Have you noticed strands of dry grass protruding from your window frame, sliding door tracks, or other narrow crevices around the home? Have you slid open your sliding screen and found debris lining the tracks? If so, you may have been visited by the GRASS-CARRYING WASP (Isodontia spp.), also colloquially known as a window wasp. But don't worry, these solitary wasps are good neighbors.
Grass-carrying wasps are beneficial solitary wasps that rarely (if ever) sting. Unlike bald-faced hornets, paper wasps or other social wasp, they do not create a large hive or nest. They do not have hundreds of daughters which defend the hive. Instead, a single female is working solo to find a protected crevice or tunnel to create a nest with a comfortable grass bed for her offspring. Window wells just happen to have those ideal characteristics that attract the wasps when its time to lay eggs. They may also be drawn to window weep holes, gaps beneath siding, hollow plant stems, nail holes, abandon tunnels from carpenter bees or beetles in dead trees or exposed wood, and other pre-existing holes and narrow cracks and crevices. If you have a "bee hotel" for mason bees and leafcutter bees, the grass-carrying wasp will also make use of those tubes and tunnels.
After finding a suitable site, the female begins to collect grass blades which she carries with her legs under her abdomen while she flies. You may spot the unusual site of a wasp flying through the air dragging large long blades of grass, often several body-lengths longer than she is. She will stuff that grass into the cavity to create individual nest cells where she will lay an egg along with some food for the larva. What kind of food? Paralyzed crickets!
Grass-carrying wasps hunt down tree crickets, young katydids, and other orthopterans. They use their stinger to paralyze the cricket so that it remains alive and fresh, but incapacitated. She will carry these prey back to the cavity and stuff several into the grass cell and lay an egg. When the egg hatches, the larva will begin to consume the paralyzed prey. The larva will spin a cocoon to pupate. Adults emerge in early summer to mate and begin the process again.
These wasps are not a concern and management is not required. Window wells can be cleared of the contents if they are unsightly or cause issues in opening doors and windows.
