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Bug Report: Deer Flies

Deer FliesDeer flies belong to the same family as horse flies and therefore the two have many similar characteristics.

The good news about deer flies and horse flies is that they're more interested in biting animals than biting people. The bad news is that these flies can significantly impact some animals.

In Canada, deer 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. They prefer to feed on animals such as caribou, moose and cattle.

In some cases, cattle can spend so much time fending off deer flies that meat and milk production are curtailed. The deer 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.

While horse fly larvae are capable of inflicting a painful bite if handled, scientists do not know whether deer fly larvae share this characteristic. Both are equipped with a similar set of mandibles but it's not known how deer fly larvae use theirs.

You can spot deer flies by their boldly patterned wings and you may see them 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 deer 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 James Castner, University of Florida

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