Horse Side Vet Guide ®

Equine Health Resource

Bot Eggs, Yellow-White Flecks on Hair or Skin

Code Green - Contact Your Vet to Obtain Useful Advice & Resources

Code Green - Contact Your Vet to Obtain Useful Advice & Resources

    In the fall, in the Northern Hemisphere, whitish-yellow flecks commonly appear on the chest, belly and upper front limbs of horses. These flecks are eggs laid by the Bot Fly, a bee-like insect whose life cycle requires the horse as a host. These eggs contain a substance irritating to the skin, and horses often bite at them.

    When swallowed, the larvae attach to and live on the lining of a horse’s stomach. Vets often see these larvae when performing endoscopy on horses for stomach ulcers. They are orange to red grubs about 3cm in length.

    Bot flies themselves are common and can be highly annoying, sometimes causing horses to stampede but they are not harmful otherwise. You will see them repeatedly depositing their eggs on the skin with their long ovipositor.


    Recognize that bots generally do not cause horses much harm and so it is not necessary to completely eliminate them. The eggs are difficult to remove but can be scraped off with a specially shaped bot egg knife or combed out to reduce the number a horse ingests. Soaking the affected hair in hot water may help to loosen the eggs.

    In late fall, after a few hard freezes the adult bot fly is inactive. This is a good time to try to remove the eggs. Talk to your vet about the necessity to de-worm your horse in the winter with ivermectin or moxidectin to kill the larval stages in your horse’s stomach. Talk to your vet if you have any additional questions or concerns.


    Your vet considers bot management as part of a good general parasite control program.

    Identify or Rule-Out Possible CausesDIAGNOSES

    Tests to PerformDIAGNOSTICS

    POSSIBLE TREATMENTS or TherapiesTo Lessen or Resolve the Sign

    Helpful Terms & Topics in HSVGWritten, Reviewed or Shared by Experts in Equine Health

    Author: Doug Thal DVM Dipl. ABVP


    We're not around right now. But you can send us an email and we'll get back to you, asap.