Adult horse and deer flies are active primarily during warm weather in spring and summer in the north, year-round in Florida and other southern environs. Most species prefer open, grassy habitats near fresh water, where their eggs are deposited on vegetation and the larvae either drop into the water or burrow into mud along the banks [1].

Both male and female adult tabanids feed on flower nectar. As with most insects requiring a blood meal for reproduction, females are the ones responsible for provisioning; they do so by biting mammals, some large, including humans, cattle, deer - and of course, horses. Some species prey on birds, reptiles, or amphibians [2]. Male tabanids are rarely seen and do not bite.

Larvae eat plant material, or are predacious on small invertebrates. Some species spend several years in the larval state. It has been suggested larvae of Tabanidae species deposited in water may be an early indicator of water quality, as are the nymphs of dragonflies and damselfies (odonata), and other sensitive organisms that depend on contaminant free, oxygenated water for their development.  Lots of horse flies is good news for our watershed!