Fly Geography as a Fly Defense
By Caitlin Richards
Not only are flies a nuisance to cattle, but they are a nuisance to the ranchers who are trying to control them. Even though all flies are bothersome, cattle may have a variety of species causing them trouble. It’s important for ranchers to take this into account because the most effective treatment options depend on the species.
“You are going to control the different species using different methods,” says Larry Hawkins, senior technical service veterinarian with Bayer Animal Health. “Different species breed in different areas and feed differently, as well.”
Luckily, producers can easily identify the fly species bothering their cattle. The location of the fly on the cattle can shed light on the species. The four primary species that are a pest for cattle are the house fly, stable fly, horn fly and face fly.
House fly
The house fly will most likely be the easiest species for producers to recognize. House flies are the flies buzzing around trashcans and being shooed away at family barbeques. They aren’t really a “cattle fly,” Hawkins says. They are more of a “people fly.” The house fly is attracted to filth and decaying matter.
“So, house flies are found on all kinds of livestock operations,” Hawkins said. “Since they are a filth fly, they tend to congregate anywhere they can find something to eat from the face of animals, around the feed bunk, spilled feed or the manure pile.”
Typically, the house fly feeds on manure, old feed, waste, sweat and tears. If they aren’t flying around the cattle, the house fly will rest on manure (decaying or fresh), soil, fences, weeds, trees, buildings and feed bunks.
“If they become overly abundant, they can be so much of a nuisance that the cattle will not want to be at the feed bunk to eat,” Hawkins says.
The biggest threat posed by the house fly is the large number of diseases it carries. Hawkins recalls that at one time the house fly was known to carry up to 65 diseases. They transmit disease just by landing on the cattle. Hawkins explains that they regurgitate saliva containing bacteria from wherever they were last, thus contaminating the new animal.
“They have a spongy mouthpart,” Hawkins says. “So, they sop something up when they are eating and then they go to the next thing. When they do that, they carry bacteria and viruses from the first spot to the second spot.”
Stable fly
Ranchers will be able to spot a stable fly problem within their herd almost at a glance. Since stable flies feed on the blood of cattle, they drive them into a bunch with their bites. When a rancher comes across their cattle bunching, they will most likely find flies around the lower parts of the cattle’s legs.
“The cattle are constantly milling in this huddle because they want to be the middle animal,” Hawkins said. “So, the closer to the outside the cattle are, the more they get bitten. The animals in the middle don’t get bitten because the flies don’t get that far into the group.”
The stable fly, Hawkins shares, not only delivers a painful bite but usually takes 2 to 3 bites before it gets a satisfactory blood meal. Without being controlled, the stable fly can cause a significant economic impact to a ranch’s bottom line, either through reduced weight gain or milk production.
“If cattle are being bothered by the stable fly, they will do a couple of things to protect themselves. They will go to the shade and try to hide in a bunch, or they get in the water to wade down to where the flies can’t bite their legs,” Hawkins says.
If the cattle try to control the flies on their own, they aren’t grazing. And not grazing means not producing milk for calves or not gaining weight for added pounds.
Horn fly
Like the stable fly, the horn fly causes pain to cattle but the bite is not quite as painful because their mouthpart is smaller. While the horn fly does feed on the blood of cattle, it tends to bite the back and sides of the animal rather than the legs. Producers will see their cattle swishing their tails frequently to shoo the horn fly away.
The horn fly lives most of its life on the cattle. This is different from the stable fly that only bites the cattle upon contact and then goes to rest on barn walls, fences, weeds, and other surfaces.
“They are the ones that make the black patches of flies on the backs of pastured cattle,” Hawkins says. “The horn fly typically bites about 30 times a day. If there are 1,000 horn flies on an animal, that animal is getting 30,000 bites a day for each fly to get a couple of drops of blood.”
With a biting irritation like that, cattle are, once again, likely to try to control the pest on their own by finding shade and not grazing, which interferes with a rancher’s economic goals. In general, Hawkins says that the absence of fly control could result in about 10 to 15 pounds of lost weaning weight or stocker animal gain.
Another way producers can distinguish a horn fly from a stable fly is by paying attention to the manure the fly tends to frequent. Both the horn and stable fly breed in manure. However, the horn fly will be in the fresh and undisturbed pasture manure, while the stable fly will be in the decaying manure mixed with vegetation.
Face fly
A distant cousin to the house fly is the face fly. The face fly is considered a “pasture fly,” though, like the horn fly. Both the face and horn fly breed in fresh, undisturbed manure and don’t spend much time in confined livestock operations.
“They are a ‘pasture fly,’” Hawkins says. “They look a lot like a house fly but are a little bit bigger. The face fly has a spongy mouthpart that is like the face fly and it tries to feed on mucus or tears.”
It is no surprise that the face fly is most likely to be found on the face of cattle. Nasal secretions and tears of cattle are ideal targets for the face fly to take in some protein. With their adaptation to be around the face of cattle and sponge-like mouthpart, they present the risk of transmitting bacteria and viruses.
“The real problem is that they go to the eyes of the animals and irritate the eyes with their mouthpart,” Hawkins said. “The key thing about face flies is the transmission of pinkeye. They can also transmit the Thelazia eye worm.”
The Thelazia eye worm isn’t the main risk; Hawkins says it is pinkeye in cattle. Pinkeye tends to leave spots in the cattle’s eyes even after it has been treated. This can cause cattle to be docked as much as $20 per hundredweight at a sale.
“Then, if you have an outbreak, treatment can be a real problem for producers,” Hawkins says. “Of course, there is also nothing worse than having a sore eye and this will impact their grazing as well.”
Identifying the types of fly species on cattle can help producers implement a better pest control management plan. Most of the products available for fly control work against only a few species. There isn’t a blanket approach because they are based on getting the pesticide to the flies relative to the flies’ location on the animal.
With this fly geography lesson, producers can make the most of their time and money to control one of the biggest nuisances — for them and their cattle.
Fly Geography is excerpted from the May 2018 issue of The Cattleman magazine.