Bees and Wasps


I service a doctor’s office that is in a commercial building.  Over the past 2-3 years I have found European hornets nesting in the mulch near the entrance to the office.  I had little difficulty finding and treating nests and both the client and I were happy with the results after treatment.  However, this year the hornets are back and I can’t find any nesting sites for the life of me.  I have canvassed the surrounding area without any signs of nesting and have been unable to track any of the many hornets flying around the building.  Any ideas?

The good news is that European hornets are not aggressive and are (in most settings) beneficial due to their habit of preying on grasshoppers, flies, and other miscellaneous insects.  As you are well aware, the benefits of European hornets are not enough to overwhelm the face that large, stinging insects are not welcome in a place where people in various states of health are frequenting.  For a large number of these hornets to be present during the day time suggests that the nesting site is not far away.  Have you thoroughly investigated the building itself?

These hornets will nest in structural voids and their entrance may be inconspicuous.  If you have a stethoscope or other listening device, give that a shot.  Are there any trees in the vicinity with branches and leaves that would obscure views of a nest?

If you haven’t already, I recommend visiting the site at night to see if you can better observe their movements and track down the nest(s).  Focus your efforts on trees and perimeter walls and make sure to use a yellow filter on your flashlight so you don’t attract bees to your person.  If nest locating efforts continue to be fruitless, you can move on to secondary control strategies like treating for their food source and removing fallen fruit and other attractive organic matter.

I recently found dozens of tiny (what I believe to be) wasps in an interior wall near a window in a residence.  What could these be and why did so many of them appear at once when I’ve never encountered them before?

While ID is necessary to answer your question completely, the most likely explanation is that you stumbled across a bunch of parasitoid wasps.  Parasitoids develop inside of, and eventually kill their host.  Many wasp species fit the description of being a parasitoid, and all sorts of different organisms, like beetles, butterflies and moths, Hemipterans (true bugs), and even spiders, are used as hosts.  The female wasp oviposits into the egg or body of the host and the larvae develop inside the host until pupation, at which point the host is dead or close to it. Parasitoids are very specific in their host preference, which makes them great candidates for use in biological control.

There is/was some host species present in the structure that yielded all the wasps you found.  Unfortunately, identification of parasitoid wasps can be quite challenging, both due to their small stature and incredible species richness of the group.  Your best bet is to monitor throughout the structure for whatever the host might be, as the wasps you found were likely drawn to that area because of the light coming from the window.