About Parasites found in Mountain Bluebird Nest Boxes

By Steven Shumborski

The fly larvae that feed on the young bluebirds are common flies. I collected a number of the larvae and pupae from bluebird nest boxes this summer and put them in a jar.

Then I left them for a couple weeks until the adults emerged from their cocoons, and what came out? Common flies, nothing special, just the everyday flies you see everywhere in fields and around cattle.

What can I put on the floor of the nest box under the nest to kill the larvae?

The fly larvae can be removed from drop down floor nest boxes by opening the floor of the nest box. Check the floor for fly larvae after the bluebirds have hatched, usually seven days after hatching, and again a week later if possible.

Remove the pin holding the floor, lower the floor slightly, catch any larvae that fall out of the box in a shovel, and then gently rub the bottom of the nest to dislodge any larvae that are in the nest material. Then close the floor.

Use caution when opening the floor. Some nests have very little grass under the chicks and they can fall through the nest material onto your shovel. Weekly checking is ideal as the flies develop quickly. When there are 30 to 50 larvae in the nest, the bluebirds are often killed by the fly larvae.