Heel flies

Definition

Common name for warble flies of the genus Hypoderma (family Oestridae), large robust flies whose adults harass cattle and deer by darting at the legs—especially the heels—causing animals to panic and run (gadding). The females later attach eggs to hairs, and the larvae develop as subcutaneous parasites, migrating through tissues and forming warble-like swellings (grubs) on the back before emerging. The term emphasizes the adult's irritating behavior rather than the parasitic larval stage.

Etymology

From the adult flies' habit of striking at the heels of cattle, provoking the characteristic 'gadding' flight response.

Example

Ranchers in northern climates often treat cattle in spring to prevent heel fly larvae from tunneling through the esophageal wall and diaphragm before reaching the back.

Synonyms

• Warble flies
• bomb flies
• gadflies

Related Terms

• Hypoderma
• Oestridae
• myiasis
• Cattle grub
• gadding
• hypodermosis
• warble

Usage Notes

Primarily a livestock/veterinary term; 'warble fly' is more common in European usage, while 'heel fly' predominates in North American ranching contexts. The larvae are never called heel flies—those are specifically 'cattle grubs' or 'wolves.' The common name 'gadfly' overlaps with non-parasitic horse flies (Tabanidae), creating occasional ambiguity.