Fighting Flies Requires A Multi-Pronged Approach

May 31, 2007 - 10:00 PM
As summer's heat rolls in, so do the flies. Photo courtesy of

Controlling nasty, horse-tormenting bugs isn’t just about stinky sprays and oily wipes anymore. It’s a multi-front battle with an array of innovative weapons.

Once upon a time, all we wanted was to see the flies gone. Each summer, as they swarmed, buzzed, bit and tormented our horses, we were willing to do just about anything to get rid of the little pests.

Ever since flypaper was invented (in 1861, for you trivia buffs), humans have been tirelessly applying themselves to the Battle of the Bugs—and though we may never win the war, we’ve certainly triumphed in some of the skirmishes. Science, inspiration, and experimentation have given us quite an arsenal with which to attack and repel flies. From electric bug zappers, to pheromone traps, to parasitic wasps that feed on fly pupae, we’ve explored all sorts of ways and means of getting rid of flying insects.

But today there’s more at stake than simply eradicating the enemy. Now we want to be able to do it in an environmentally responsible, low-impact way, without poisoning the landscape, our horses, or ourselves. We’re learning that there are sometimes long-term consequences for the actions, which, in the short term, increase our comfort level in riding rings and barns.

The good news is many methods of fly control are more environmentally friendly than you’d think at first glance. And we could be employing many more. Here’s a run-down of some fly control methods you’ve probably used, and a few which may be new to you.

Spraying And Spritzing

The cornerstone of any fly counter-aggression program is a bottle of fly spray. Though nothing’s perfectly able to keep the bugs off our equines, fly repellent formulas do work to some degree. But with their chemical smells and lists of barely-pronounceable ingredients, it’s not unreasonable to wonder just how toxic these products really are.

Take heart. Almost all of the fly repellents formulated for horses are based on a chemical called pyrethrin, which is extracted from dried chrysanthemum flowers, grown as a crop in Kenya, India and a few other equatorial regions. The broad-spectrum bug-repellent properties of these plants have been recognized as far back as 400 B.C. When pyrethrin is applied directly to insects, it has a powerful “knockdown” (instant kill) effect, plus it has repellent properties—and what’s more, it quickly decomposes in sunlight, leaving no harmful residues. As chemicals go, pyrethrin is about as environmentally friendly as you could ask for.

Most flying insects are highly sensitive to pyrethrins, which means you don’t have to apply heavy concentrations of chrysanthemum juice for it to work. At the same time, it’s quite non-toxic to most mammals, though fish and other forms of aquatic life are very sensitive to its effects, so you should be careful never to dump pyrethrin in a water source. Birds are also somewhat sensitive to the compound.

The problem with pyrethrin is its very biodegradability, which limits its efficacy, on its own, to an hour or two. So manufacturers have come up with all sorts of clever ways to lengthen its lifespan, such as adding a sunscreen to their fly spray formulations. Horse people may assume the sunscreen is there to protect their horse’s skin, but in fact it’s there to protect the pyrethrin! Synergists such as piperonyl butoxide, or PBO (derived from the sassafras tree), which help to create a longer-lasting protectant effect, are also common.

Chemists have improved on nature by formulating a vast array of synthetic versions of pyrethrin. These “pyrethroids” avoid the problem of fluctuating availability and are also designed to have a more lasting effect than natural pyrethrin—though they, too, are biodegradable. There are literally hundreds of synthetic pyrethroids, of varying strengths, and they have improved significantly on pyrethrin’s length of action, sometimes remaining effective for up to a couple of weeks.

The big problem with the synthetics is that many species of flies are resistant to them. Jerry Butler, Ph.D., a medical and veterinary entomologist with the University of Florida, has done extensive studies on fly repellents and insecticides. He notes, “Permethrin [a synthetic pyrethroid] used to last three days. Now it’s only effective for a couple of hours.”

So it’s not your imagination—your fly spray probably is less effective than it used to be. But interestingly, no resistance has yet been noted for natural pyrethrin.

In response to these resistance problems, manufacturers have been forced to combine ingredients in order to provide that initial fly-killing effect and a residual, long-lasting repellent action. It’s common to see fly sprays that contain both natural pyrethrin and a synthetic pyrethroid, plus PBO.

Citronella oil, extracted from a relative of the culinary herb lemongrass, is another common fly spray additive, which adds a citrus odor. Its main action is to repel mosquitoes (against which it can be quite effective). A related lemongrass extract called geraniol, which was originally investigated at the University of Florida, is also starting to find its way into products for horses.

How Safe Are They?

