Barn Fly Facts

Are you and your horse plagued by barn flies? Take our quiz to test your fly IQ.

June Brigman

When it comes to waging war, you can never know too much about the other side. So, if you want to win that War on Flies, grab a pencil and take our quiz. Chances are, you’ll learn some fun fly facts to share around the barn and boost your fly-warfare expertise. 

[READ: Vesicular Stomatitis—What You Didn’t Know from a Vet in the Heart of It]

Test Your Fly IQ

Question 1: Flies are involved with the spread of many different diseases, including:

a) Strangles.

b) West Nile virus.

c) Rabies.

Question 2: The amount of distance a typical urban house fly will cover in a day averages:

a) 1,000 yards.

b) 3 miles.

c) 20 miles.

Question 3: How long does a typical fly live?

a) 24 hours.

b) 4 to 5 days.

c) 30 days or more.

Question 4: What is the buzzing sound a fly makes?

a) Vibration of tiny hairs on the fly’s body as he moves through the air.

b) The beating of the fly’s tiny wings.

c) The fly’s legs repeatedly rubbing together.

Question 5: How many eggs does a female fly lay in a batch?

a) 75 to 100.

b) 1,000.

c) 10,000.

Question 6: Describe a fly’s field of vision.

a) A fly has blind spots directly in front of and behind its body.

b) A fly can see 360 degrees around its body.

c) Flies don’t see well at all—they primarily function by feeling vibrations.

Question 7: How do flies eat?

a) Flies have moveable mouth parts that allow them to bite and chew their food.

b) Flies collect nutrients on their feet then transfer them to their mouths.

c) Flies suck up liquids with a proboscis.

Question 8: What is the typical “flight plan” for a fly in motion?

a) A fly can only travel in a forward direction—that’s why they circle around.

b) Flies can hover, fly vertically, and fly forward and backward.

c) Flies can hover and jump backward, but only fly in a forward direction.

Question 9: How resistant are flies to different types of repellants?

a) Resistance varies between groups of flies according to location.

b) Flies are sensitive to most repellents, when properly applied.

c) Fly repellants are completely worthless.

Question 10: Do flies have any redeeming features?

a) None at all. Flies are nothing but a nuisance.

b) Even though it’s disgusting, they do serve a purpose when they eat decaying matter—but that’s about it.

c) Flies have quite a bit to offer. They eat other types of pests as well as decaying matter, and, just like bees, can play a part in pollination.


1. (a), 2. (a), 3. (c), 4. (b), 5. (a), 6. (b) 7. (c) 8. (b) 9. (a), 10. (c)

[READ: 7 Fly-Fighting Solutions]

How’d You Do?

Question 1: Answer A

Strangles is just one of many diseases that flies can transmit—ranging from fly-bite allergies, conjunctivitis, and local irritation to life-threatening viral diseases like equine infectious anemia. For the record, however, we can’t blame flies for everything. Other diseases, such as West Nile virus, are transmitted by mosquitoes. Rabies is most commonly passed directly in saliva from a bite.

Question 2: Answer A

Flies go where the food is, so an urban house fly doesn’t have to travel far to find a meal. Plentiful trash that’s close at hand means the typical urban house fly doesn’t travel much farther than 1,000 feet on any given day. But if you move that house fly to the country? He may travel 7 miles—or more—to find a good source of manure. What does that mean for you? Keep manure picked up around your farm, and your flies may decide to move away. Interestingly, if you compost manure properly it’ll actually repel flies because it generates too much heat to make them happy.

Question 3: Answer C

Flies live longer than you may think. The average lifespan is 30 days or more for most fly species. Some, like horseflies, can live for years. The total lifecycle of a fly has four stages: egg, larvae, pupa, and adult. Under ideal conditions, an egg can hatch in as few as eight hours to become a larvae—commonly known as a maggot. Maggots feed on manure, rotting food, and other filth, and must shed their outer layers or “molt” before they pupate (develop fly-like characteristics such as legs and wings). As a general rule, all stages of the fly’s life cycle thrive when temperatures are warm and food is available. They’ll pass through each stage more efficiently, and adults will live longer (meaning they can lay more eggs). That’s why tending to manure and garbage is essential for keeping flies at bay. It also explains why warm spring weather typically marks the beginning of your annual War on Flies.

