Mason bee houses are easy to find these days but most are poorly designed death traps. Please don't buy them. pic.twitter.com/k6auUsFDu3— Colin Purrington (@colinpurrington) May 3, 2019
Many species of bees have suffered falling populations in recent years, due to environmental changes. People want to help them out by providing nests so that bees can produce offspring in safety, and commercial interests have stepped in to sell those nests. You can find bee houses in stores and online, but some are not really conducive to raising bee populations over time. Other nests are, but it's not a simple matter of hanging one and letting nature do its thing. Biologist Colin Purrington warns that even the best bee houses must be installed correctly and maintained to help bees thrive.
Regular bee care, Purrington said, involves storing the larvae-filled nests that the bees make inside the bee houses safely for the winter, cleaning and sanitizing the nests after the larvae have grown and left in the spring, and cycling out those breathable woods and paper straws regularly to make sure they’re not harboring parasites or bacteria. He also said it’s a good idea to cover the houses with metal netting to keep the birds out, as woodpeckers and bluejays find bee houses to be great restaurants.
A post at Earther explains the worst that can happen to bee houses, and has recommendations and links for proper backyard bee care.