There are lots of spiders in the Bay Area, including here in SF. But definitely fewer of other insects compared to other places I've lived.
I think it is partially the cool weather that slows them down and the long dry season. It seems especially hard on the typical flying insects that tend to annoy people. Most of the insect life I've seen prefers to root around deep in the topsoil where it is presumably warmer and not as dry.
Western Europe is similar. Coming from New England it blew my mind they barely even know what insect screens are in France/Germany/Switzerland. Just an unbelievable lack of insects compared to the eastern US.
Spiders and Argentine ants. Those are the only insects I consistently see in SF. Nothing in comparison to the Southeast though... I do not miss the mosquitoes and roaches.
I think it is partially the cool weather that slows them down and the long dry season. It seems especially hard on the typical flying insects that tend to annoy people. Most of the insect life I've seen prefers to root around deep in the topsoil where it is presumably warmer and not as dry.