Face fly nightmare

Face flies beginning to appear a few days after my initial treatment with AiM-L VetCaps.  I unfortunately don't have any photos of the original mob of flies, which was much worse.

Since the forth of July an insect called the face fly (Musca autumnalis) has plagued our ranch and caused me a considerable amount of stress.  It was a week ago, on the forth, while doing a routine check on the herd, that I noticed that the bison appeared to be greatly agitated by a surprisingly high number of the flies.  While the sight of flies or other small insects buzzing around grazing animals is nothing unusual, this was something different.  The flies flocked in groups around the eyes and nose of each animal so incessantly that the bisons' natural defenses appeared to be ineffective.  All the blinking, ear flapping, tail wagging, snorting, rolling in soil, and rubbing on trees had little effect.  No matter how many times they did these things the flies would just briefly fly up into the air and then immediately settle back down.  This scene left me unsettled and I immediately started researching it's causes and working on a solution.  The following describes these efforts.  

A bison blinking in a vain attempt to discourage face flies.

Before I describe my attempts to combat this fly, it will be useful to first provide a brief description of what I have learned about the fly itself.  Prior to the 1950s (some say the 1940s), the species Musca autumnalis, commonly called the face fly, did not exist in North America.  Up until that point they were only found in Europe, Asia, and Africa.  As is often the case when lifeforms are introduced into a new environment with no natural predators, face flies rapidly expanded their territory in the United States from three eastern states in 1958 to states as far west as Nebraska by 1960.  They now cover most of temperate North America.  

The face fly life-cycle is fairly straight forward.  Eggs are deposited on fresh manure where they develop, hatch, and pass through larva and puparium stages before maturing into adults.  

It is at its mature stage that the face fly causes problems.  Unlike other problematic flies, such as horse and deer flies which feed on blood they painfully extract with a piercing proboscis, face flies feed on tears and mucous with its mouth.  While this method of feeding may seem relatively harmless when compared to the biting flies, it can actually do quite a bit of damage.  The face fly mouth, though less intimidating, contains small stomatal teeth which are used in a rasping manor when feeding.  This method of feeding benefits the fly in two ways: first, it removes small amounts of skin tissue which is eaten along with the tears and mucus, and, second, it induces the production of more tears and mucus.  The damage produced by this form of feeding, when multiplied by a large number of flies, produces a great deal of pain and irritation in cattle and bison.  Additionally, these flies can transmit pink eye (which can cause blindness) and even eye worms to their hosts.  I have found more than one article out there that describes face flies as having a minimal impact on livestock productivity and more of an "aesthetic problem" to producers than a problem to cattle, but I would think that most cattle would consider potential blindness a problem. 

Although the large majority of information available on face flies appears to focus on cattle, there is some information concerning bison.  Given the lack of reference citations in the information I've found on the Internet (not that I'm blaming anyone, cause I don't do it either), it's hard to establish what is true and what isn't.  However, based on what I could find, it appears that, for bison, the primary concern from a herd health perspective is the potential for pink eye to take hold and spread through the herd.  Pink eye or infectious keratoconjunctivitis, if left unchecked, can sometimes leads to blindness and, while not as dire as the outcomes of such agents as Yersinia pestis or Bacillus anthracis, it would really suck to have a herd of blind or partially-blind bison.  

Upon the conclusion of my research into face flies and their potential impact, I next began my quest to find a way to reduce the massive swarm of face flies before pink eye could be introduced.

Based upon my limited research it appears that there are a number of methods available that are considered "organic," which I would consider preferable.  Unfortunately most of these methods appear to focus on preventing the fly population from becoming large rather than reducing a large fly population.  On one website I read that there are certain synthetic chemical pesticides that are technically considered "organic," which is somewhat difficult for me to comprehend.  Perhaps in the future, when time is on my side, I will find a method to control face flies that is considered "organic," but, for the short term I will need to stick to my own moral compass rather than a regulatory one.

By far the most frequently used method for stopping face flies from inundating bison and cattle is to apply small amounts of relatively short-lived insecticides to the animals.  A variety of chemicals are approved for such use, but, for me, the main challenge was finding a way to actually apply the chemical to each bison without either getting myself killed or causing the bison undo stress.  The following is a description of the methods I have tried thus far and a complication that emerged during the process.

The VetGun.  This method uses what is essentially a modified paintball gun to shoot a small ball containing the insecticide at the animal under a reduced pressure.  Upon impact with the animal's shoulder the ball bursts dispensing the insecticide.  The effective range of the gun is 15 to 30 feet.

The first application method I attempted was a specialized paintball gun called a VetGun.  While not cheap, the VetGun appeared to be an ideal way to apply an insecticide to bison and I placed an Internet order with upgraded overnight shipping.  Though trivialized in some literature, I had a bad feeling about the face flies, and wanted to get started on treatment as soon as I could.  A day and a half later the VetGun arrived and I immediately headed for the ranch.  Unfortunately, my premonition turned out to be true and pink eye had started. 

