Two cows. Same University of Wyoming McGuire Ranch pasture northeast of Laramie near Sybille Canyon.
One cow has 383 horn flies sucking her blood; the other cow has four.
Why that remarkable difference?
Cody High School graduate turned veterinarian, turned Army major, and now a Ph.D. student at the University of Wyoming, Craig Calkins is helping UW Extension range specialist Derek Scasta unravel the mystery of a pestilence that costs the livestock industry billions of dollars in losses.
Calkins is eyeing whether shorter blood clotting times of individual animals clogs a fly’s attempts, whether a thicker hide frustrates flies, and if elevation and environmental conditions, such as colder and wetter areas, affect fly parasitism.
Considered a filth fly, horn flies (Haematobia irritans) feast on a cow’s blood, leave to lay their eggs in manure, then fly back to their beef buffet. Eggs hatch after about two weeks, and a new generation begins.
The flies pierce the hide and inject an anti-coagulant to help free the flow of blood. Cattle swing their heads, slap their tails and twitch their skin in attempts to stop the biting.