Horn Fly

Haematobia irritans (family Muscidae) is a small biting fly, 3-4 mm long — roughly half the size of a house fly — dark grey with a rigid, forward-projecting bayonet-like proboscis and short, stout palps. Females leave the host only briefly to lay eggs in very fresh cattle dung pats, depositing 20-24 eggs per batch and several hundred over a lifetime. Eggs hatch in under 24 hours, larvae complete three instars within the dung in 4-8 days, and pupation occurs under or beside the pat. The complete cycle can take only 10-14 days in warm weather, producing explosive seasonal populations; the species overwinters as diapausing pupae in soil beneath pats.

Both sexes are obligate blood feeders and remain on the host almost continuously, taking 20-40 blood meals per day, typically clustered on the shoulders, back, and belly with heads pointed downward. Their persistent feeding causes irritation, blood loss, reduced grazing time, and measurable weight-gain and milk-production losses, and they mechanically transmit Stephanofilaria and contribute to bovine mastitis pathogen spread. Flies leave the host mainly to oviposit and briefly during extreme heat, resting on the shaded underside of the animal. Dispersal between herds occurs over several kilometers.