Warble or bot flies

Definition

A vernacular grouping of robust, beelike flies whose larvae are obligate endoparasites of mammals, typically developing in subcutaneous or gastrointestinal tissues and causing characteristic swellings (warbles) or internal myiasis. The group spans several families—most notably Oestridae (including Hypodermatinae, the classic cattle grubs) and Gasterophilidae (horse bot flies)—united by larval lifestyle rather than by a single clade. Adults are often non-feeding, with reduced mouthparts, and deposit eggs directly on hosts or on vegetation the host will contact.

Etymology

Warble from Middle English warblen, to sing with trills, perhaps from the ripple-like swelling; bot from Middle English, akin to Gaelic boiteag, maggot.

Example

First-instar larvae of the cattle warble fly Hypoderma lineatum migrate through the esophageal wall, then settle in the back to form breathing warbles before pupating; horse bot fly Gasterophilus intestinalis larvae attach to the stomach lining, causing ulceration.

Synonyms

• oestrids
• hypodermatids
• gasterophilids

Related Terms

• myiasis
• obligate parasite
• Endoparasite
• hypodermis
• cutaneous larva migrans
• screwworm fly
• tumbu fly

Usage Notes

Warble fly traditionally refers to Hypodermatinae and related Oestridae causing subcutaneous swellings; bot fly more broadly covers Gasterophilidae and sometimes North American Cuterebridae (rodent bots). Specialists increasingly restrict 'bot fly' to Gasterophilidae and use 'warble fly' for Hypodermatinae, though lay usage overlaps. Not to be confused with blow flies (Calliphoridae), which cause secondary myiasis.