Insects, also referred to as "mosquito hawks," that are about 1-inch long with wings and long legs. In larvae form these flies resemble brown worms known as "leatherjackets." Most adult crane flies are harmless. Leatherjackets, however, feed on grass roots, causing the most damage to growing grass in spring. Thatch often provides hiding places and food for these larvae. Proper lawn treatments, such as core aeration, can prevent infestations.