T. equalis . Tabanus atratus is one of the most easily recognized and notorious horse flies in eastern North America. This large, bluish-black fly with black wings can exceed 1 inch in length and inflict a very painful bite. Most Missouri horse flies have aquatic larval stages. The mother flies affix their eggs to vegetation near ponds and streams and the hatching larvae drop into the mud or water, where they live as predators for up to several years, depending on the species.
Horse flies seem to be present all summer long.
In fact, synchronous emergences result in one species being present for a time, then being replaced by another species, and so on. To cattle, however, it means being bitten the entire summer. Female horse flies seek blood as raw material for energy and to manufacture eggs. The flies are evidently sensitive to parts of the electromagnetic spectrum that humans cannot see. Humans are often bitten, especially around swimming pools, streams and ponds and on walks in the woods.