When you saturate your horse’s skin with a fly spray, hoping to get enough repellent action to enjoy a one-hour trail ride, are you putting his health at risk? What about when the wind changes as you’re spraying and you get a lungful of the product yourself?

The ever-watchful Environmental Protection Agency reviews the safety quotient of pyrethroids about every five years and continues to approve them, which is both an indication of their safety margin and of the fact that there are very few alternatives.

PBO has been suspected of causing chronic liver and kidney damage in test animals at very high doses (over 1,800 mg/kg of dermal exposure in rabbits). As an enzyme inhibitor, it’s also suspected of causing convulsions, hyperexcitability, skin irritation, and prenatal damage in humans exposed to extremely high doses. But at the concentrations found in fly repellent sprays, it has a good margin of safety, and unlike pyrethroids, it’s not particularly toxic to fish.

Still, it’s important to read a fly repellent’s warning label before you start spritzing it all over your horse. Some may recommend you wear gloves; all will recommend you avoid spraying it near your horse’s eyes, mouth, and nose (you can safely apply repellent to the face and ears by spraying it on a soft towel and then wiping it on your horse). And, of course, you should limit your own exposure to the spray as much as is practical.

Keep in mind as well the toxicity pyrethrins have to various kinds of aquatic life. Avoid contaminating any water source with it, and don’t spray it near your hay bales or grain bags, either. That’s why stable-wide misting systems, popular a decade or two ago, might not be a great idea: it’s difficult to avoid getting feed, water buckets and bedding saturated, resulting in your horse ingesting larger quantities than you’d intended.

Stealth Attack

Chemical warfare isn’t the only way to keep flies in check. There are lots of other ways to reduce the squadrons in your local area, ranging from sticky tapes, pheromonewafting traps, and granular fly baits, to electronic bug zappers (which have fallen out of favor now that we know they kill mostly moths and non-biting flies) and propane-powered units that fake being a tasty mammal (chemically speaking).

Virginia horseowner Kirsten Wingenbach undertook a comprehensive survey of fly control methods a couple of years ago when her boarding stable, near a marshy area, wanted to institute a barn-wide program. The process, she said, was quite an education. She became a fan of nature’s own double agents, fly predators, which infiltrate and destroy populations from within.

These tiny parasitic wasps lay their eggs in the pupae (cocoons) of pest flies such as houseflies, horn flies, and face and stable flies. Their own larvae then devour the pupae of their hosts and prevent them from ever maturing to the flying stage. Unobtrusive and utterly harmless to humans and horses (they don’t bite and have no stingers), fly predator wasps are commercially available by the thousands and can go to work whenever they’re spread on or near fresh manure where pest flies will be laying eggs.

The only downsides are that they need to be re-applied monthly throughout the fly season, and that because they don’t travel far, you won’t see much of a reduction in flies if your livestock-keeping neighbors don’t follow suit with a similar program. They’re also somewhat sensitive to cold climates, so probably won’t work in Alaska or most parts of Canada, though some suppliers provide a mix of species with varying degrees of hardiness.

“Also,” said Wingenbach, “any insecticide you are using on your horses will kill your fly predators too, so it’s best to designate an area away from where you’ve applied them, where you put fly spray on your animals.”

The other main way to attack flies before they mature is by using “feed-through fly control” products, which make your horse’s manure a hostile environment for fly breeding. Added like any other feed supplement, they’re designed to pass through your horse’s system untouched but are toxic to flies, which gather around the manure pile later. There are two basic types of feed-through products: organophosphates (usually a chemical called Rabon®), which act as a nerve agent to kill larval flies, and insect growth regulators, which interrupt the growth of chitin (which makes up the insect exoskeleton) and prevent the bugs from maturing, while remaining harmless to beneficial insects and mammals.

The advantage of feed-through products is that they can help keep fly populations down generation after generation. But like the fly predators, they’ll be of only limited use on your property if large populations of flies are congregating at your neighbor’s. You’ll also want to read the label carefully to see which type of feed-through product you’ve got.

Insect growth regulators have a wide margin of safety and no reports of adverse effects (so far), but one organophosphate product (Farnam’s Equitrol) was involved in a California lawsuit in 2004, in which a jury awarded more than $1 million in damages to plaintiffs who claimed the product caused or exacerbated a variety of health problems in their horses. The prosecution successfully argued that although the product has a wide margin of safety in cattle and other livestock, that the product is not inert when fed to horses and that some degree of organophosphate is absorbed. Farnam changed the formula so that it is no longer an organophosphate, and the new product is called Equitrol II. Farnam also offers a new feed-through product called SimpliFly, with LarvaStop®.

