Battling bot flies in horses…did you know they can infect humans?

The bot flies are here…again. I ran into my first bot fly eggs this spring in Texas, which I found unusual because I am accustom to seeing them in late summer in Ohio and Maine. In some warmer states, such as Florida, it is possible for bot flies to live year round…I will chalk that up to one down side to a lack of winter.

Bot flies are amazingly good at laying their eggs, each female will lay 150-500 eggs. While riding the other day I noticed my friends horse was covered with bot eggs. She allowed me to video the eggs before she removed them. In the video you will notice that the bot fly lays the eggs in all the places where a horse will frequently scratch, rub, or swat flies away from.  The eggs hatch when heat, moisture and carbon dioxide are present. I found this gross fact (below) and can’t decide if I should try it or not…

Researchers have witnessed this phenomenon using a microscope. “If you breathe on them, they immediately hatch,” says Jack Campbell, PhD, veterinary entomologist at University of Nebraska’s West Central Research and Extension Center. “I’ve had them in a petri dish, getting ready to photograph them, and if you happen to breathe on them, you can see the egg opening up as they come out the end of it.” click here for full article

The unfortunate horse will ingest the eggs, which will hatch in the mouth. The larva spend the winter months in the stomach and then pass through the manure. The adults emerge, lay more eggs and the cycle repeats.

It is important to remove the eggs as soon as possible to reduce the chance of the horse ingesting them but do keep a few things in mind.

  • First, as another friend pointed out “It makes no sense to scrap the eggs off in an area where your horse eats like the stall or as you are hand grazing them…”
  • This same friend also pointed out the fact that there have been cases of humans becoming infected…YUCK! I didn’t want to believe her but a quick google search showed me this article complete with a photo of a horse bot fly larva in a human eye. So remember…wash your hands and don’t rub your eyes!

There are many tools available for removing the bot eggs. I don’t suggest your finger nail after reading the above mentioned fact… My favorite tool, so far it the bot fly knife. My second favorite is the grooming block. What is your favorite tool?

Deworming is also important, ivermectin and moxidectin are both effective although ivermectin is more effective.

This link will take you to the most complete article I found on bots.


  1. SarahJane Dyer on September 24, 2014 at 7:43 pm

    I’ve never seen them in MA but not sure if they go up this far north

    • Jill Pflugheber on September 26, 2014 at 10:39 am

      Sarah–we have bazillions of them in far northern NY, so I’m sure you have them in MA. They seem to be especially obnoxious this year.

  2. Robert J. Fisher on September 24, 2014 at 7:38 pm

    Any truth to the rumour that wiping with a diesel fuel cloth will ki
    ll the eggs before removal?

    • Stacy on September 25, 2014 at 4:47 pm

      I have been removing them while they are in a non-grazing area, like the driveway. If they are not ingested they won’t live. I’m not comfortable wiping diesel fuel on my horse but maybe some of the other less aggressive things (Vaseline, etc) or even bug spray.

  3. Kathi on September 24, 2014 at 4:18 pm


  4. firnhyde on September 24, 2014 at 11:05 am

    We have the blasted things all the way out in Africa, too. I’m sure the adult flies must bite or sting painfully – the horses are much more afraid of them than they are of bees.

  5. saddlequest on September 24, 2014 at 10:20 am

    Very interesting information. I had been taught that bot eggs do not hatch until after the first freeze. Now, I will have to be extra diligent (and not touch my eyes!) on a daily basis. Thanks Stacy!

  6. Tammy Wynn on September 24, 2014 at 9:54 am

    I have found the best tool that works for me is a nit comb. The kind you get in in the lice or over set from the drug store. Cracked hooves and bot eggs are my worst pet peeves!

  7. Werner on September 24, 2014 at 9:49 am

    A cloth and warm water and the eggs will come right off. Same principle as breathing on them. warm them up and they release.

  8. Melita Gard on September 24, 2014 at 7:47 am

    I think they are everywhere even here in the land down under.

  9. Linda on September 23, 2014 at 11:21 pm

    You might take them off but they are still able to be breathed in where they lie, So Every day I wipe the legs with kerosene that kills the eggs so if i miss one or two at least there dead

  10. cowgirlmichaela on September 23, 2014 at 8:31 pm

    I used a razor blade and it was perfect! Are there any states where bots don’t live?

  11. ferg05 on September 23, 2014 at 7:55 pm

    We adopted a horse from Texas and had her transferred to AZ in March of this year. Sadly she came covered, her legs and belly in bot fly eggs. I’ve never actually seen bot flies or their eggs, but from pictures and reading it was clear what she had. It took us 4 days of scraping and cutting to get them all off and then two coarses of ivermectin. Our Vet did tell us that in some parts of our County there are bot flies, but in our neck of the woods we don’t see them. Not an experience I care to repeat! Oh and we tried all kinds of products and the best for us was a bot knife and scissors and cut the hair away from the body.

  12. Naomi P on September 23, 2014 at 6:36 pm

    I use a mane thinning comb. I comb with the direction of the hair, or from a diagonal while putting pressure on the comb at the same time. This causes the hair to bend towards the comb and the eggs are scraped off of the hair. It works great! I always try to also put a little extra fly spray on my horses legs around bot season.

  13. Mathilde on September 23, 2014 at 6:28 pm

    Ive always found bot knives to be quite handy.

  14. Kaylene Wilson on September 23, 2014 at 6:17 pm

    We use a pumice stone, just the cheap ones you get at the dollar stores.

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