Get to Know the Enemy: House Flies, Stable Flies, and More

Although there are over 650 species of flies in North America, there are only a few that are routinely found in equine environments. Do you know which ones are a problem around your horse?

Gathering intel on your enemy can give you the advantage when it comes to protecting your horse, especially as you learn fly traits and vulnerabilities. This is important because fly control products don’t work the same on all flies. Once you know the species you’re dealing with, you can check product labels to make sure what you’re using will be effective. “You have to properly identify the species you’re dealing with because the approach and products to control different species are different,” says Casey White, an entomologist and senior director of technical services and innovation at Farnam's Research and Development facility in Dallas. 

Stable flies or house flies?

Two of the most common species found around horses — house flies and stable flies — are considered “filth flies” because they breed in manure and/or decaying organic matter. Although they are similar in size, their mouthparts and abdomens are quite different in appearance.

Seven black circular spots are found on the gray abdomen of an adult stable fly. House flies don’t have a patterned abdomen.
For help identifying species, an internet search quickly turns up pictures of fly species. You can also take advantage of the Cooperative Extension Service connected with land-grant
universities across the country. To find your closest resource, just do an internet search for “local agriculture extension office.”

Which flies bite?

A major difference between common fly species? Stable flies bite. House flies don’t. 

Because they are blood feeders, stable flies have long, stabbing mouthparts to pierce the skin, so they can feed on blood. Both males and females bite.

House flies are an annoyance and can carry disease, but they don’t bite. They have sponging, sucking mouthparts designed for feeding on liquids. Houseflies continuously defecate and
regurgitate, which adds to unsanitary conditions.

Stable flies

Stable flies are a major pest to livestock all around the world. When feeding on large animals, such as cattle and horses, stable flies congregate on their legs, causing foot stomping and tail swishing.

“After they find an animal source for a blood meal and they’ve eaten, stable flies will leave the animal and go rest in a high shady spot,” says White.

Feeding time

In warm weather, stable flies prefer to feed in early morning and late afternoon. When the weather is cooler, they’ll feed at midday. If undisturbed, stable flies can get a full blood meal in five minutes. The underside of vegetation, fences. and shady areas of barns are prime resting spots for stable flies.

Stable flies reproduce in manure, soiled bedding, damp hay and feedstuffs. In fact, outdoor hay feeding areas are among their favorite locations, thanks to all the moisture and layers of decaying
hay mixed with urine and manure. This is a good reason to vary feeding locations and to regularly clean up and remove hay waste.

House flies

Don’t let the name fool you. House flies are commonly found around horses and barn environments. Since house flies breed in decaying organic matter, manure is a prime reproduction site, as is garbage and debris. They are also attracted to moisture and feed that has spilled.

“They might land on the horse’s body, but they are not feeding on blood,” notes White. “House flies either have to liquefy a solid before they feed. Or they feed on facial secretions around the nose and mouth of the horse.”

A fly mask offers crucial protection from house flies trying to feed on your horse’s face. Even though they don’t bite horses, these flies can irritate them, as well as spread bacteria and disease. House flies like to feed low, at a height of 4 feet or below, but they tend to rest high.

“If house flies are the primary pests in your barn, you can use premises sprays and scatter baits to target those fly populations,” says White.

“House flies will rest up high, like on barn rafters,” he adds. “This is why sticky tape and sticky traps work well on them. If you put tapes and traps high where flies go to rest, they will encounter them and get trapped.” Fly sprays like Farnam’s Bronco®e Equine Fly Spray can provide effective barn protection when used with a regular tank sprayer.

Protect against stable flies and house flies

Many of the same chemical and non-chemical methods protect horses while controlling both stable and house flies.

These methods include:

• Manure and vegetation management

• Remove waste hay, soiled bedding, damp vegetation

• Use premises sprays/traps/sticky tape

• Apply on-horse fly repellent sprays

• Stable horses during peak fly activity

• Install screens in stalls/barns

• Use physical barriers like fly masks, boots, sheets

• Use a feed-through fly control product

You can take a proactive approach by using a feed-through fly control product that targets both house flies and stable flies. “Start this before you see fly activity and continue through fly season to minimize the number of flies breeding on site,” advises White, who recommends horse owners consider a feed-through fly control product like Farnam’s SimpliFly® with LarvaStop™ Feed-Thru Fly Control. Starting early in the season can prevent the fly population from becoming a problem. For best results, all horses on the premises should be on a feed-through.

Beware of other blood-feeding flies

Horn flies are blood-feeding flies that commonly feed on cattle. These small black flies are often seen clustered on the shoulders and backs of cattle and will move underneath the animals during the heat of the day. Once these blood-feeding flies complete their development, they seek a host animal.

They will feed on horses if cattle aren’t available. “Horn flies can be a problem with horses only if cattle are in the vicinity and close enough that those horn flies have emerged from cow manure. Even if they migrate in from neighboring cattle, horn flies can’t maintain a population only with horse manure,” explains White, noting that horn flies specifically reproduce in cattle manure, not horse manure. You can protect your horse by using on-horse repellent sprays that are effective against horn flies.

What about "horse" flies?

Some people refer to any flies found around horses as “horse flies,” but the horse fly is a distinct family. “People call flies by different names in different areas and use the common names incorrectly. This is why the scientific community uses the Latin names for species identification,” says White. Horse flies and deer flies are both blood-sucking flies of the insect family Tabanidae.

Deer flies are blood-sucking flies that are readily identified by their yellowish-orange and black bodies. Often found in wooded areas, deer flies are smaller than horse flies, but the females inflict a painful bite. Deer flies will bite humans as well as horses.

Unlike stable flies and house flies, horse flies and deer flies don’t reproduce in manure. Instead, their larvae develop in the mud and wet soil along the edges of ponds, stream banks, irrigation or drainage ditches and wetland areas. Both species are opportunistic feeders, and horses can easily be targeted. “Horse and deer flies will use tree lines as protection and wait for animals to come to shade in the summer,” says White.

Since horse flies and deer flies don’t hang around the barn or stable area, sticky tapes, scatter bait and traps are not effective against them. Use on-horse repellent sprays instead. If you have problems with any biting flies — stable flies, horse flies, deer flies or horn flies — you’ll want to use on-horse repellent products, like Tri-Tec 14® Fly Repellent.

What attracts flies?

We already know that manure and organic matter, including damp hay and vegetation, attract house flies and stable flies, but what about the horses themselves? You may have heard that some horses are more attractive to flies than others. “Color may play a role and some animals may emit an odor that’s more attractive to flies, but we can’t say for sure,” says White.

“Certainly, in the cattle world, we see that a lot of lighter colored breeds may have fewer flies than dark-colored,” he notes. “Thicker-skinned cattle breeds, like Brahmans, also make it harder for biting flies to get a blood meal,” adds White. Following this line of thinking, thin-skinned horses may be more vulnerable to biting flies simply because it’s easier for them to pierce thin skin and feed on blood.

Do flies chase horses?

You may have seen horses gallop off across the field to get away from flies. Will flies actually chase horses? In some cases, yes. Bites from blood-feeding flies are painful. And horses who have experienced this will readily flee to avoid being bitten again. “Horse flies and deer flies may chase horses because they are dependent on blood meals,” says White. Bot flies don’t bite horses, but the females lay their eggs on the ends of hair shafts in different spots on the horse. These bot flies are annoying as they loudly buzz around the horse trying to land and lay eggs, so horses often run from them.

“Bot flies sometimes chase a horse because they are dependent on laying eggs on them,” adds White. But the most common fly species — house flies and stable flies —don’t typically chase after horses.