Q: Wasps took up residence in my compost pile this year. I could avoid them for a while, but I’m hoping I can use the pile again next spring. How can I get them out of there?
A: Ground-nesting yellowjackets are probably the culprit here, and the good news is that they will disappear on their own by winter. In our area, social wasps like hornets, yellowjackets, and paper wasps don’t reuse the same nest for more than one year. By late autumn or early winter, the old queen, workers, males, and any juveniles that did not have time to mature will all die. Only mated young queens survive, leaving the nest of their birth to disperse and overwinter in a sheltered spot by themselves. They seek out insulated spots like hollows under fallen logs and nooks in stone walls, go into the insect version of hibernation, and emerge in spring as it warms up, each flying off to find her own site to start a new nest. She does all the nest-building and larvae-feeding work by herself until the first generation of young matures, so she has a limited ability to defend it from disturbance.
Nest remnants left in the compost pile will be abandoned (or will at least contain dead wasps) during winter, when you can safely dig it out for removal or just leave it to compost with the rest of the pile contents. Wild animals can also tear apart abandoned wasp nests, looking for easy-access morsels to snack on, though this presumably happens more regularly with visible above-ground nests.
Preventing a new generation of wasps from choosing the same appealing nest site in a future year might be challenging unless you enclose the pile in insect mesh or something to discourage queen wasps from exploring it in spring. Regular turning of the pile – recommended to keep it well-oxygenated anyway – might disturb a new queen too much to allow her to successfully begin a new nest.
By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun and Washington Gardener Magazine. Read more by Miri.
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