Spring Cleaning Helps to Control Stable Flies

A good sprucing up around the ranch can go a long way toward controlling pesky, painful stable flies this spring.

By Ellen Humphries

In the spring months, thoughts turn to cleaning up around the place. Mild days and spring sunshine can help make it a pleasure to neaten up around the barns and pens.

If you add to your list of chores a good spring cleaning around the round bale feeder, then you will go a long way toward avoiding the hassle of pesky stable flies later in the season.

According to Dr. Bill Clymer, Amarillo, there has been a population explosion among stable flies, an insect with a painful bite and a thirst for blood (and money) from your herd.

“The single thing that has caused a major increase in the stable fly populations is the fact we went from feeding the little square bales of hay to the big round bales 20 years ago or so,” he says. “I used to never see pastured cattle with a stable fly problem. Now, just about anywhere in any of the ranching country I go to, in the summertime I’ll see a set of cattle out in the middle of a big pasture and they are all in a real tight ball.

“They are trying to get to the middle of the pack because the stable flies will bite the ones on the outside of the ring. The cattle are fleeing and after a point in time, they are trying to protect each other by swishing their tails,” Clymer explains. “Some will get heat stressed because they are so bunched up.”

Round bales themselves are not the problem. It’s the untidy detritus left behind which provides a paradise for the pests.

“When we feed the round bale in a big pasture of cattle, we’ll unroll the bale as we feed. They’ll clean up that bale almost completely and it’s not all in one spot. But,” he says, “I have three pastures with just a few head of cattle in them, so I’ll use a round bale feeder.” Those cattle then have access to that bale for up to several days.

Clymer continues to describe the scenario. “There’s always a lot of waste with the round bale feeders. It falls on the ground, the cattle trample it and lay on it and use it for bedding. They urinate and defecate on it. When it’s muddy, it gets trampled into the ground.

“What most of us have done in the past is this. In the spring, we kind of forget about where the round bale feeder ring is. We don’t worry about it until the next year when we take your tractor and get it out of where it’s settled in the mud,” he chuckles.

But Clymer thinks it is time to change our ways. “According to research done at Texas A&M, there can be more than a million stable flies breeding in one site where you’ve fed a round bale like I’ve just described.”

Stable fly habits

The University of Nebraska has a good description of the stable fly and its stages in life. “The stable fly is about the size of a house fly but is dark gray and has dark irregular spots on its abdomen. The proboscis (mouthpart) protrudes bayonet-like in front of the head. The larvae are typical whitish fly maggots. The pupae are chestnut brown and about one-quarter inch long.”

Clymer says houseflies have sponging mouthparts, while the stable fly uses its mouthparts to slice the skin, and “then they feed off the blood that seeps out of those cuts.

Researchers at Nebraska have found,  “The bite of the fly is painful and cattle attempt to dislodge flies by foot stamping, tail switching and by throwing their heads down toward their front legs. When flies are abundant, cattle bunch (each animal trying to get to the center of the group) or seek water to stand in to avoid the fly harassment.”

Nebraska research indicates stable fly infestations can depress weight gains by about a half pound per day. They also have a deleterious effect on milk production in dairy cattle. The bulletin goes on to say, “… stable fly population levels of five flies per front leg (counted on the outside of one leg and inside of the other) is the economic injury threshold. This is the point at which weight gains are depressed. It is indicated by the change in cattle behavior (described above).”

Clymer compares the daily routine of the stable fly to another common pest, the horn fly. “The stable fly is an opportunity breeder. One of the things that makes them hard to control is they fly in and take a blood meal, then they go land somewhere and basically roost to digest the blood meal. They don’t hang around the animal as much as the horn fly does. The only time the horn fly leaves the animal is to fly down to the manure pat and deposit eggs.

“When the horn fly leaves a manure pat, it actually starts flying in search of another animal, cow, horse, man whatever. Then, if it’s their normal host (cow or horse), they’ll stay on that animal taking a blood meal. The horn fly will feed 20 to 30 times a day, taking a small amount of blood each time. But the stable fly is going to go in and take a pretty large blood meal and then go land.”

Stable flies prefer to find a quiet, vertical place to roost to digest their blood meal. “This is the reason we see them a lot of times, in real heavy numbers, on the side of a feed bunk, or on the side of a barn. They’ll also go to a tree row and roost. They like a vertical surface.” Clymer says if there’s not a handy building, bunk or tree for roosting, the stable fly will roost on blades of grass or weed leaves to digest their meal.

“Then,” he continues, “they will seek out another host.

Stable flies earned their name because they actually prefer horse manure over cow manure. “Stable flies don’t really like straight cow manure that much,” Clymer says. “They used to be more commonly found in the area around the barns and pens.” However, if the cow manure is mixed with other organic matter, then the stable flies are attracted.

