Carpenter bees chew nice round holes in soft, weathered wood. Some solitary bees and wasps even create brood-rearing tunnels in soft mortar between bricks. These seem mundane after seeing the handiwork or an unknown bright green wasp or bee that has chewed two sets of three holes approximately 18 inches apart in a plastic window frame. Not only does the hard surface of the plastic seem to defy insect attack, and the smooth surface would hardly be expected to provide a place to land and start a hole.
A number of other insects will take advantage of openings in structures and buildings. Grass-carrying wasps (Figure 2) that select tracks of seldom-used sliding glass doors (Figure 3) to pack with grass and provisions (such as the grasshoppers that they collect and bring “home” as food for their larvae). Their efforts usually remain unnoticed until fall cleaning.
This mason bee is using an opening in a door threshold to gain access to a void that provides a protected brood chamber. Use of an insecticide dust followed by plug that allows drainage is the best way to deal with them. This is very different from honey bees or wasps that may nest in wall voids or attics. (Video: M. Klahr, Boone County)
By Lee Townsend, Extension Entomologist