Companion Animals

Bot Fly Control in Horses: Welfare and Management

Managing Gasterophilus infection to protect horse gut health and welfare.

Key Facts

Horse bot flies lay eggs on legs, faces, and lips — larvae are ingested during grooming
Larvae attach to the stomach lining and can cause ulceration and obstruction
Treatment with ivermectin or moxidectin in late autumn removes larvae effectively
Bot fly season runs from late summer to first frost — eggs should be removed regularly

Welfare Considerations

Bot fly larvae cause gastric irritation and ulceration in affected horses. High larval burdens can cause colic and peritonitis. Welfare-focused control removes eggs from coat during fly season using a bot knife or fine-toothed comb, and treats all horses with macrocyclic lactone anthelmintic after the first frost to kill larvae before they cause significant damage.

What You Can Do

Remove bot fly eggs from legs and coat regularly during fly season
Treat all horses with ivermectin after first frost to kill larvae
Include bot fly larva control in your annual worm management programme