HPIPM:Black Flies

Authors: Gregory Johnson and John B. Campbell (Retired)

Identification and Field Biology

Black flies are small (1/4" in length), powerful fliers, that are black to yellowish with an arched or “humpbacked” thorax. Due to the enlarged thorax, they are sometimes called "buffalo gnats." Most female black flies are blood feeders whereas both sexes feed on floral nectar or plant sap. About two-thirds of the black fly species feed on mammals and the other third are mainly bird feeders. Eggs are deposited in layers or irregular strings on the surface of objects that are kept moist by moving water or directly in the water. Larvae can be found attached to stones, branches, grass or other debris in swift-flowing water. They attach to the substrate by means of posterior suckers, which contain hooks. Most species possess mouth brushes, which are used to filter-feed on microorganisms from the water. The non-feeding pupal stage remains attached to underwater substrate. When the adult is ready to emerge, it expels air from its system which splits the pupal cuticle. The newly emerged adult rises to the surface in an air bubble. It then seeks a resting place to tan and harden.

Adult flies generally live three to four weeks. They are daytime feeders and usually attack thinly haired regions on the animal (around the eyes, in the ears, on the muzzle or belly). Black flies are exophilic (i.e., they will not enter buildings to feed or rest).

Animal Response and Economic Losses

There are no studies relating numbers of black flies to animal losses. Annoyance of livestock under attack is evident, particularly by those that feed in the ears. There bites are irritating and can result in lesions that can persit for days to months. When feeding is intense, scabbing can occur. Black flies are biological vectors of vesicular stomatitis and bovine onchocerciasis. Livestock deaths by exsanguination (bleeding out) have been reported during massive attaks. There have also been reports of cattle suffocating when inhaling large masses of black flies.

Chemical

Insecticides used as cattle sprays for other livestock insects may provide some reduction in black fly numbers. Insecticide sprays for use on cattle are listed below.

Insecticides Suggested for Treatment of Black Flies on Cattle:

Insecticide	Application Method	Application Rate	Restrictions and comments
Atroban 11% EC	Spray	11% permethrin	Spray to thoroughly wet animal. Repeat as needed every 10-14 days.
Brute	Pour-on	10% permethrin	Aids in control of black flies.
GardStar 40% EC	Spray	40% permethrin	Spray to thoroughly wet animal. Repeat as needed every 10-14 days.
Permethrin 1%	Pour-on	1% permethrin	Repeat as needed every 14 days.
Permectrin CDS	Pour-on	7.4% permethrin	Aids in control of black flies.
PYthon	Ear tag	10% zeta-cypermethrin	Aids in control of black flies.
Synergized De-Lice	Pour-on	1% permethrin	Aids in control of black flies

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.