Southwestern Piedmont Master Naturalists: Altercation in a Nest Box

Altercation In a Nest Box: Eastern Bluebird vs. Bald-faced Hornet

By Christine Boran

In mid-April, I found a Bald-faced Hornet's nest (Dolichovespula maculata) hanging from the ceiling in nest box #32 on my 50-nest box Woolwine House Bluebird Trail in Patrick County. This nest was in progress by the queen hornet as she was creating the paper cylinder nest, the cells inside it to lay her eggs. She tends to those cells by feeding her larvae other insects in the cells to hatch later into worker hornets. No hornet eggs were yet laid yet inside the cells. We all know: once the workers are hatched, a hornet's nest can become dangerous for humans to be anywhere near it. Those worker hornets will defend the nest and their queen with a fury! No birds will use the nest box with an established hornets nest inside it. I decided to go back that night to scrape out the small nest in progress from the nest box ceiling with my paint scraper before the hornet nest became larger. When I returned at 9 PM to do this, I found a deceased bluebird in the nest box. It was dark, and even with my flashlight, I could not determine if the bluebird was male or female, but I did see a few added bluebird nesting materials on the nest box floor that took place after my daytime monitoring check. I left all as I saw it and returned in the morning to investigate this further in detail in daylight. What I found was indeed a deceased female bluebird, and next to her was the deceased queen bald-face hornet. I studied the deceased bluebird and found nothing visible to determine cause of death. I made a determination from the clues I had that the female bluebird may have tried to snap at the queen hornet inside the nest box to attempt to kill it (and possibly eat it). More than likely there was an altercation right then and there, and she was stung by the hornet. My thinking is the venom sting was too much for the bluebird to survive, and the queen hornet could not survive the physical injury from the bluebird. Though I’ve seen hornets try to use the inside of a nest box before on my 17-year old bluebird trail, I have never seen this where both bird and insect species had a duel inside the nest box and caused fatal injuries to each other. After removing the inactive cylinder hornet nest from the nest box, another pair of native cavity-nesting birds started to nest there on May 1 and fledged their young on June 18.

I support all native species, of course, as a Virginia Master Naturalist. Generally, I leave hornets nests as is as I find them on any of my outbuildings or on my house, if there is no risk to me or others; or in trees to allow them to reproduce. In my nest boxes, where I’ve had five native bird species attempt to reproduce inside them, I do not allow hornets or other wasp species to build their nest inside them during the birds’ nesting period (usually beginning of March through end of August). However, I do leave any mud-dauber “organ pipe” mud cylinders I find late in the summer attached to the nest box walls as is, after the birds have nested, so those wasp larvae can overwinter there.