Bots in Horses

Signs of Bots in my Horse

Bot eggs on the hair of horses is the major sign your horse has bots.  You may also see a little fly that looks similar to a honey bee flying around certain areas of your horses body especially knees, hocks, tail head, and throat latch.

On rare occasions, you may see the actual bot larvae in the stool of your horse especially after deworming with ivermectin or moxidectin.  Fecal egg counts do not contain bot eggs as they are seen on the horses’ hair.

These larva attach to the lining of the stomach and cause a very small ulcer. When there is a heavy infection these ulcers may join to form a large ulcer.

There are indications that if the ulcer is large enough it may cause colic.

Horsemen’s Laboratory recommends deworming for bots in late fall or early winter.

What are Bots?


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Bots (gasterophilus) are the larvae of botflies. The yellow eggs are laid on the hairs on the front part of the horse, within reach of his tongue.

The eggs hatch in 10 to 14 days and the horse will lick them off his coat and transfer them to his mouth, where the larvae burrow into the mucous membranes of the lips and gums.

Bots infect horses in many parts of the country. They have a very interesting life cycle with the adults resembling a honeybee. The larva in the stomach look similar to many free-living grubs.

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Specimen Photos/Illustrations