Hypoderma Bovis spp Infestation

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Diseases and conditions image EquiMed

Also Known As

Warbles, Cattle Grubs


Hypoderma Bovis ssp infestation, also known as warbles, is an atypical infestation of parasitic larvae under the skin of the horse, usually along the topline of the back and rump. Warbles most often affects cattle, but occasionally horses, sheep, and humans become infested with the parasitic larvae.

Mature hypoderma flies lay eggs on the skin of the horse. The eggs hatch and the grubs penetrate directly through the skin, migrating through the fat beneath the skin along the spinal column. Grubs typically lodge in the subcutaneous fat along the back, forming painful lumps under the skin. Occasionally, grubs can migrate as far as the brain, causing severe and fatal neurological disease.


  • Rash
  • Discrete swellings along the back and saddle area
  • Nodules characterized by a small breathing hole for grub
  • Lack of limb coordination
  • Muscle weakness
  • Paralysis
  • Hemorrhage
  • Tissue damage


Warbles is caused by the aberrant (atypical) infestation of the grub of the cattle fly Hypoderma bovis.


The best prevention is to make sure horses are not exposed to cattle and cattle flies which are the primary source for warbles infestation in horses.

Control of the grubs in cattle with macrocyclic lactone (ivermectin, epimectrin, moxidectin) parasiticides and manure management will help reduce the risk for horses. Early stages of infestation can be controlled and/or prevented through the use of macrocyclic lactone dewormers.


While early stages of larval infestation may be treated with systemic dewormers, once the grub is more mature there is concern that killing the grub can release toxins which cause an anaphylactic or severe allergic response in the horse. Mature grubs should be surgically removed, intact and alive, by a veterinarian.

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EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.