The horntail wasps derive their name from the presence of a horn-like projection on the top of the last segment of the abdomen on the female. These are solitary wasps whose larvae feed within the sound wood of dead trees, gathering their nourishment from a fungus that grows with them as they bore through the wood. The female wasp will lay her eggs only on the bark of trees, injecting them below the surface. In this way it is common for lumber to be milled with the wasp larvae already in it, allowing the larvae then to be built into a structure. The wasps will not infest wood already in use. Once the adult wasp develops it bores its way out of the wood through whatever is in its way, creating pencil-sized round holes in sheetrock, paneling, wallpaper, or even tiles. The adults then go to lighted windows to attempt to escape. These wasps cannot sting or bite, but due to their large size and loud flight are greatly feared by occupants of the structure in which they emerge.
When these wasps are emerging from structural wood members it is best to allow it to run its course, and once all the wasps have emerged the holes can be repaired. There is little damage done, and normally the small number of wasps present do not warrant fumigation or other control measure. They will not reinfest.