Pink eye or keratoconjunctivitis in the left eye of bison number eight somewhat reduced in severity since the start of treatment with antibiotics.

About halfway through the insecticide application, which I managed by slowly driving the tractor in circles near the hear while periodically shooting one with a ball,  I noticed that the left eye of No. 8 had turned completely white from the infection.  Based on the way she walked it was apparent that she was blind in that eye.  Disheartened, I continued apply the insecticide while simultaneously examining the others.  In all I would say that at least half of the herd showed signs of pink eye infection in at least one eye with No. 8 being the worst case.  

The insecticidal balls come in pack of 30 and cost around $78 a pack. The dosage should be one ball per animal and is supposed to be effective for around four weeks. 

As soon as I completed the application process, I called my veterinarian.  The vet was able to confirm the diagnosis and gave me steps for treatment.  The first step, stopping the flies, was already in progress, and the second step was to help the bison get over the infection.  While many animals might benefit from such common treatments as topical eye ointments and glued-on temporary eye patches, the vet agreed that such methods would be impractical with bison and the best method would be to feed them for a period of time with a specified amount of feed treated with chlortetracycline antibiotic.  This would be the best way to stop the spread of the infection in the herd.

A closeup of one of the balls.

With this advice from the vet, I began the treatment with antibiotics that same day and, over the next few days, monitor the situation.  Initially, everything seemed to be going fine.  The overwhelming cloud of face flies dissipated and the signs of pink eye start to fade.  However, on the forth day after the VetGun treatment, the flies returned and I renewed my search for a more effective application method.  Here are two that failed:

My attempted application of insecticide with a dust bag.  This device, commonly used for cattle, aroused extreme suspicion in the bison.  In fact, the sight of the hanging bag appeared to alarm the herd so much that I thought bull might charge it and destroy the stand.  Even the addition of a much coveting salt block could not overcome the bisons' mistrust of the mysterious hanging bag.  

Super sneaky night-time application mission:  After being bombarded by balls from the VetGun, the bison were finished allowing me to get close, so I decided to attempt to sneak up on them at night while wearing a backpack sprayer and covertly apply spray to each animal while they slept at night.  I had everything planned in great detail included how many seconds I needed to spray the back of each bison to get the proper dose.  This is by far the stupidest and most dangerous idea I've had in a long time.  Thankfully it never proceed far enough to even become dangerous.  I had gotten to within 150 yards of the herd (which I could clearly see resting in the pasture through my NVGs) and was considering the best way to crawl under the electric fence without making noise, when I noticed that they had detected me and were taking countermeasures.  Unsure of exactly where or what I was they stood, formed into a row, and, began to silently march towards me.  With the tables now turned I retreated in defeat.

After several failures and my pathetic attempt at sneakiness the previous night, I finally came up with an idea that works.  Seeing as I have to feed them their medicated feed anyway I thought of a way to have them apply the insecticide to themselves while they ate.  This method, based loosely on the "four poster system" used to reduce tick infestations on wild white-tailed dear, is simply a long metal rod threaded with 12 paint roller covers and placed lengthwise down the center of a feeding trough.  The metal rod, which came from one of my 10 foot t-posts with the anchor plate popped off with a hammer, was attached to the trough with wire at each end.  Finally, prior to filling the trough with feed, I treated the roller covers to 15mL each of a 2% permethrin solution.  The original "four poster" experiment I read about used a 10% solution, but that seems a little high, so I'll start with 2% and see if that works.

Two troughs ready for the bison.  Only a small amount of the feed you see in this photo is actually medicated.  The vet told me they probably wouldn't like the taste of the medicated feed, so I should try to mix it with some sweet feed.  They really like the sweet feed.

The bull's personal bowl:  During the first day of treatment I only had one trough, but the short comings of a single trough became quickly apparent.  Our dominant bull so enjoyed the sweet feed that he decided it best to bogart it as much as he could.  For that entire feeding he stood at one end of the trough and drove away any who attempted to approach that end.  Even after he was full he remained at the trough guarding the feed.  The result was that there was only enough room for two or three others to eat an any one time.  The next night I used two troughs with the same amount of feed, but, though better, the results weren't ideal.  Though more bison were able to eat at any one time, our hero was still quite disruptive and tried to eat more than his share.  Finally, at this last feeding I added a large bowl brimming with about 10 pounds of pure sweet feed and set about 10 feet away from the troughs.  The bowl proved irresistible and kept him busy for the first 30 minutes allowing the others to eat in peace.

In addition the to successful use of the bowl, the permethrin applicators worked well.  The insecticide was placed precisely where I wanted it and nowhere else. 

Even the slightly smaller bull calves got the treatment.