Moose Flies and Moose

My recent quest for finding moose was successful – and my most striking observation, other than their imposing size, was the presence of a multitude of flies on and around the hindquarters of every moose I saw. I assumed they were deer flies, but they didn’t appear to be bothering the moose and research revealed that, in fact, they were moose flies, Haematobosca alcis. These flies can be seen throughout the spring and summer in dense swarms over and on the rumps of moose — five hundred or more may accompany a single moose. Unlike most other biting insects, both male and female moose flies feed on their host’s blood. Although not considered a serious pest (moose tend to pay little attention to them), moose flies may be responsible for sores often found on the hind legs of moose. It is thought that female moose flies may be stimulated by gases released by the moose when it is defecating, after which the female flies descend and deposit eggs into crevices in the moose’s scat.

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