House Wrens are small but feisty. Every bit as high energy as the busiest warbler, they bustle about the bushes scaring up food, and scaring off potential competitors. Put out a bluebird box, and you are just as likely to wind up with a house wren in there instead. In fact, these little tyrants will kick out the eggs and even young of other species just to take over the nest box. Then they stuff the box full of sticks all the way up to the entrance hole to prevent anything else from getting in.
Young birds in nest boxes or tree cavities are susceptible to parasitic mites and flies; in fact, heavy parasite infestations can sap baby bird growth so much they fail to mature. But house wrens have a strategy for dealing with this: they capture egg sacs of spiders and import them to the nest box to feed on the parasites. Problem solved.
Their aggressive behavior and adaptability to a variety of habitats and climates has enabled house wrens to become one of the most widespread species in the western hemisphere. It is a permanent resident throughout South America and can be found breeding from Canada south through the West Indies and Central America. The mighty mite is a big success.