The Tabanidæ,—horse-flies, ear-flies, and deer-flies,—are well-known pests of cattle and horses and are often extremely annoying to man. The characteristics of the family and of the principal North American genera are given in the keys of Chapter XII. There are over 2500 recorded species. As in the mosquitoes, the females alone are blood suckers. The males are flower feeders or live on plant juices. This is apparently true also of the females of some of the genera.
The eggs are deposited in masses on water plants or grasses and sedges growing in marshy or wet ground. Those of a common species of Tabanus are illustrated in [figure 80, a]. They are placed in masses of several hundred, light colored when first deposited but turning black. In a week or so the cylindrical larvæ, tapering at both ends ([fig. 80, b]), escape to the water, or damp earth, and lead an active, carnivorous life, feeding mainly on insect larvæ, and worms. In the forms which have been best studied the larval life is a long one, lasting for months or even for more than a year. Until recently, little was known concerning the life-histories of this group, but the studies of Hart (1895), and Hine (1903 +) have added greatly to the knowledge concerning North American forms.
Many of the species attack man with avidity and are able to inflict painful bites, which may smart for hours. In some instances the wound is so considerable that blood will continue to flow after the fly has left. We have seen several cases of secondary infection following such bites.
The horse-flies have been definitely convicted of transferring the trypanosome of surra from diseased to healthy animals and there is good evidence that they transfer anthrax. The possibility of their being important agents in the conveyal of human diseases should not be overlooked. Indeed, Leiper has recently determined that a species of Chrysops transfers the blood parasite Filaria diurna.
Leptidæ or Snipe-Flies
The family Leptidæ is made up of moderate or large sized flies, predaceous in habit. They are sufficiently characterized in the keys of Chapter XII. Four blood-sucking species belonging to three genera have been reported. Of these Symphoromyia pachyceras is a western species. Dr. J. C. Bradley, from personal experience, reports it as a vicious biter.
Oestridæ or Bot-flies
To the family Oestridæ belong the bot and warble-flies so frequently injurious to animals. The adults are large, or of medium size, heavy bodied, rather hairy, and usually resemble bees in appearance.