Stable fly season, he explains, has two peaks, depending on your location. “We have two weeks in the spring and maybe two weeks in the fall, it seems late May to early June and then the first part of September -- when we get our rains. When it gets hot and dry, their numbers are going to go way down.” However, “They have the ability to come back pretty quick.”

Although they are small, stable flies are hardy creatures. “There’s been some work done in Florida where they released marked flies, Clymer says. “They collected those flies 135 miles from the release site.” These strong fliers can also be carried in the high winds brought on by an advancing weather front.

“Some beaches on the East Coast had to be closed because they had stable flies,” Clymer remembers. Seaweed had washed up on the beach with the high tide. It started deteriorating a good way from the water’s edge and the flies made their home in it. “They were raising so many stable flies in that rim of sea weed along the coast that everybody abandoned the beaches because they were biting them so much.”

Chemical control

We can’t just ignore stable flies and wait for hot dry weather to take care of them. They are too painful and maddening to livestock. Clymer explains what tools can be used to reduce the problem.

Chemical control is one option. Clymer’s first statement about chemical control is, “Read the label and use the products that are registered.” After that, his advice about chemical control is to develop a regularly scheduled plan of treating the facilities and possibly the animals. It’s important to note there is no one-time treatment for stable flies. Repetition is the key. 

“Application to the animal is not very effective,” Clymer explains. “The flies come in, take a blood meal and leave. You may kill those flies that happen to be there right after you spray, but there’s not enough product in the endectocides, like Ivomec or Cydectin or Dectomax, to really get enough. It might affect reproduction a little bit, but we don’t see any real decrease in production from those products.”

In his more than 20 years in consulting with feedyards on pest control, he says he’s not a real strong supporter of spraying for pests everyday. “What I will have a feedyard to do is determine where those favored resting sites are and spray there with a residual spray. Some of the pyrethroids are safe and last for several days.”

However, being outdoors, a layer of dust is very likely to cover the treated area within a day or two, “so the fly is walking around on the dust and not the chemical.”

Even so, Clymer advocates a targeted spray plan rather than using a fogger or spraying the entire area. “We try to figure out where those roosting areas are in the hot part of the afternoon. You have to become familiar with your facilities.”

Interestingly, if a rancher wants to spray his or her cattle, Clymer suggests another spot treatment. “A problem with controlling stable flies with chemicals on the cattle is the stable flies like to feed from the knee and hock down, predominantly. They might not be on that animal except below the knees. If you do spray your cattle, the wet grass might wash it off, or the grass will wear it off, assuming the rancher has grass,” he says with a chuckle.

A dairy client of Clymer’s addressed this problem by setting up an electronic eye in a narrow alleyway at the milking facility. When the animal’s legs passed the electronic eye, a burst of insecticide was sprayed. “We did that as the cattle were leaving the barn. The insecticide would be gone the next day,” but the owner felt the 10 percent loss in production due to the stable flies was worth the effort.

Clymer does recommend various treatments for horses. “With horses there are the swipes, wipes, spray-on and sponge-on products that can be used. The downside is none of them are very effective for very long. As a horse perspires, it will wash off. It may give some avoidance if the flies come in and sense if that chemical is there and they won’t land on them.”

When asked if there are beef quality issues when using chemical treatments for stable flies. “Very definitely,” he answers. “Don’t apply products directly to the animal unless the label says to.

“Use care in applying it around the feed of the animal. Don’t spray in the feed bunk. Spray on the side and make sure it doesn’t spray over on the feed bunk. Many of these products would have residues. Check the withdrawal time if it is registered for cattle.”

Biological control

In recent years there has been a growing interest in using beneficial insects to control all sorts of pests. Stable flies have their insect enemies. “I recommend using parasitic wasps,” Clymer says. “Beneficial insects are one of the tools in the tool box that we can use in a pest management program,” but other measures must be in place.

University of Nebraska explains how the parasitic wasps do their job. “For the past several years, commercial insectaries have been selling pteromalid wasps for control of flies. These small wasps deposit an egg(s) within the pupal case of flies. The wasp larva feeds on the developing fly inside of the pupal case which usually results in the death of the fly.”

Clymer reminds us that it takes about three to four years to establish enough of a population of beneficial insects to control the flies. But, they are another tool to consider.

A different biological control method involves a bit of mechanics, particularly around horses. Clymer recommends either piling manure mucked out of stalls, or scattering it about to dry. If you choose to pile and compost the manure, consider pulling a piece of black plastic across the top of the pile to help raise the internal temperature and kill the larvae.

“A whole bunch of little piles around everywhere are not good,” Clymer says.

Best ongoing method: Sanitation

“There are three ways to control flies in any operation. Those three ways are sanitation, sanitation, sanitation,” Clymer says very plainly.

