By: Katie Jones, CVT

Many of us are familiar with the yellow “seeds” that appear on our horses’ legs during summer months as bot eggs, but what exactly can we do to prevent these recurring parasites each year?

bot-eggsThere are three different types of botflies. The first is considered the common horse bot (Gastrophilus intestinalis); they lay their eggs on the horse’s body and are ingested through self grooming. The second is the throat bot (Gastrophilus nasalis), they lay their eggs on the horse’s neck and beneath the jaw. The larvae from these eggs then travel from the neck to the mouth. The third and final type is the nose bot (Gastrophilus haemorrhoidalis). This type of bot is the rarest type and they lay their eggs around the lips. Once the bot larvae are in the horse’s mouth they remain there for around four weeks before traveling into the stomach. When the larvae enter the stomach they attach to the division between the glandular and non-glandular portions of the stomach (the Margo Plicatus). The larvae have hooks in their mouths that allow them to attach to this division for eight to ten months, or until mature.   Once the larvae have reached this stage, they release themselves from the lining of the stomach and are passed in the horses feces. When they finally reach the environment, they burrow into the ground until they mature into adult flies. This lifecycle takes about a full calendar year; once the adult botfly emerges from the ground the cycle starts again.

There are several symptoms a horse possesses if they have been exposed to bots. Bot botseggs on the body of the horse appear as clusters of orange and yellow dots on their head, belly, and legs. Due to these eggs a horse can be found licking at their stomach and legs, biting or rubbing their mouth (to try and relieve irritation), with ulcers in and around their mouth, or appear colicky. When the number of larvae in the stomach becomes overwhelmingly large a blockage can form, as well as, ulcers along the stomach lining.   Visualization of the bot eggs and larvae is the main diagnosis. Once the bot larvae attach in the stomach they can be seen by gastroscopy.

To decrease a horse’s exposure, it is recommended to promptly remove any eggs found in the hair. This will minimize and even disrupt the bot’s life cycle. Using fly spray and fly control practices in barns during summer months will also help decrease chance of exposure.   The best way to prevent bot larvae in the horse’s stomach is by practicing a good deworming schedule. The recommendation is to give a deworming product containing Ivermectin, preferably after the first frost in the fall.

Botflies are common in the Midwest but with good management, horses can be treated and the risk of exposure can be decreased. If you have concerns regarding bots, make sure to connect with your veterinarian to discuss what your horses’ risks are.