Few insects are hated as much as the horse-fly. There are various species: the photo above is a deer-fly. The common horse-fly (photo below) is slimmer, gray with greenish eyes. Female horse-flies are blood-thirsty and suck blood from large mammals including people. The protein in the blood is necessary for the eggs to ripe. To get to the blood, the flies have a small sharp knife attached to their mouth. The male horse flies eat nectar. The larvae live in damp soil. Some consume meat; others live off of rotting plants. In moist dunes and salt marshes, such as the Boschplaat on Terschelling, horse-flies can be found in massive amounts, particularly during warm humid summer days.