We’re approaching one of my favorite times of year. It’s bluebird season! We currently have five bluebird boxes on our property. Last year, one was filled with bluebirds and the others were claimed by wrens, swallows, and other cavity nesters.

Now, as a responsible home owner, it’s time to clean them all out. House Wrens typically clean out their own boxes, but bluebirds depend on the landlord to take care of it. That means us. And it’s critical that the box get cleaned before the birds arrive and start to move in. That means now!

I used to feel guilty about removing all those laboriously gathered twigs and dried grasses. The birds had worked so hard, it didn’t seem fair to just dump it all out. Then I read up on the number and variety of parasites that accumulate in a nest, and realized that I was really doing the birds a huge favor. Who wants to move into a bug-infested home, especially when you’re about to have babies?

First of all, there are the mites. Mites are really teeny tiny spiders (and if you don’t know how I feel about spiders, try typing “spider” into the search box at right). I definitely did not want spiders crawling on my hands, up my arms, inside my… yeah, you get the idea.

Feather mites (left) are the most common species you’ll likely have to deal with They aren’t likely to kill the birds, but they can certainly make life miserable. (The good news is that they don’t bother people. What a relief.) Unfortunately, there are other kinds of mites that feed on skin and blood, and a heavy infestation can kill the nestlings.

Then there are blowflies. Talk about disgusting! The adult flies come and lay eggs in the nest. When these hatch, the larvae (right) sneak up and attach themselves to the baby birds—and suck their blood. Eww. Enough larvae will severely weaken or kill the young birds. Warm, wet weather encourages these nasty insects.

Blackflies (aka buffalo gnats) are another insect that attacks birds in nests. They cut their way through the skin to feed on blood. The flies prefer areas with running water and much of Colorado is on the dry side, but in areas where they are found, they can kill the young birds through blood loss, infection, or even shock. If you have blackflies in your area, take measures to keep them out of the nest box. Screening ventilation holes may help, but of course they can fly right in the same door the birds use. Vanilla may mask the CO₂ that attracts them in the first place. Painting the outside of the box white sometimes helps. As a last resort, spray the outside of the box with a pyrethrin-based insecticide.

Ants and wasps are two more intruders that sometimes take shelter in a nest box, and can drive the parents away from their offspring. Ants can be deterred by spreading a sticky barrier such Tanglefoot or petroleum jelly around the base of the post or tree supporting the nest box. Wasp nests should be knocked down the moment you notice them.

You’d think the birds would just eat all these nasty bugs, but apparently these parasites are too good at hiding. For instance, the blowflies only come out at night, when the bug patrol is sound asleep. Sneaky.

Another reason to let the birds build a new, clean nest is the lack of plumbing in most birdhouses. Think about it. The babies can’t yet fly, yet they’re munching down an endless supply of birdy baby food. And they don’t wear diapers. Instead, they produce a compact bundle called a fecal pellet. The parents start out removing these pellets as they appear, flying them out the nest (and perhaps dropping them on an unsuspecting cat). But after week after week of this chore, they get a bit tired. House Wrens, for example, stop removing the pellets several days before their brood fledges. Maybe that’s one way to encourage the babies leave the nest!

Cleaning is simple. Open the box. Using gloves (after reading this list, who wouldn’t?), put your hand in a large plastic bag, then invert the bag over the nest. You can toss it in the trash or move it some distance away, then leave it for the good bugs that eat the bad bugs. Finally, sponge down the inside of the box with a 10% bleach solution.

There are many benefits to hosting nesting birds—they eat mosquitoes and other insects, they fill the air with bird song, and you can watch whole incredible process right at home. But if we’re going to invite them in, it’s our responsibility to make sure the neighborhood is safe. Cleaning out the nest boxes is a good start.
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Photo attribution:
Feather Mite: By Daktaridudu (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)%5D, via Wikimedia Commons
Blowfly larva: texashelp.tamu.edu/011-disaster-by-stage/recovery/ER-025-Controlling-Blow-Flies.php
Blackfly: Oklahoma State University, entoplp.okstate.edu/ddd/insects/blackflies.htm