Carrion beetles

We opened a bluebird nest box yesterday to find six dead chicks. They probably were four to five days from hatching. There was no way to determine why they died, but wet, cold weather could have been the cause. Such weather would prevent the parent birds from finding sufficient numbers of insects to keep the young birds alive. Bluebirds go from hatching to fledging (leaving the nest) in 14 days. Most songbirds fledge quickly. It takes a great deal of food to fuel that rapid development. Another possible cause of death would be blowfly larvae. This fly species lays its eggs in the nest. The larvae feed on the blood of the chicks, and can weaken them enough to kill them. The handsome fellow below and several like it ran off the dead birds and out of the box when it was opened. They're American Carrion Beetles (Necrophila Americana). They don't eat the flesh of dead animals. Instead, they eat the larvae of flies that lay eggs on the dead birds. The carrion beetles also lay eggs. The beetles eat the fly larvae to ensure that sufficient food is available when their eggs hatch. Part two of the story: The beetles carry mites that drop off when the beetles arrive at the nests. The mites eat fly eggs and larvae. This is a mutually beneficial arrangement: the non-flying mites remove beetle-larvae competitors at the site of the dead animal, and in return get carried by the beetles to their next meal. The carrion beetle is about half an inch long.