Control of Insect and Related Pests of Livestock and Poultry in British Columbia

Horn Fly

Description of Injurious Stages and Damage

Horn flies are small, greyish flies, about one-half the size of a house fly, which cluster on shoulders, sides and belly, or around the base of the horns of cattle. They remain on the cattle day and night, indoors or out, feeding on their blood, resulting in annoyance, loss of weight, and decreased milk production of dairy cattle. Both sexes feed along the undersides of their hosts causing sores that gradually enlarge with continual attack year after year. Calves less than 5 to 6 months old are not attacked.

Summary of Life History

Adult females dart from their resting place on the cattle to lay their eggs in fresh cattle droppings. The maggots develop very quickly in the manure, and a life cycle may be completed in 2 weeks, resulting in several generations per season. Populations usually peak in late July and August. Horn flies overwinter as pupae or larvae under manure pats. They will not breed in feedlots. Additional information on biology and control of horn flies is presented in "Control of Horn Flies" (BCMAFF Pest Control Note 93-05).

*Horn fly resistance to pyrethroid-impregnated ear tags is becoming widespread in range pastures. Refer to "Management of Horn Fly Resistance to Insecticidal Ear Tags" (BCMAFF Pest Control Note 93-02), for information on preventing or managing resistance.

Control Recommendations

Beef and dairy cattle - insecticidal ear tags containing a synthetic pyrethroid (permethrin, fenvalerate, flucythrinate, or cypermethrin), a combination of pyrethroid and organophosphate (cypermethrin and diazinon), an organophosphate (tetrachlorvinphos or diazinon), or ear tag tape (permethrin); ready-to-use pour-on (1% cyfluthrin, eprinomectin,1% and 5% permethrin); whole-body spray (0.5% carbaryl or 0.0125% permethrin); dust bag (1% coumaphos); backrubbers containing 2% malathion.

Note: Do not apply ivermectin pour-on to dairy cattle within 2 months of calving.