Frequently Asked Questions

ClariFly® Larvicide is an EPA-registered feed additive with an active ingredient that controls house, stable, face, and horn flies in areas populated by confined beef and dairy cattle, swine, and equine.
Insects have an external skeleton, an “exoskeleton” made of chitin. The active ingredient in ClariFly® Larvicide targets immature flies by either contact or ingestion, and inhibits the deposition of chitin during motling. Without a functioning exoskeleton, the larvae die before they can become breeding adult flies that can bother your animals.
Start feeding ClariFly® Larvicide early in the spring, 30 days before flies begin to appear, and continue feeding throughout the summer and into the fall, until cold weather restricts fly activity. To minimize the number of over-wintering pupae, feed ClariFly® Larvicide 30 days past first frost. 
ClariFly® Larvicide does not harm parasitic wasps. Wasps that parasitize fly pupae seek out pupae in the field. The female wasp drills a hole into the pupa and lays eggs inside the pupal case of the fly. As the immature wasps develop, they feed on the fly pupae that is transforming into an adult, killing the fly in the process. Fly larvae in ClariFly® Larvicide treated manure die before they can form pupae, so the wasps are unaffected. ClariFly® Larvicide can have a negative impact on dung beetle larvae (but not adults) that feed on manure from treated cattle.

The active ingredient is a pesticide that poses a low risk to human health and the environment. It has the following advantages over existing conventional pesticides:

  • Low impact on human health
  • Low toxicity to non-target organisms (birds, fish, plants)
  • Low potential for groundwater contamination
  • Low use rates
  • Compatibility with integrated pest management (IPM) practices
ClariFly® Larvicide is approved for beef and dairy cattle, swine, and horses.
ClariFly® Larvicide is an EPA-registered product because the activity takes place outside of the animal. Products whose activity takes place inside the animal, such as dewormers for the control of internal parasites, are regulated by the FDA.
Yes, the active ingredient has been pelleted in animal feeds at temperatures up to 200 degrees Fahrenheit without noticeable process losses.
The half-life of the active ingredient in soil is less than seven days.
No, ClariFly® Larvicide won't harm employees when handled according to label directions. As part of the approval process for ClariFly® Larvicide, the U.S. EPA evaluated the occupational exposure from the normal use of the product and concluded it was harmless.
The metabolism of the active ingredient in cattle has been extensively studied in dairy cattle. The EPA has established tolerances for milk, animal fat, meat and meat by-products at 0.05 ppm. Metabolism studies in dairy cows showed no detectable levels of the active ingredient residues in milk when dosed for up to 28 days. In studies of dairy cows, only very low levels of the active ingredient were occasionally seen in liver, kidney, fat and muscle. Therefore, there are no withdrawal requirements when using ClariFly® Larvicide.
ClariFly® Larvicide should not impact the performance of products used to reduce phosphorus levels in pig manure. In addition, the active ingredient and carrier will not increase the amount of phosphorus being deposited in the manure.
When formulating for a group of animals that range in weight, it is recommended to formulate for the heaviest animals in the group to ensure that all animals receive an effective dose. Lighter weight animals may receive a higher dose per kg of body weight for a time, but only if they are consuming the same amount as the larger animals. Many times this is corrected for, as the lighter weight animals are consuming less feed. It is important to treat ALL manure output to have maximum effect to control flies.
In a study, pigs were dosed for 10 consecutive days and followed for 14 days after the last dose. The study showed that the majority of the active ingredient, approximately 80%, was passed through and found in the feces as unchanged. Approximately 10% of the administered dose was excreted in the urine. The urine contained metabolites and only a small amount of the active ingredient. Small amounts of the active ingredient were stored in tissues, mostly in the liver and kidney. However, 14 days after the last dose, no detectable levels of the active ingredient or its metabolites were still found in pig tissues.
Breeding studies have not been done specifically in pigs with ClariFly® Larvicide, but the active ingredient has been extensively studied in laboratory animals. A study in rats showed no adverse effects on the ability to breed and produce healthy offspring over two generations while continuously consuming the active ingredient in the diet at doses up to 500X higher than the label dose of the active ingredient for pigs. Studies in rats and rabbits show that the active ingredient does not cause birth defects.
Studies show that most of the active ingredient passes through unchanged. A small fraction is absorbed, metabolized and excreted in the urine.
Breeding studies have not been done specifically in horses with ClariFly® Larvicide, but the active ingredient has been extensively studied in laboratory animals. A study in rats showed no adverse effects on the ability to breed and produce healthy offspring over two generations while continuously consuming the active ingredient in the diet at doses up to 1,000X higher than the label dose of the active ingredient for horses. Studies in rats and rabbits show that the active ingredient does not cause birth defects.

To control manure-breeding flies, all cattle on the premises need to consume adequate quantities of ClariFly® Larvicide every day. The feeding level for this product for cattle over 200 pounds is 0.10 mg of the active ingredient per kg of body weight per day.

Daily consumption of ClariFly® Larvicide by individual animals may vary. However, fly control will not be affected.


Because the inclusion rate of ClariFly® Larvicide is dependent on the weight of the animal, the cost per head per day will vary as the animal increases in size. As a general rule, it will cost 4/10 – 5/10 of a cent per hundred pounds of body weight per day. For example, it should cost between 2 and 2.5 cents per day to treat a 500 pound calf.
The metabolism of the active ingredient in cattle has been extensively studied in beef cattle. The EPA has established tolerances for milk, animal fat, meat and meat by-products at 0.05 ppm. In studies of beef cattle, only very low levels of the active ingredient (below the meat tolerance) were occasionally seen in liver, kidney, fat and muscle. Therefore, there are no withdrawal requirements when using ClariFly® Larvicide.
Horn flies take up to 40 blood meals on cattle per day, congregating on their backs and sides. These annoying, painful bites can cause cattle to go off feed, reducing weight gain and milk production. It is estimated the horn fly costs the North American cattle industry $1 billion per year.
Beef mastitis is one of the diseases spread by horn flies. Taking up to 40 blood meals a day, horn flies can cause cattle constant discomfort if left unprotected. Horn flies tend to feed on the blood vessels in the skin of the teat, causing irritation.