Deer Flies Don’t Suck – They Bite

Dear flies don’t suck — they bite. Mosquitoes suck the blood from you. A horsefly uses a specialized mouthpiece to bite you and then feed on your blood. The entire biting process is more like a violent crime than a bite. A flea bites you, and a horsefly practically mugs you. Here’s how the biting process works with horseflies.

The Daggers of Doom

Horseflies have mouths that contain solid bone-like structures. Those are the mandibles and the labrum. The mandibles come together to form what appears to be two daggers side by side with the sharp edge facing outward. The combined point stabs deeply into the flesh, and once it hits a sufficient depth, the mandibles swing outwards. During that outward swing, the mandibles slice through flesh, vein, and capillary. Under magnification, you begin to see just how efficient the mandible of the horsefly is. There are tiny teeth along the cutting edge. Those teeth not only help the solid structure puncture the skin and muscle, but they also create a ragged edge which produces more blood.

The Labrum — A Tool of Efficiency

The Labrum is also a firm fixture of the horsefly mouth. It is wide and narrow and offers a design that mimics the shape of the mandibles when they are closed. It slides into the puncture that the mandibles make and there it begins to harvest the spewing blood. The center of the labrum is hollow. It contains the salivary duct, which floods the puncture wound with fly saliva. The saliva is an anticoagulant which keeps your blood from clotting. So in conjunction with those saw teeth on the mandibles, the saliva helps the blood to keep flowing. It is that chemical bath inside your flesh that causes the most pain. It is a nerve reaction. Your blood is sucked up the salivary duct by a structure that acts as a syringe.

The Queens of Efficiency

It is only the female horseflies that bite. The males are not capable of biting, and they have no interest in drinking blood. They dine on plant sap. This is an interesting fact because the different sexes do not compete for food sources. The female needs the protein in the blood to lay eggs. The males in the insect world are self-sacrificing because when a healthy female can lay more eggs, then more of the male’s DNA makes it into the next generation. Just ask the male mantid about the role of self-sacrificing males.

The female horse flies are so skilled at snatching a blood meal that the entire process happens before you can react. In short, not only do you get punctured, she drinks your blood and is gone before you can slap yourself.
Horseflies are violent in their approach to obtaining blood. People have tried to use pesticides on them for generations. Pesticides have little effect. What works is a tool that mimics large mammals as those are the prey of the horsefly female. The Fly Cage is one such tool. The females come in search of a meal and never fly out again.