Question 4: Answer B

A fly’s wings beat as fast as 1,000 times per minute. That’s what creates that buzzing sound you hear. In spite of that, it’s hard to believe that flies don’t move all that fast. In fact, the top flight speed for a typical fly is around 4 to 5 miles per hour (a brisk walking pace). So why are they so hard to kill? They’re incredibly acrobatic. When you’re trying to chase down a fly, outrunning him shouldn’t be a problem. Outsmarting him by predicting the direction he’ll move is the challenge. Picture this scenario: You’re riding your horse, when he starts being chased by a determined bot fly. If you’re like me, you’ve probably dismounted on a few occasions so you could chase the fly around in circles in an attempt to swat it. Frustrating, right? Next time, consider breaking into a gallop (or even a brisk trot) to escape the annoying pest.

Question 5: Answer A

A female fly typically may lay as few as 75 to 100 eggs per “batch,” but that’s only the beginning of the story. A female will begin laying eggs 10 to 12 days after she matures, and she can lay five or six batches in her lifetime. These eggs will hatch in less than a day. A group of scientists calculated how many flies would accumulate over time if a single pair were allowed to breed completely unchecked (i.e., all of their offspring survived). The results were astonishing. In just five months, that pair of flies would result in 191,010,000,000,000,000,000 family members—enough to cover the entire surface of the earth, several meters deep. So when considering your War on Flies, pay particular attention to their breeding grounds. Flies like to breed in moist, dark areas, ideally surrounded by trash or manure. By picking up trash, cleaning up manure, and taking steps to control mud, you’ll minimize their ability to reproduce.

Question 6: Answer B

Flies have compound eyes, made up of thousands of tiny individual lenses called ommatadia. This provides a very wide field of vision. A fly can see 360 degrees around his body at all times. Why is this important for your War on Flies? No matter the direction, flies can see you coming when you try to swat them. Add to this their lightning-fast reflexes (they see you coming and make a decision about which way to jump within 100 milliseconds of when you first move), and it’s easy to understand why it’s hard to kill a fly. If you want to be successful, you must plan ahead. Researchers studying fly reactions suggest planning which way a fly is most likely jump ahead of time (often backward) and swat accordingly.

Question 7: Answer C

A fly sucks up his food in liquid form through a proboscis, a tubular extension of the mouth similar to a straw. So how does he feed on solids? He uses a combination of saliva and stomach contents (“fly vomit”) to liquefy the surface so he can slurp it up. Disgusting, right? This fun fact might not help you wage your War on Flies, but it should provide plenty of motivation for keeping them away. And what about the flies that bite, such as deer flies and horse flies? Biting flies are typically blood feeders—they bite to gain access to a liquid blood meal. These bites are not only painful; blood-feeding flies are particularly dangerous as they’re most likely to spread serious diseases such as equine infectious anemia.

Question 8: Answer B

Flies are incredibly agile and maneuverable. They can not only hover and fly in all directions, but also jump backward when they perceive a threat. They even have small “rudders” next to their wings (called “halteres”) that help them to stay oriented when performing these acrobatics. And while it may seem that flies travel completely randomly, scientists have shown that flies’ flight patterns aren’t random at all. In fact, the typical flight pattern involves repeating straight lines and 90-degree turns that allow them to locate the source of odors they’re attracted to as potential food sources. The fact that this pattern seems random to observers gives the fly a big advantage when it comes to avoiding predators. Given their incredible agility and lightning-fast reflexes, it’s no wonder pesky flies are such formidable enemies.

Question 9: Answer A

Fly repellants can be effective…or not. Studies have shown that resistance to insecticides used for controlling flies is highly variable depending on geographic location and the specific populations of flies. That makes efficacy very hard to predict. Does that mean that fly sprays are completely worthless? Absolutely not. But trial-and-error is probably the most effective strategy to help you determine if a fly repellent is working for your horse. And be aware: A fly spray that works great at home might be less effective when you’re away from home, due to location-based resistance. Most importantly, the variable efficacy of fly repellants points out the need to have multiple weapons available for your War on Flies. no matter how hard to you try to eliminate breeding grounds and control populations, where there are horses, there will be flies.

Question 10: Answer C

It may be hard to believe, but flies actually have quite a bit to offer the world—starting with their disgusting eating habits. They not only “vomit” on their food to encourage decay, they follow up by eating it. And when they lay their eggs in piles of trash or manure, those eggs hatch into maggots that help to further break down decaying matter. In fact, maggots have seen a resurgence in popularity as a medical “device” that can be used to help debride infected wounds and encourage healing. Flies have other benefits as well. They do participate in pollination, and they feed on other pests like aphids that can infect the roses in your garden. Finally, flies are very low on the food chain, and provide nutrients for other important species such as birds, bats, and fish.

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