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bots eggsBot eggs

The bot (stomach worm) is not a worm but the larvae of Gasterophilus flies.

The adult horse bot fly emerges a during the summer or fall season. After the fly emerges from the pupa, it quickly finds a mate, lays the eggs on the horse's coat and, on grooming, the eggs make their way to the mouth where they hatch in mouth as larvae.

Over winter the larvae burrow into the stomach lining (where they spend 8-10 months) and are then passed out via the faeces and will hatch in the summer.

Significant trauma and ulceration of the stomach can occur following infection.

Disease is also caused by the larvae in mouth. Larvae here create borrowing holes, which in turn become infected. The 3rd stage larvae are passed in the faeces and over winters to develop the following summer.

Infected horses can often show no signs, which is why treatment should be given over the winter months to kill them.


bots-gasterophilus fly larvaeBots fly larvaePhoto kindly provided by University of Liverpool Diagnosteq Lab

Which Actives Treat Bots (Stomach Worms)?

Ivermectin Moxidectin Ivermectin / Praziquantel Moxidectin / Praziquantel
Pyrantel Praziquantel Fenbendazole Mebendazole


Bimeda Equine is proud to promote best practice targeted worming regimes, to help protect both today’s horses and future generations.

To find out more about best targeted worming regimes, visit our Best Practice Advice section.

To view and download our materials, such as our Horse Owner’s Guide To Worming, visit out Library Section.

Contact Us - UK

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Unit 2, Bryn Cefni Industrial Park,
Llangefni, Anglesey, Wales LL77 7XA
Phone: +44 (0) 1248 725400