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Bots (e.g. Gasterophilus intestinalis)

Infestation with bots results in digestive upset and reduced appetite.2 This is because bot flies lay the eggs on the horse’s leg hair or under the jaw, and when the larvae hatch, they find their way to the horse’s tongue and mouth. Once swallowed, the larvae attach to the stomach lining, causing symptoms – in fact, a heavy infestation can result in stomach ulcers or ruptures.1

When the larvae are passed out in the dung, they develop in the dung, resulting in an adult fly, ready to reinfest nearby horses.1


  1. Queensland Government Department of Agriculture, Fisheries and Forestry. Worms in horses, January 2012.
  2. Robinson S. Worm control in horses. PrimeFact 976, February 2010. NSW Government Department of Industry and Investment.