Name: Chrysops spp.

Deer fly

Deer fly

Alias: The deer fly. There are multiple species of deer fly throughout the world, but they share many characteristics. The deer fly almost looks like a smaller version to the horse fly, approximately 5-10 mm long. It has large colorful eyes, a pointed scissor-like mouth, and its striped wings give it an overall triangle shape. They can vary in color from grey, brown or black. They seek out their prey by following carbon dioxide trails exhaled by their unsuspecting victims. Eggs are laid in wet conditions and larvae survive in aquatic habitats. They pupate in late spring as ponds dry up. Mating occurs in early summer, which is when the females begin their hunt.

Crimes: Females must feed on blood to produce the next generation. They use their scissor-like mouth parts to cut into their prey, which is usually made up of larger vertebrates such as deer, elk, livestock and even humans.

Redeeming qualities: None.

Sentence: Natural predators are the No. 1 cause of death for deer flies. The reason they prefer large vertebrates is because they can usually obtain large quantities of blood from areas that are difficult to reach, such as the upper back or underbelly. Smaller creatures can pick them off easily. They are prey to birds, rodents, and various parasitoid wasps. Nature controls their populations quite well, and the real task is to manage them on an individual level. Bug sprays with DEET are great as dissuading them from biting. Pyrethroid based fly sprays for horses and livestock are also very effective. Remember to read the label instructions when using and pesticide.

For more information on dangerous and beneficial bugs, call UI Extension educator Joseph Sagers at 208-745-6685 or email