There are ten species of blowflies, two of which are attracted to bluebird nests, and are most virulent in eastern bluebird boxes. Blowflies, like many other insects. give off special scents, called pheromones. Large screened openings at the nest level were made. The concentration of blowflies and wasps proved to be not significantly changed. Darling and coworkers also found that bluebird nests constructed of pine needles had no blowflies.
More research needs to be done.
In answer to a question about whether old nests should be thrown out in the fall, Chris Darling advised that nests should be thrown out deep in the woods. rather than on the ground near the box. This procedure makes it more likely the parasitic wasp eggs which may be in the nest will survive the winter. When the nest is left in the box, the wasp eggs and larvae probably would not survive. Use of chemicals such as Flys Away II were not considered in the above study.