“If you can get rid of the breeding sites, you can pretty well get rid of the stable flies. You’re still going to have some coming in from your neighbors, but they are going to primarily come in on a strong wind. If you have just straight cow manure out in the pasture, the stable flies aren’t going to be breeding there. If the manure is mixed with straw or hay or grass clippings in an improperly designed compost pile,” that can be a source of problem flies.

Researchers at the University of Nebraska support Clymer’s statement, “Sanitation is the first step in a stable fly control program. In a feedlot or dairy operation, manure should be removed or mounded and packed. Clean around feed bunks and feed aprons, under fences and gates, around water systems and at the edges of the mounds. Clean sick pens and feed storage areas regularly. Even small breeding areas support very high numbers of flies. If sanitation is not practiced, chemical control may be unsuccessful.”

The impetus for this article was the statement that round bales being left out in the pasture during muddy winter months and into spring are prime breeding sites. Clymer explains, “The flies are not feeding in the bale, but in the round bale site. One of the first things we do after we’re through feeding hay is take the tractor or front end loader, or borrow a skid loader, and clean the pen out. That will substantially cut down the stable fly population.”

Clymer relates this example about a clean feedyard in Colorado that was, nonetheless, plagued by stable flies. “It literally was the cleanest yard I’d ever been in. I found no potential breeding sites. Usually those sites would be under the fence row or fresh cattle coming in where they’ve got hay in the bunk and it gets trampled in the ground. I found a few larvae, but there just wasn’t anywhere what would demand the number of flies that they had.

“The cattle on the southwest side of the yard were pushed away from the feed bunk. This was costing the feedyard money because the cattle were not eating when the flies were active. They were all pushed up in the northeast corner of the pen, so I knew they were coming from the southwest. The cattle on the other corners were not pushed away from the feedbunk.”

Since that part of Colorado looks a lot like the land around Amarillo, Clymer felt sure he could find the fly source by driving around. “About three miles from the feedyard there was a pole barn. There was no hay stacked in it, but I found they’d had alfalfa hay stored there. Alfalfa crumbles and leaves a trash everywhere. There were probably five or six inches of loose stems and leaves of alfalfa. About two weeks earlier, they had had a big blowing rain and it had gotten really wet underneath that roof.

“I took the toe of my boot and pulled some of it back and it was teeming with fly larvae. I went back to the feedyard and got some help and a front end loader and went to clean the barn out.” Clymer and his help spread the wet hay trash out in the sun where it would dry and where the birds could take care of the problem.

“Two days later the feedyard manager called me back and said, “You’re a genius. Who’d of every thought of that?’”

Another story shows the importance of properly storing feed. “Another place had feed stored on an asphalt storage area. They’d had a big rain and it soaked up underneath the stored feed. This was in an area that doesn’t rain very often and normally there’d be very little waste. I found that’s were the stable flies were breeding. I took a blade on the tractor and went around the ring to disturb it. That was enough to pretty well eliminate the problem.”

Clymer says there are some areas on a ranch where stable fly control is nearly impossible. “You’ll have places like leaves washing up in a creek. You can’t stop all of those, but if we can stop ones that we do, as owners and managers, that will go a long way to helping with the problem.”

Many of our readers will be aware of the development of new homes on a few acres, probably near your fences. Clymer has had experiences with these new subdivisions being a source of stable flies, instead of the ranch being the source.

“Stable flies are not only a livestock problem. They are a people problem and a pet problem. Stable flies actually create part of the ill feelings between us and our city cousins.

“People sit on their patio to enjoy a meal. If you have one or two hungry stable flies around, you can’t stay out there. I’ve been an expert witness in numerous lawsuits.” In one case, a development of homes on two-acre tracts had sprung up near a feedyard in northwest Oklahoma. “The ironic thing is everyone had a horse, cow or donkey. I was able to show there was stable fly breeding taking place in this housing development.

“The more urban our population becomes,  the more of these problems we’re going to have,” he predicts.

The tools available to the rancher for stable fly control are chemical, beneficial insect, and a good ongoing sanitation program at the ranch. Will people go back to using the small square bales? Probably not when there are handy round bale spikes that can be hitched on the back end of a truck.

“I’ve got a bale spike on the back of my ranch truck,” Clymer says. “I back up to the bale and spear it and drive to where I’m going, set it down, take my knife and cut the strings off it and I’m done.”

Done, that is, until it’s time to check the area to make sure it’s cleaned up, or go in and do some spring cleaning.

Editors Note:

Dr. Bill Clymer is a livestock parasitologist with Fort Dodge Animal Health. He started out his professional life as an ag teacher. After graduate school, he worked as an Extension entomologist for Texas A&M University for seven years, working primarily in the livestock area.

He ran his own business, Clymer Research and Consulting, for 23 years during which time he developed pest control programs for feedyards which contained more than a million head of cattle. His client list includes domestic and international businesses, as well as chemical, animal and pharmaceutical companies for which he did research.