Question: “We have a lot of wasps in our structure in the Fall and in the Spring. We can’t locate any nests at all. Where are they coming from?!!!!”
Answer: This is a common problem, especially in cooler climates where wasps and other insects must overwinter. In these cooler climates, the wasp society starts to break apart in the Fall. The workers stop caring for young, the queen stops laying eggs, and a large number of new queens and fertile males are then produced from the final batch of larvae in the nest. The male and female mate, and the male dies. The newly inseminated females are the future queens of next years nests. These females will start foraging for a place to spend the winter. It may take several days for her to find a suitable place. During this time she will buzz around surfaces, cracks and crevices in search of a suitable place to overwinter. Once she finds a suitable place, she will move in and wait out the winter.
During this time, wasps may “awaken” on warmer days and work their way into the building (instead of out). As a result, they often end up inside structural spaces where people may encounter them.
So, what can you do? Well, exclusion would be best. If you can build them out, it will prevent the problem for years to come. In commercial and residential structures, treating the exterior as mentioned above may provide some relief. If you can make surface applications in non-living areas such as attics, you may get results if the wasp forages across these surfaces. In commercial structures, a surface treatment may be accomplished to the walls above a suspended ceiling for instance.