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Gasterophilus intestinalis, Trawscoed, North Wales, Aug 2015 (20134961243).jpg
G. intestinalis
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Diptera
Family: Oestridae
Subfamily: Gasterophilinae
Genus: Gasterophilus
Leach, 1817

Gastrus Meigen, 1824

Gasterophilus is a genus of parasitic flies in the family Oestridae which includes the horse botfly. They lay eggs on horses, caribou, donkeys, and similar animals, usually equines. The eggs are laid depending on the species of gasterophilus. There are two species - Gasterophilus nasalis, and gasterophilus intestinalis. Nasalis lay eggs around the mouth, eyes, nose, and chin. Intestinalis lay eggs around the lower legs, and shoulders.[1] The eggs hatch by licking, moisture or humidity. The gasterophilus intestinalis then travel to the mouth where larvae are hatched and travel into the intestines. The gasterophilus nasalis travel to the sinus cavities and/or the brain. Gasterophilus is laid by the bot fly which looks like a bumble bee, which hovers around the ground. These can be managed and maintain a lower amount by a de-worming schedule and removing the eggs with a bot comb or a grooming block. Intestinal bots in large numbers can cause gastrointestinal problems with animals.

There are exceptional cases of human babies infected by these flies.[2]


Gasterophilus are medium to large flies and are between 10-20mm long. They look similar to drone bumble bees with clear wings with brown patches, and produce creamy-white eggs, around 1-2mm in length. The adults have non-functional mouthparts so cannot feed.

G. haemorrhoidalis and G. nasalis have two rows of spikes on the ventral surface of the larval segments. G. intestinalis have mouth parts that are not uniformly curved dorsally and the body spikes present have blunt ended tips.[3]



  1. ^ "Gasterophilus spp in Horses". March 2012. 
  2. ^ Royce, L. A., Rossignol, P. A., M. L. Kubitz, AND F. Randell Burton 1999. RECOVERY OF A SECOND INSTAR GASTEROPHILUS LARVA IN A HUMAN INFANT: A CASE REPORT. Am. J. Trop. Med. Hyg., 60(3), 1999, pp. 403–404 [1]
  3. ^ "Gasterophilus spp". WikiVet. 

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