Sometimes called Cleg Flies, adult Horse Flies feed on nectar and sometimes pollen. Females usually also feed on blood which aids in egg development. Males lack the necessary mouth parts for blood feeding. Most Horse Flies feed on mammal blood, but some species are known to feed on birds, amphibians or reptiles.
The females’ primary sense for locating prey is sight, and they have large compound eyes that serve this purpose well. The flies usually lay waiting in shady areas for prey to happen by. They are attracted to large, dark objects, and to certain animal odours and carbon dioxide. They are also attracted by motion, their eyes being well adapted to its detection.
The eyes of Horse Flies are generally brightly colored, and this colouration is one of the means entomologists use to identify them to species, though the colours rarely persist after death.
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LNHG Biological Records Manager