Bot fly eggs are mainly laid around a horse’s eyes, mouth, nose and legs. The eggs are laid by the female bot fly, who can lay up to 1000 eggs.

Many horses become irritated with the bot fly as she lays her eggs, which can disrupt a horses eating habits and behaviour, as well as distract it whilst being ridden.

The bot eggs are only a small part of the lifecycle.

Once the eggs are laid, they hatch approximately seven days later, after being triggered by moisture from the skin or horse’s mouth.

When the horse licks or rubs its mouth on the larvae, they enter the horses mouth.

One species of larvae will actually migrate through the skin into the horse’s mouth.

After three weeks in the mouth, the larvae migrate to the lining of the horses stomach, where they remain for approximately ten months, prior to detaching and passing out in the horses faeces.

During this time damage and irritation occurs to the stomach lining, which can cause ulcers to develop. 

Once the bot fly larvae is excreted, it burrows into the ground to mature, emerging in three to 10 weeks as a fly ready to continue the cycle.

Thankfully, the first frost will kill the female bot flies, although it is important for owners to worm all of their horses with a worm drench or paste which includes a boticide, as well as remove as many eggs as possible to reduce the effect on your horse.

There are various methods of removal available. Speak to your vet about how to manage it.