The Flies Actually Costing Your Herd Money

The relentless challenge of controlling flies on cattle can frustrate even seasoned ranchers. Just as you think they’re under control, they return—buzzing around eyes, biting legs, and stressing your herd. You’re not alone in dealing with this. The real key to fly control isn’t total elimination, but staying ahead of their life cycle.

Why March Is Fly Prevention Month

If you wait until you see flies, you’re already behind. Smart March cattle management starts with fly control before populations explode. It’s about getting ahead of the fly life cycle.

• Flies overwinter in manure and hay waste.
  Horn and stable fly pupae survive in old manure piles, under hay rings, and around feeding areas. As temperatures rise, they emerge fast.
• Stable flies develop where you feed hay all winter.
  That leftover hay mixed with moisture and manure? Perfect breeding ground. If you fed hay in the same spots all winter, expect early stable fly pressure there first.
• IGRs must start 30 days before fly emergence.
  Insect Growth Regulators (IGRs) do not kill adult flies; instead, they stop larvae from developing. This means you need to use them before flies hatch. This timing is important for proper horn fly prevention.
• Tag timing matters.
  One of the biggest mistakes producers make is putting fly tags in too early. If you apply them before fly numbers reach threshold levels (around 200 horn flies per cow), you increase the risk of resistance and shorten tag effectiveness. Knowing when to put fly tags on cattle protects both performance and product longevity.
• Spring is when resistance mistakes happen.
  Using the same chemical every year, leaving tags in too long, or treating too early all contribute to the development of resistant fly populations.

Know Your Enemy: The 3 Flies Costing You Money

Horn Flies: The Billion-Dollar Pest

• These are typically smaller than the other types you will deal with, usually 3/16″ in length. They are blood feeders that require more than 30 meals per day.
  

  Courtesy of University of Florida Entomology

• They are typically found on cattle’s backs, sides, and poll areas. They can also be seen on cattle’s belly regions during warm summer afternoons.
• Though they are small in size, their impact on the cattle industry is enormous. Economic losses from them are estimated at more than $1 billion annually.
• Since they feast on blood, they can also cause weight loss in cattle. Studies in the U.S. and Canada have shown that horn flies can negatively impact weaning weights by 4-15%.
• Typically, these flies travel only a short distance, so controlling them will be easier.
• Management: Multiple insecticide options are available to manage horn flies, such as dust bags, feed additives, pour-ons, and medicated ear tags

Face Flies & Pinkeye: The Hidden Cost

• When these are adults, they can look very similar to house flies, though they are slightly larger and darker. Another thing that separates these from the other types is that, as the name implies, they will be found chiefly on the face area of a cow.
• It is a non-biting fly that feeds on animal secretions, nectar, and dung liquids. The adult female will cluster around the cow’s eyes, mouth, and muzzle. As you might guess, this can be quite irritating
  

  Courtesy of University of Nebraska-Lincoln Entomology

  to your cattle.

• They can be found throughout the summer months, but their population numbers usually peak in late July and August. Also, they will be more numerous along waterways and areas with abundant rainfall.
• These flies have been shown to travel farther distances than most, usually 1-2 miles. So, if your neighbors are not taking steps to control these, it will be nearly impossible for you to do so.
• While feeding, they can cause damage to the eye tissue, increasing the chance of an infection in the eye. One of the most common infections is pinkeye, a contagious inflammation of the cornea. I discussed the steps you can take to prevent and treat pinkeye in a previous article, “Ultimate revelation of cattle pink eye.”
• Management: They can be challenging to manage because they only spend some of their time on cattle. Effective control may require different methods, such as ear tags, dust bags, and sprays. To be most effective, we will need to treat both cows and calves.

Stable Flies: The Weight-Gain Killers

• As with horn flies, this is a blood feeder that poses a severe problem in feedlots, dairies, and pasture cattle. A producer will mainly find them on the animal’s front legs.
• The bites from these insects are painful and will cause cattle to stomp their feet or bunch together in the corner of a pasture to get away from them. To avoid these little pests, they make cattle
  

  Courtesy of University of Florida Entomology

  stand in water.

• Typically, these flies will develop around feed bunks, under fences, and around hay stacks. Also, sites where you feed hay during the winter with hay rings can be a source of larvae development if the right amount of moisture is present.
• Cattle will lose weight and produce less when stable flies are overabundant, just like the Horn fly. Studies have shown a reduction in average daily gain, or ADG, of about 1/2 lb per head.
• Management: Using insecticides may be difficult to get control because they tend to swarm around the animal’s legs. Spraying will likely be your best option, but it will require weekly applications to manage populations.

Smart Fly Control: What Actually Works

Feed an insect growth regulator.

• • Usually, you can get this with certain types of mineral supplements, such as Altosid or Rabon.
  • Altosid is labeled just for Horn flies, and Rabon is labeled for Horn, Face, and Stable flies.
  • To be most effective, you must start putting this out 30 days before flies typically begin to emerge and continue feeding it until 30 days after a killing frost.
  • This product stops the growth cycle during the larval stage.

Fly Tags

• • Some of the fly tags now being released have a higher insecticide concentration. They are very helpful in controlling fly populations.
  • There are two types to choose from: pyrethroids and organophosphates. What you want to do is use pyrethroid tags for 2 years, then use an organophosphate for 1 year to reduce resistance.
  • Depending on the type you use, it may require 2 tags per adult and 1 tag per calf for optimal control.
  • The key is to wait until you have 200 flies per cow before using them. Using them too early can reduce their effectiveness.
  • Remove the tags after 3-5 months of use to prevent the possibility of resistance.

Pour-Ons

• • You will want to apply this at the same time you put the tags on your cattle.
  • When doing this in the spring, you can use a product that also kills internal parasites, as these products have proven effective at preventing horn flies. Use a fly and/or lice control product if it is later in the year. This product will stop the likelihood of internal parasite resistance.

Dustbags/cattle rubs

• • It can effectively control Face and Horn flies if placed at a site where all cattle will use it.
  • Keeping them charged with insecticide and putting them in the proper places is the key to using this.

Sprays

• • Spraying your cattle throughout the year can effectively control the fly populations on your ranch.
  • However, this product can be very time-consuming if your cattle are grazing over a large area.

Avoid Creating “Super Flies”

• Using fly tags too early.
  If you put tags in before fly numbers reach the economic threshold (around 200 horn flies per cow), you expose a small fly population to insecticide for a long period of time. The strongest flies survive — and pass that resistance on.
• Leaving fly tags in too long.
  Tags should generally be removed after 3–5 months. Leaving them in after the insecticide level drops exposes flies to low doses, which is one of the fastest ways to build resistance.
• Using the same chemical class every year.
  Rotating between pyrethroid and organophosphate tags helps slow the development of resistance. If you use the same active ingredient year after year, horn flies especially will adapt.