and shelter, so treating in the fall will help eliminate existing spiders and prevent future infestations.
It's important to treat for spiders before they have a chance to establish themselves and lay eggs in your home. Treating in the fall will disrupt their life cycle and prevent them from overwintering and multiplying in the spring. Regular pest control treatments throughout the year can also help keep spider populations in check and prevent them from becoming a nuisance in your home.