Introducing: The Botfly
What does a botfly look like?
The adult horse botfly is a brown, hairy fly with only one pair of wings and a body size of about 2 cm. In summer, we often see and hear adult botflies buzzing around horses. They strongly resemble bees and are often mistaken for horseflies.
How does an infection occur?
Female botflies lay their yellow eggs on the horse’s forelegs. Each fly lays around 1000 eggs. The horse licks up the eggs. The larvae hatch in the mouth and penetrate the oral mucosa. After a few weeks, the larvae move to the stomach, where they attach to the stomach wall and remain throughout the winter.
In late spring, the larvae detach from the stomach wall and leave the body through the manure. They then burrow into the ground, and after several molts, the adult fly emerges and the cycle begins again.
Can botfly eggs be found through fecal testing?
No, botfly larvae cannot be detected through fecal testing because the eggs are laid on the outside of the horse. We therefore recommend deworming preventively once a year, after the first frost. Are you a Worm&Co customer? Then relax — we’ll email you when it’s the best time to administer the end-of-year deworming.
Why only treat after the first frost?
The first frost kills off the free-living adult botflies, which eliminates the risk of reinfection after treatment.
Symptoms of botfly larvae
Horses carrying a botfly infection can become seriously ill. Symptoms include inflammation in the mouth, tongue, and stomach (gastric ulcers), reduced appetite leading to weight loss and lethargy. Severe infestations may also cause anaemia, loose stool, and in the worst cases, colic.
Preventing infection
What can you do to prevent or reduce infection? It is important to remove the eggs before the horse licks them up. Special knives and grooming stones are available (Horsefitshop). If this doesn’t work, you can wash the horse with lukewarm water and vinegar to make the eggs easier to remove.
Should I treat for botfly larvae every year?
We advise treating once a year, but there are situations where preventive treatment may not be necessary. For example, horses that have carried few or no eggs, or horses already treated earlier in the season. The most important thing is to use common sense and closely monitor your horse’s health.
If you have any questions or concerns, feel free to contact us.
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