These large insects provide a substantial meal to the hungry martin nestlings and are worth the martin's effort in capturing them. Dragonflies are swift fliers, but a colony of martins captures hundreds of them throughout the summer when feeding their young. Ironically, the dragonfly is one of the greatest predators of mosquitoes so, in effect, the more dragonflies that are captured by martins, the more mosquitoes that will live to bite another day. The energy expended in capturing a single large insect like a dragonfly is minimal compared with the energy it would require to capture the hundreds of mosquitoes that would equal the same amount of food as the single dragonfly. Therefore, it is in the martin's best interest for survival to target larger prey items than mosquitoes.
Martins are diurnal hunters, meaning that they hunt during the daylight hours.
Mosquitoes are mainly nocturnal, or nighttime hunters, meaning that they are usually just coming out to bite when the martins are coming in to roost for the night. Martins and mosquitoes seldom come into contact with each other. Martins feed quite high in the air and mosquitoes typically stay close to the ground. Martins, being strong fliers, typically hunt far away from their colony site. This means that all of the mosquitoes on your property where your martin housing is located are virtually untouched by your martins when they are away hunting.