If you see your cattle stomping their feet during warm summer months, it might mean they’re dealing with stable flies. Stable flies look a lot like house flies, but they are blood-suckers with bayonet-like mouthparts they use to pierce the skin. They prefer feeding on the bellies and legs of their victims, which include horses, cattle, hogs and humans. Though they only take a few drops of blood at a time, their bites are so painful that cattle stamp or kick to try to rid themselves of the pests. Just fifty flies per animal can reduce feed efficiency by 10 to 13 percent.
Prevention is the Best Defense
Your first line of defense is good sanitation. Stable flies breed in wet straw and manure, spilled feds, silage, grass clippings, and other decaying vegetation. They can also breed in the rotted hay at the base of large, stored hay bales.
Each female lives 20 to 30 days and produces about 500 eggs. It takes about 3 weeks for the egg to become and adult fly. By removing and thinly spreading potential breeding habitat once a week – like manure, bedding, moist hay and spilled silage – you kill eggs, maggots and pupae and reduce breeding habitat. Watch out for other fly sources like wet feed in the ends of managers and underneath feed bunks, green chop and spills around silos, and mud and manure along fence lines.
Fly Paper and Parasitoids
If your stable fly problem is in a building, you can use an old stand by. Sticky tapes, fly paper and sticky ribbons (especially the giant ones) all work well to catch and reduce fly populations.
Stable flies also have naturally occurring enemies. Beetles and mites eat fly eggs. Parasitoids, like Muscidifurax raptor, are small wasp-like insects that attack fly pupae. When the female finds a pupa she stings it and feeds on it, killing it. Next, she uses her stinger to lay an egg in the pupa. The egg turns into a young adult parasitoid feeding on the pupa and eating its way out of the shell to start the cycle all over again.
The problem for the parasitoids is that flies develop twice as fast from egg to adult, lives longer, and lay more eggs. So if we don’t intercede, we’ll always have fly problems. Parasitoids also lag behind flies in developing pesticide resistance so when we use them, we kill more and more beneficials, and fewer flies. If you want to work with parasitoids, and you’re also using pesticides be sure to check that your pesticide is compatible with them.
Adding Parasitoids to Your Farm/Ranch
Many companies sell parasitoids, but you need to be sure the kind you buy work in your region. You can check with your local extension entomologist to find out what will work best for you. They’ll arrive in as immature insects in killed fly pupae, often in cheesecloth bags. Hang these bags on posts and rafters in areas where stable fly breeding is a problem. If you’re using them with calves in calf hutches, place 3 heaping teaspoons of pupae (about 1,000) in the hutch each week. You’ll need about 200 per cow or 1,000 per calf hutch per week starting in middle to late May. (As always, results depend on local factors and the number and timing of your releases may need to be adjusted to meet your particular needs.)
Prices vary, but the average is about $13 plus shipping per batch of 10,000 parasitoids. At a rate of 200 per cow per week, your cost will be between $2.60 and $4.70, depending on how many weeks you release them. Researchers have compared the cost of parasitoids and insecticide treatments and found that use of parasitoids reduces insecticide treatments by 80% and results in 50% fewer flies.
Thanks to Lee Townsend, University of Kentucky Extension Entomologist, and to Wes Watson, Keith Waldron and Donald Rutz of the Department of Entomology at Cornell University for sharing information for this article. If you’d like to read more, check out “Integrated Management of Flies in and around Dairy and Livestock Barns.”