Understanding the Effects of Flies on Cattle Production

by Dr. Steven Blesinger

Cattlemen spend countless dollars and hours on efforts to maintain and improve the productivity of their cattle. Some inputs are designed to promote performance while others are needed to reduce challenges. One of the most common and most expensive challenges producers, and their animals, face are flies. 

Flies are a constant irritant and performance drain on cattle whether on pasture or drylot. They take nutrients from the animal by the constant blood they can suck, produce high levels of stress with constant irritation and transmit a variety of diseases contributing to additional production, health and economic losses. 

Recent data (Taylor et al, 2012) estimate economic losses to the cattle industry exceeding $4.19 billion annually. This is equal to roughly $45.00 for every beef and dairy animal in the US. 

There is one very important fact that must be recognized when we discuss flies that affect cattle and cattle producers. We are not just talking about one species. There are approximately 16,000 species of flies in the US and over 120,000 species world-wide. Of these species four common types have been measured as the most problematic for cattle. 


Stable Flies 

A larger and more expensive threat are stable flies, Stomoxys calcitrans. Stable flies are actually a source of greater losses, an estimated $2.21 billion annually. Their feeding patterns are different with mouth parts that do not bite or pierce but actually rip the skin causing blood flow that is slower to clot. Once the blood starts to ooze out, they return and actually lick blood. The ripping process causes significant pain, greater than that caused by horn flies. Production or economic losses are caused by reductions in grazing and defense behaviors, such as foot stomping, head throwing, skin twitching, tail switching. Cattle seem to spend more time bedded down, primarily to protect their legs, which is the stable flies’ favorite part of the host. The economic threshold is only five flies per leg. Stable fly populations appear to have increased with feeding of large round hay bales as observed by Broce et al, 2005. The accumulations of hay and animal wastes around hay feeding areas are excellent substrates for the development of stable fly larvae. 


Horn Flies 

Horn flies, Haematobia irritans, is probably the most well-known. It is also the group many producers throw all flies into. But horn flies are not the biggest economic problem. It was previously mentioned that total fly losses in cattle were an estimated $4.19 billion. Economic losses attributed to horn flies are estimated at about $1 billion annually, just under 25% of the total. Horn flies will bite the animal with an individual fly feeding as many as 40 times per day. They have mount parts (proboscis) that are dagger-like and used to pierce the skin largely around the horns but also the head, neck and shoulders but they do not focus on a specific body location. Aside from blood loss (nutrient drain) other production or economic losses are from head swinging, tail switching, and skin twitching. The economic threshold is about 200 flies per animal. The horn fly’s only diet is blood. They only lay their eggs in cattle manure where the larvae will hatch and develop, using the manure as their food source. 


House Flies 

Another problem fly species is the common house fly, Musca domestica, causing economic losses of around $750 million. Organic matter, manure and waste are the main food sources. House flies do not have a proboscis, instead they have a spongy mouthpart. Economic losses due largely to nuisance or irritation. Additionally, houseflies are known to carry over 100 pathogens, including over 65 human and animal diseases, as well as internal parasites. Of concern to the cattle industry, Bovine Viral Diarrhea (BVD), Infectious Bovine Rhinotracheitis (IBR), E Coli, Moraxella bovis (Pinkeye), and mastitis organisms are included in the pathogens that can be transmitted by house flies that need to be considered. 


Face Flies 

Finally, face flies, Musca autumnalis, contribute to industry losses estimated at $230 million. Face flies gather around the face and muzzle of cattle. Their mouthparts are adapted for sponging up saliva, tears and mucus. Cattle are the primary host, although they will feed on any animal including humans. Females feed off on facial secretions to obtain protein for egg production. Irritation, damage and infection of the animal’s eyes are a common result. The feeding activity of face flies enhances the transmission of Moraxella bovis (Pinkeye), and Thelazia eye worms. Face flies predominantly stay within the proximity of the host (cattle). 100% of their eggs are laid in cattle manure. 

Take Away Messages 

Left uncontrolled, flies can be a source of significant economic losses on even the best managed cattle operations. Fly population management is critical to all cattle operations. 

It is important that fly problems are multi-species in nature. Horn flies are not the only problem or even the most significant. As part of the total estimated annual losses, horn flies are the cause of just under 25% of these losses while stable flies can drive a staggering 52.3%. House flies and face flies follow with 17.5% and 5.3% of losses respectively. Using the $45.00/head annual loss average, this means that losses by fly species will average: Horn Flies - $11.25, Stable Flies – $23.34, house flies - $7.88 and Face flies – $2.38 per head. 

A sound fly control program must target all the economically important fly species. Using a program that only targets one of these species, horn flies, still allows significant losses to the producer. Understanding this a broader spectrum fly control program is indicated.