There may be a colony right behind your drywall.

Wasps hovering around your house, even after you've knocked down every nest. If they keep coming back, they're not rebuilding from outside. They're coming from inside your walls. 

Spiders crawling through the baseboards are a sign that pests are already living in the walls. They're not just passing through. They're using your weep holes as a front door. 

Rats inside or around your home with no nest in sight. If you can't find where they're coming from, they're likely nesting inside the walls. 

A draft or cold spot near your walls means the insulation is being disturbed. Pests chew through it to build their nests, and the damage lets air through. 

Ants trailing along the foundation are following a path that leads somewhere. If that path leads to a weep hole, they're already inside. 

Mice you can hear scratching but can't find the entry point for. They're in the walls, and they got there through the weep holes.