5 Things to Know About Bot Flies

Annoying Insects Are Coming!

The first time I saw a bot fly, I thought it was a bee. I was riding up near the Idaho border on a late summer day, when suddenly my horse got very irritated. He pinned his ears and started kicking out. I dismounted and then I saw it buzzing around his underbelly. I watched as the bee-esque insect dive-bombed my horse’s legs. It looked like it was stinging him, but it wasn’t. Then I saw the tiny eggs. A bot fly!

These annoying insects love horses, but the feeling is not mutual. In addition to being a major irritant, bot flies have a singular mission: to glue their tiny eggs to the body hairs of equines in the hopes that they will ingest them. Add bot flies to the laundry list of gross things to worry about when it comes to horse ownership. Here are 5 things you should know about bot flies:

1Bot flies originated in Africa.

Today, there are nine different species around the world that primarily affect horses and donkeys. Three species are found in North America.

2Adult bot flies are yellow and black.

They resemble honey bees, but only have one pair of wings. They are about ¾ inch in length. They have nonfunctional mouthparts and do not feed or bite.

3A female bot fly can deposit between 150 to 500 eggs on a horse!

She lays the eggs directly on single hairs, typically on the horse’s legs, abdomen, flanks, and shoulders.The eggs are approximately 0.05 inches (0.127 cm) in length and yellowish in color.

4The eggs develop into larvae when the horse licks or bites at the attached eggs.

The larvae are ingested and bury themselves in the tongue, gums, or lining of the mouth. Then they move to the stomach where they attach themselves to the lining. There they remain for nine to 12 months.

5Once they have matured, the larvae detach and pass from the horse’s body in feces.

The larvae burrow into the manure where they pupate for one to two month’s before emerging as an adult bot fly to begin the cycle again.

An adult female bot fly will drive most equines crazy with its attempts to deposit eggs. So, how to protect your horse? Thoroughly check your horse every day for eggs. They can be scraped off with a bot fly knife, a sharp edged tool, or sandpaper. Clean up manure and transport it away from horses. Use fly spray during the peak egg laying season. Deworm your horse if you suspect he ingested eggs. Commercial fecal tests do not detect bot flies!

Also be sure to always wear gloves when removing bot fly eggs. Do not rub your eyes and wash your hands immediately afterward. Though it is very rare, there have been cases of horse bot flies choosing humans as a host. Luckily, they are unable to develop in humans so the small larvae will die off within a few days. Note however, there is a different species of bot fly that does target humans. But, it is not generally found in the U.S.

Story by Samantha Szesciorka