"We're very excited to get these birdhouses at all our rest areas, especially at no cost to the taxpayers," said Jim Carney, Missouri Department of Transportation state maintenance engineer. "Besides being graced with the natural beauty of the birds themselves, the more than 24 million travelers who stop at our rest areas will benefit from fewer flying insects at these sites."
Each purple martin, that inhabits Missouri from late April until late September before flying south, consumes several thousand flying insects each day, including mosquitoes. The bluebird, although not as prolific an eater, is the official bird of Missouri.
An interesting list of why people fail to attract purple martins appears here.