I have a little story to tell you. But it isn't pretty. The main character, a tiny honeybee, sort of a mouthless fly, is out to get a literal ride on your horse or donkey. Only she won't stay long. But she'll leave her calling card - between 150 - 1000 gray to yellow eggs on your horse before she flies off to die.
At first those eggs will just hitchhike on your horse's legs, flank or shoulders and even around the head, depending on the type. But their goal is to get inside via the mouth, muzzle or eyes. All it takes is for your horse to feel itchy there, and rub or lick the eggs, and bingo! they are stimulated to hatch and crawl upwards or just end up in the mouth through the licking process.
Now you might not want to finish this little horror story if you are a bit of the queasy sort. Just the idea of a bot parasite in the mouth, even if it's a horse's mouth, makes me gag. But to think they burrow in the gums and under the tongue for a month makes me shudder. And don't show me a picture of someone kissing their horse!
After they do their little stint in the mouth, they release themselves to be swallowed where they can feast on the deeper insides of your dear friend for most of the year until they release again to be dropped in the apple pickin' pile to hatch the little fly fiend that started the whole thing.
But there is a hero in this dark story. The worming drug ivermectin safely and effectively minimizes the damage this parasite can do to your horse's nutrition and gut (and if you are really queasy, you don't want me to go into detail on the damage it can do!). It won't actually kill the worm, but it will force the second and third stage sucker to release its hold before it is matured. That way the worm is safely passed out of your horse from the opposite end it went in.
So here's the key question...when should you worm your horse to make sure you catch the bots before too much damage is done? A good idea is to worm them in the early summer, one month after you see the bots dive-bombing your horse, or actually see them on them. That way your wormer catches them soon after they are out of the mouth and in the second stage in the body. It’s also a good idea to use a boticide (ivermectin or moxidectin) again in the fall to go into the winter with as clean insides as possible before the winter months. A lot of people like to buy a combination wormer with ivermectin or moxidectin and praziquantel, to knock out the tapeworms at the same time as the bots.
Speaking of a lighter bot parasite load, there is a way to prevent some infection of your horse: scrape the eggs off early in the season from their attached state on the coat. A bot knife, works well as it's rounded to get around the legs. Just be sure you don't wipe them on the ground where they can be ingested from there. Use a throw-away tarp underneath your horse or scrape the larva off while your horse is standing on gravel. You may want to wear protective gloves when dealing with these parasites.
Anyway, the moral of the little story is: Bots are BAD, but ivermection is GOOD ...especially at Valley Vet prices! Ellen