All tabanids overwinter in the soil as larvae. Most favor wet mud, near or under ponds, marshes or streams, or in sphagnum moss in bogs, although a small number of species live in drier habitats. A few rare species occur as larvae only in gravel under swiftly flowing water. Some species, especially in the last two categories, are choosy as to their habitat, but the larvae of perhaps the majority of species have been collected in a variety of wet muddy habitats near various water bodies. With present knowledge it is not as easy to predict what species might occur in a given habitat as it would be for mosquito or black fly larvae.
Tabanid larvae are also fairly mobile, and as they live for many months.
Horse fly larvae are fierce predators, capturing their prey, usually the larvae of other insects, with their sharp sickle-shaped mandibles and paralyzing them with an injection of venom like a rattlesnake. A particularly large species in the southern USA can capture newly hatched toads and drag them under the mud. An injection of the venom immobilizes the prey almost instantly and probably also aids in liquefying its tissues which are then sucked out leaving an empty skin. Horse fly larvae are capable of inflicting a painful bite if handled. Deer fly larvae are equipped with a similar set of mandibles with venom glands but no one is sure what their food consists of or how their mandibles are used.