"Waiting to Attack"...

A likely immature, female yellow fly sits in waiting for movement.
Identification between the species of Yellow, Deer and Horse flies is daunting. There are many variances in size, body color, hair, wing markings, antenna length, eye separation (females have a larger space between the eyes, etc. For example, there are over 250 species of deer and horse flies.

Horse flies (Tabanus), about 1/2" to 1.25" in length, often have dark bodies and darkly colored wings. Yellow/Deer flies (Chrysops), which are often smaller, about 1/4" in length - about the size of a house fly, have transparent wings dark lines or bands.

While they are similar looking, they do have differences. Deer fly, for example, has wings that are A-shaped whereas horse flies have wings that fold straight back when at rest. Horse flies also tend to be slightly larger with bigger eyes and a slightly wider body.

The yellow fly is a fierce biter. Like mosquitoes, it is the female fly that is responsible for inflicting a bite. The males are mainly pollen and nectar feeders. Tabanids lie in wait in shady areas under bushes and trees for a host to happen by. Sight is the main host finding mechanism, but carbon dioxide and odor also play a role. Moving objects, especially if dark colored, are most prone to attack.

Deet (diethyl toluamide) and citronella are the more effective repellents.

Photo # K01_1330.
(c) Kelly Shipp Photography