We seldom talk about black flies but I have recently run across problematic black fly strikes in northern Alberta.
Black flies are very small and can elicit painful bites that can cause swelling in people, dogs, horses and cattle.
Deaths can result from black fly strikes in animals that have not experienced them before and are introduced to a black fly area. This is usually breeding bulls but the rest of the cattle will suffer production losses from the bites.
Black flies have their life cycle completed in running water. Periods of more spring runoff and rainfall can lead to an increase in black fly populations.
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Bites often are seen around the face, ears, neck and abdomen of cattle and I have seen severe biting evident on scrotums of breeding bulls as well.
The irritation caused by the flies can limit grazing, which can significantly affect weight gains. Black flies don’t like dark or closed-in areas so cattle can get relief by seeking cover, including in sheds with three walls and open front.
The only way for decent prevention is the continual use of an insecticide during the periods of intense activity. This is really accomplished by cattle oilers or dusters.
Oilers can be charged with the insecticide during periods of high fly numbers. The permethrins are the insecticide group commonly used. Other effective products such as Malathion are no longer available in Canada as an insecticide.
Black flies are small and are also called buffalo gnats because of the distinct hump in their back that resembles the hump on a bison. They are small and fast and are also commonly known as no-see-ums.
In some areas, especially around flowing water, they can be a big problem. In my experience in Alberta, the farther north you go, the worse they seem to get.
Animals that have never been previously exposed to areas with large numbers of black flies can be vulnerable to a toxin released in the flies’ bites and depending on the number of bites, previously unexposed cattle can die.
I have run into several incidents of this in breeding bulls being introduced to the herd from out of the area. The fly bites can cause weakness, lethargy and death.
The bites are clearly visible but usually by the time you see clinical signs, it is too late to treat.
In these cases, treatment would be the insecticides for stopping the fly bites and medications for shock and inflammation.
You can see thousands of fly bites when treating.
The female flies do the biting to get a blood meal before laying eggs.
In a black fly onslaught, treatment is imperative. It is best to introduce new animals from outside the region before the peak black fly season begins.
Sometimes black fly problems occur earlier in the spring than the typical horn and face fly issues, which usually occur in mid-summer, often peaking in July.
Black fly issues generally start much earlier and producers must be on heightened awareness in the high population areas. With fly control (horn and face flies) in general we want to treat when the fly numbers get high to avoid overtreating or treating continually, which leads to development of resistance.
Make sure that black flies are listed on the insecticide label when you use them or get a recommendation from your veterinarian or other agricultural consultant.
Make sure label directions are followed.
If you are pasturing animals in a different region, away from home, or are using a new pasture, know the local issues.
Producers should track peak fly periods, as well as other factors such as incidence of redwater disease, the presence of poisonous plants such as larkspur or water hemlock, if any anthrax has been reported in the area in the last few years and any water quality issues.
Ask the neighbouring cattle producers so you know what you’re getting into.
Have a great grazing season and always try and maximize gains and health at pasture with monitoring and by using the tools and advice we have at our disposal.
