Combating Flies with Biology
/By Michael Hipp
May 2020
As we’ve all been sequestered due to the pandemic it has been nice to finally see the sun and know that summer is just around the corner. However, as a horse owner, you know that this time of year is the time when we, our horses, and barns begin to deal with another plague – flies.
In relation to horses I do not use the term “plague” lightly when it comes to flies, for there are over a dozen different types of flies that pester and attack our equine companions – blue blowflies, black blowflies, deer flies, horse flies, flesh flies, green bottle flies, horn flies, face flies, biting stable flies, bot flies, cluster flies, and the common house flies. Flies will cause your horse to stomp, bite itself, swish its tail at the wrong time (usually filling your face with it), shake its head, and sometimes run through the paddock in an attempt to get away. Flies can also carry diseases, such as face flies which can transmit pink eye, or bot flies that can cause extreme damage. Along with everything else there is to manage on a horse property, flies can be one of the most frustrating challenges to deal with. Fortunately there are plenty of methods to choose from, and one of my favorites is to use biology.
pHOTO CREDIT: USDA
Biological methods of fly control have become very popular in the last decade. One of the most popular tools today is to use what are called “Fly Predators”or “Fly Parasites”. What these are is actually a small, parasitic wasp of the Pteromalidae family that is the naturally occurring enemy of flies. They are nocturnal and completely harmless to humans and horses, but deadly to flies. The female wasp seeks out the fly eggs, drills through its cocoon, and lays several eggs in it. The wasp young then kill the fly in its egg stage by eating it. These wasps reproduce in one to two weeks and are adapted to all climates.
It is recommended that for best results, start using the wasps before flies become a problem. Flies can travel up to a quarter mile, but these wasps rarely go further than 300 feet, so placement is very important. You will want to place them near manure and in any organic matter around the barn where you observe flies. The number of wasps you use is dependent on many factors, such as the number of horses you have and the size of your paddocks and pastures. The company you purchase them from will provide guidance for that.
One thing to keep in mind about these wasps is that while they are excellent at destroying flies in their egg stage they do not attack adult flies. So, the biological combating of flies must also include other tools to take care of the adult flies. Some of the best tools are birds and bats.
I have always tried to encourage barn swallows in my barn. Aside from being a beautiful bird, barn swallows consume about 60 flying insects and hour and up to 850 a day! A lot of folks have commented that barn swallows are difficult in a barn or stable because of the poop they always leave under their nests. I put a board underneath any swallow nests to catch the poop, and it can stay there because swallows will reuse nests from year to year.
You can encourage swallows to nest in your barn in a few ways. One is to leave doors open on your barn and allow the birds to fly inside. You can also leave a wheelbarrow or 5 gallon bucket with mud nearby to provide them materials to build their nests. Or you can build artificial nest cups out of wood and place them under the eaves of your barn, where they can be protected from sun and rain.
Even better than swallows, however, are bats. Bats are nocturnal, so while swallows hunt flies during the day the bats will be hunting them at night. And do they ever! In fact, a bat will consume 1,200 flying insects and hour and almost 10,000 in one night. The best way to encourage bats is to build a bat house, mounting it on your barn in a sunny location. The Conservation District can provide design and mounting ideas for you any time.
The battle with the flies is only just beginning this season, but if you enlist a little biology, victory can be assured.
This project has been funded wholly or in part by the United States Environmental Protection Agency under assistance agreement PC-01J18001 to the Washington State Departments of Health and Ecology. The contents of this document do not necessarily reflect the views and policies of the Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.
