The larvae of the bot fly are known as bots. Being an insect, rather than a worm, they have a more complex body structure, and their development includes three or more larval moults followed by development into a pupa before emerging as the adult fly.

Bots are commonly recognised by the eggs deposited by the fly on the horse’s coat, often around the shoulders, upper foreleg and neck. The eggs look like tiny grains of rice, and are pale cream in colour. Manual removal of the eggs at this stage can be an effective aid in controlling this parasite. The eggs quickly develop into larvae which are either licked by the horse, or crawl to the horse’s mouth to be ingested.

Once inside the horse, the larvae take around
10-12 months to develop into adults. Treatment to control bot infections is required once annually, in late autumn/winter, after the frosts have killed off any surviving adults and before the larvae develop into adults in the spring.

Size/Appearance: The eggs are up to 2mm long, creamy white in colour; the larvae are up to 2cm long and are a reddish-orange colour, and the ‘buzzing’ adults are the size of a honey bee, and can be very irritating to a horse.

Location in Horse: Eggs found on horse’s coat, with larvae in the mouth and stomach.

Symptoms: Mild damage to the mouth and gums, as well as stomach ulcers.