Horn Flies

Barry Whitworth, DVM & Justin Talley Ph.D.

Horn flies, which are about ½ the size of a house fly, spend most of their time on cattle. 

The scientific name for horn flies is Haematobia irritans.  As the name implies, the flies are very irritating to cattle.  Physiological changes occur in cattle with horn fly infestations such as increase in heart rates, increase in respiration rates, increase in rectal temperatures, and increase in water consumption.  If the flies are not controlled, the cattle waste energy licking their backs, twitching their flanks, switching their tails, and stomping their feet.  Spending all this energy on combating this pest and less time eating results in weight loss and lower milk production.  The economic loss to producers can be very high.  The horn fly is a costly parasite to the cattle industry with estimates of $1 billion in lost production.  In addition to lost production cost, producers spend an additional $60 million in horn fly control. 

The life cycle of the horn fly is simple.  Horn flies, which are about ½ the size of a house fly, spend most of their time on cattle.  Horn flies are distinguishable from other flies because they congregate with their heads pointed down.  They are usually seen in groups on the backs and shoulders of cattle.  They migrate to the belly when it is hot.  The flies may take up to 40 blood meals a day.  The female fly must have a blood meal to reproduce.  The only time the female leaves the cow is to lay eggs in a fresh manure pile.  The eggs will hatch, and the larvae will live on the material in the manure pile.  In a few days the larvae move into the soil to pupate and emerge as adults.  The life cycle from egg to adult takes 2 to 4 weeks.  For a more detailed description of the horn fly life cycle go to http://livestockbugs.okstate.edu/horn-flies.

One of the most common method of controlling horn flies is the use of insecticides.  The insecticide comes in many forms such as an organophosphate, pyrethroid, pyrazole, and macrocyclic lactone which can be applied in a spray, pour-on, dust bag, back rubber, insecticide tags, breakable capsules from a modified paint gun, or oiler.  Insecticide impregnated ear tags are a commonly used method to control horn flies.  Since the tags will protect for a limited amount of time, producers should not place the tags in the animal until flies become a problem.  Ear tags should not be left in the animal year-round.  It is important to remove the tags by fall to reduce resistance problems.  Since resistance is a problem with fly tags, producers need to rotate classes of insecticides every year.  Recent research has shown that once pyrethroid resistance is established in horn fly populations then it remains in the subsequent populations for up to 3 years without any pyrethroid use.  For more information about rotating fly tags go to http://livestockbugs.okstate.edu/horn-flies/insecticide-ear-tags.  When using any insecticide, dairy producers should read and follow label directions especially since not all products may be used in dairy cattle.

Other control methods of fly control are larvicides, non-insecticidal, and biological.  Larvicides such as Insect Growth Regulators (IRG) are fed to cows in a feed or mineral supplement.  The IGR passes through the animal and kills the immature horn fly.  An example of a non-insecticidal control method is the use of an insect trap.  They work when a cow walks through the trap and the fly attaches to a sticky strip.  Another type of a trap that was specifically designed for dairies and horn flies is the CowVac which sucks the horn flies off the animals which is good for those dairies in a certified organic program (https://spalding-labs.com/products/fly_control_products/cow_vac/default.aspx ).  Traps can destroy large numbers of horn flies quickly.  Biological methods of control use some type of predator insect such as dung beetles which eat the immature stages of the fly such as eggs.  Producers should never forget how important sanitation is in controlling horn flies.  Simply breaking up fecal piles will help because this allows the manure to dry out.  Dry manure is not a favorable environment for development of the immature horn fly.  The best horn fly control programs will take an integrated pest management (IPM) approach using a variety of control methods for long-term success. 

Horn flies are irritating to beef and dairy cattle and a costly nuisance for cattle producers.  For this reason, a strategy to control horn flies needs to be developed for the cattle operation.  Producers need to keep in mind that one control method will not be enough to keep horn flies away.  Producers will need to use a variety of control methods to successfully manage horn flies for the long term.  If a producer would like more information about horn fly control, they need to visit with their local veterinarian or Oklahoma State University Cooperative Extension Agriculture Educator.