Wingenbach noted that the Rabon-based feed-through products remain popular because they are considerably less expensive than the insect-growth-regulator types.

Traps And Tricks

Trapping and killing flying bugs should be as simple as hanging a couple of dollar-store sticky traps in your barn, but it isn’t. You need a multi-pronged approach that uses everything we know about the behavior of the enemy, because different types of flies are attracted (and duped) by different things.

House and stable flies, which swarm in barns, around horse’s faces, and near the manure pile can often be bumped off by granular bait or simple sticky traps placed in high-traffic areas. They’re attracted to the color yellow, and trap manufacturers may use a combination of the color, attractant pheromones, and/or sweet smells to lure the bugs to their doom. Various types of bottle traps (flies get in, but can’t get out) use similar strategies and have the advantage of not getting stuck in your hair.

But mosquitoes are trickier creatures; they’re attracted to the carbon dioxide plume” any breathing animal emits. Electrical or propane-powered units that fake that carbon dioxide plume and then suck up the mosquitoes are one way to rid your immediate area of the little blood-suckers, but they’re expensive: one that will cover a one-acre area will set you back between $300 and $700. Or you can settle for the low-tech solution, which is to eliminate sources of standing water where mosquitoes breed. That includes bird baths, rainbarrels, gutters, and tire jumps (drill a few holes for drainage). Don’t forget to dump out your paddock water troughs every couple of days to abort the mosquito larvae lifecycle.

Possibly the most pesky of all the flies to eliminate are the Tabanidae flies, which include those vicious little deer flies, huge horseflies that zero in on the top of your horse’s rump (among other places), and the nasty yellow flies that are so problematic in Florida. No method for larval control of these fanged beasties has yet been developed, and most commercial fly sprays repel them modestly at best. But they can be trapped, using a strange contraption sometimes called a “Manitoba fly trap” (Directions for building a Manitoba fly trap.) Above all else, these flies are attracted to movement, so the essential ingredient in a Manitoba fly trap is a black ball suspended on a string, which apparently simulates an animal well enough to lure the flies in.

Blue is another color to which these bugs respond (deer flies, in particular), and some researchers have gotten good results out of painting a plastic nursery pot bright blue, covering it in “Tanglefoot” insect-sticking spray (available at garden centers and hardware stores), suspending it on a pole or arm (so that it rattles and shakes), and slowly trolling around the property, at a speed under 7 miles an hour, with the trap attached to a pickup truck or a riding lawnmower. If you can stand the humiliation, they even recommend parking an upside-down blue plastic drink cup, coated in sticky spray, on top of a baseball cap and going for a stroll through the pasture! Deer flies usually fly at heights lower than 10 feet and will attack the highest available area on the human (or equine) body first. (Note: Tanglefoot can be problematic to get off your hands, but hand cleaners with a citrus base will do the trick.)

What’s Best For You?

Deciding which type of fly control program will work best for you depends on a number of factors: the size of your operation, which types of bugs are most problematic in your area, whether you have neighbors with livestock, your degree of sensitivity to environmental issues, and of course your budget. Many products are designed to protect only a certain number of horses or a certain acreage, so factor those specs into your calculations. Too little protection is about as useful as none.

At Wingenbach’s barn, which housed about 30 horses, the boarders eventually decided on a combination of simple traps and a feed-through organophosphate. “Personally, I would rather have used the growth regulator product,” she said, “but it was about four times the price.”

Her analysis helped her to make an informed decision about fly control now that she keeps her horses at home on a small acreage too. She relies on regular applications of eco-friendly fly predators in and around her manure pile, and baited, compostable traps near her barn. She may consider installing a Manitoba fly trap if those methods don’t control all the bugs. Armed with information and the right tools, you too can win the battle, if not the war.

A Few More Fly Control Tips

•    Use simple sticky traps, but not those with attractant chemicals, in the barn—the attractant will lure more bugs into the building. Attractant traps are most effective on the perimeter of your property.
•    When temperatures exceed 80º F, flies feed and rest on the ground, so place your traps low as temperatures soar.
•    Only use fly baits in areas well out of reach of children, horses and pets, and dispose according to the manufacturer’s directions.
•    Keep feeds covered and don’t let spills accumulate on the floor (this includes pet foods for your barn cat or dog).
•    Remove manure from your property as often as possible, and be careful of pesticide run-off into water sources.
•    Use barrier methods, such as fly masks, sheets, and leg wraps, to increase the degree of protection from biting bugs when your horse is turned out.

If you enjoyed this article and would like to read more like it, consider subscribing to the Chronicle. Check out the table of contents to see what great stories are in the magazine this week.

Category: Farm Management

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