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Vampire flies feast on the backs of cattle

News editor

Hidden within the image of cattle grazing peacefully in the rolling green pastures of the Flint Hills is a blood feast.

The tiny vampires look like ordinary houseflies, but horn flies, armed by evolution with piercing mouthpieces, ride the backs and bellies of cattle, dining on the blood of their bovine benefactors 10 to 20 times a day.

In small numbers, they’re a painful annoyance. But a colony of 100 horn flies on one cow can inflict between 30,000 and 60,000 blood-sucking bites in a month.

“They’re spending as much time fighting flies as they are grazing,” Marion rancher Nick Kraus said.

Horn flies aren’t the only ones that can plague cattle.

Face flies, as their name suggests, live off secretions from a cow’s eyes and nose. They don’t bite, but will take advantage of an oozing wound.

Stable flies are another bloodsucking variety, attacking cattle’s legs.

Together, they pose health risks, disrupting grazing patterns, transmitting pink eye, and potentially causing anemia, all of which compromises weight gain. University of Arkansas researchers found calves feeding on cows with 100 horn flies were, on average, 17 pounds lighter at weaning.

“It’s difficult to see performance loss,” Marion veterinarian Brendan Kraus said. Nick and Brendan are brothers.

“We’ve had terrible problems with pink eye, everybody has,” Nick said. “Bad eyes will affect their weight gain, too.”

Nick has attacked horn flies from the inside out, using insect growth regulators in mineral feed supplements, he said. The regulators permeate cattle feces, which is where horn flies breed.

“They lay eggs and they hatch, but the larvae don’t grow,” Nick said. “It’s critical if you can get rid of those first couple of generations of flies.”

“Those can do some good,” Brendan said.

Ear tags infused with insecticides can be effective for both horn and face flies, Brendan said. The tags can also be effective reducing ticks.

One method to apply insecticide directly to cattle hides in the use of a back rubber, Brendan said.

“Sometimes it will be on the mineral feeder, or something else they walk underneath,” he said. “They’ll walk under it a few times and discover they’ll have less flies on their backs.”

“I’ve used some before, and I have some mops that go on mineral feeders for face flies,” Nick said. “We’ll put like an insecticide with a mineral oil mix on them”

The back rubbers are particularly effective when cattle are in more controlled spaces. Once they’re released into the fields for grazing, additional tactics are used.

“One of the challenges is making them last long enough to get through the grass season,” Brendan said. “The typical treatment time is right before they go to grass.”

If cattle on pasture have persistent fly problems, Brendan said some ranchers will try to corral them and use a large sprayer to apply insecticides.

A relatively new addition to the range-based arsenal lets ranchers take direct aim against flies on individual cows.

“It basically looks like a paint ball gun,” Brendan said. “It shoots them with a ball with insecticide.”

Evaluating the effectiveness of different treatments can be difficult, Nick said, because yields are affected by many factors and change from year to year.

“Some guy will use a new product and have the biggest calves he’s ever had,” Nick said. “You don’t know. You don’t want to try three new things in one year, because then you can’t know.”

The Kraus brothers agreed the primary goal in fly management isn’t to completely eliminate flies, but to keep the populations below the point they have a negative impact.

“You just tolerate it sometimes,” Nick said.

Last modified May 7, 2015

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