It’s just a fact of life that living outside means dealing with insect barrage in warm months of the year. Most times, the trouble with insect attacks on horses is more of a bother than anything. But insects also serve as vectors for significant equine disease. In this series of articles, let’s look at some of the insect characters that carry disease, and the risks those diseases pose.
Biting flies emerge in warmer months, but at different times depending on the species. Habitat differs, as well: Sand flies are most prevalent in dry areas; biting midges like wet and moist areas; black flies flourish in aquatic habitats with flowing water. Yet, once hatched in these areas, the flies are free to travel and disperse:
- sand flies don’t go far, maybe up to 100 yards;
- midges might fly 2-1/2 miles or be carried hundreds of miles by wind;
- black flies can travel 7+ miles per day over a lifespan of up to three weeks.
Stable Flies, Face Flies, House Flies, Horseflies and Deer Flies
House flies, face flies and stable flies love to feed on eye secretions, and by their very presence, stimulate more drainage from the eyes. These flies hatch in manure, wet bedding, garbage and debris. Timing of appearance differs—houseflies flourish in hot weather; face flies and stable flies are active from spring into early fall. Horseflies and deer flies like to feed in sunshine.
In some instances, houseflies, face flies and stable flies can transmit Habronema larvae in moist areas as found around the eyes, mouth, nostrils, penis, sheath, udder and in wounds. These larvae induce a reaction that delays healing in wounds. Face flies also transmit a worm, Thelazia lacrymalis, into the tear ducts of the eye and eyelid glands, leading to chronic irritation.
Ticks transmit a number of diseases to horses, including Lyme disease (Borreliaa burgdorferi), anaplasmosis and piroplasmosis. Ticks attach to deer and rodents, and thereby are carried to other areas. Horses living next to transition zones—pasture turning to brush or wooded areas—are more at risk for tick bites.
Each fly species has preferential feeding times—Sandflies mostly feed at night; midges mostly prefer the hours surrounding sunset and sunrise; black fly activity tends more to daytime and early evening. This makes for difficult management strategies to control pest attacks on horses. An ideal strategy is to move horses away from insect habitats—or at least remove them from pasture and away from water sources—during typical insect feeding times.
Another option is to stable the horses during high-risk periods. Fans can help to deter insects entry into the stabling areas or at least shorten landing time on the horse, so the insect doesn’t have time to feed. Screens with fine mesh, fly masks, fly sheets, leg mesh wraps, and mesh belly-bands are helpful.
Pesticides (pyrethrins) are useful against adult insects when used directly on horse skin. Wounds should be covered as they serve as attractants for insects. Propane-fueled insect traps that emit carbon dioxide might collect a sufficient number of insects within a breeding habitat, but they are relatively ineffective in windy areas. It is notable that fly zappers in and around barns can actually be an insect attractant at night.
Effective on-site drainage is important around gutters and water tanks to mitigate propagation of mosquitoes and biting insects. Fill in low spots on your property with sand or gravel. Keep vegetation cut short for control of biting midges and black flies, ticks and mosquitoes. Aphids also live in standing vegetation and are an attractant to black flies and mosquitoes that feed on aphid excretions of digested sap and sugars.
Any vessel or area that can hold water is a potential mosquito reservoir: Gutters, flowerpots, buckets and cans, swimming pool covers, wading pools, discarded tires, wheelbarrows, bird baths, pet bowls and tractor buckets, to name a few. Even a hoof print in mud or near a water tank can hold a water depth conducive to hatching of mosquito larvae. Turn containers not meant to hold water upside down or drill holes in the bottom for drainage.
Clean stock tanks weekly to eliminate organic debris that would otherwise be an attraction to breeding mosquitos. Manage sluggish creeks and ponds with aeration systems and larvae-eating fish to mitigate them as mosquito habitat.
Apply “dunks” and “bits” containing soil bacteria called Bacillus thuringiensis sub. israelensis (BTI) or Bacillus sphaericus (BS) to water surfaces as a granule or floating briquette to control mosquito larvae, blackflies and some midges.
Ticks favor temperatures above 40 degrees Fahrenheit to be active. They prefer woodlands and areas of tall grass, piles of leaves and other vegetation, and especially can be found at the boundaries of these ecosystems. They tend to avoid sunny, dry areas, particularly if lacking in protective vegetation. Control can be accomplished by fencing horses away from the woods and other areas of dense brush and vegetation. Mouse traps and rodenticides around the barn and paddocks help to diminish mouse populations that carry ticks. Mow pastures to remove tall grass, particularly in areas not often grazed. Apply pesticides at the edge of wooded areas. Clear away shrubs and vegetation along wooded boundaries and fence lines to reduce favorable tick habitat.
Chickens, peahens or guinea hens are also a useful and environmentally friendly means for control of tick populations.