Bug Report: Horse Flies

Horse flies belong to the same family as deer flies and therefore the two have many similar characteristics.

In Canada, horse flies are most numerous in areas containing ponds, marshes, streams or bogs, and come out only during the day from June to August when the weather is warm.

Like deer flies, horse flies are more interested in biting animals than biting people. However, horse fly larvae are capable of inflicting a painful bite if handled. But chances are you won't be handling horse fly larvae in your everyday life.

Horse flies prefer to feed on animals such as caribou, moose and cattle. In some cases, cattle can spend so much time fending off horse flies that meat and milk production are curtailed.

The horse fly's tendency to feed, get distracted and leave, then return for more feeding, also means that cattle, caribou and moose can end up with numerous bites from the same fly.

Horse flies differ in appearance from deer flies by their wings. The wings of horse flies are transparent, while the wings of deer flies are boldly patterned.

Speaking of wings, you may encounter horse flies hovering on hilltops, in sunlit clearings, or along forest paths. Adult males are equipped with large amounts of nectar, which provides them with enough energy to hover in one spot for minutes at a time. Adult females meantime prefer less hovering and more feeding.

Laboratory experiments have shown that horse flies are capable of transmitting some diseases to animals. And although extremely unlikely, these diseases can be transmitted to people who have been in contact with infected animals. However, there have been no cases of this occurring in Canada.

Some information courtesy of Agriculture and Agri-Food Canada
Image courtesy of Bruce Marlin, photographer