Lesions consist of self-inflicted hair loss and excoriations with crusting. Larvae develop in aquatic habitats and decaying vegetation and manure. These Insects feed on horses in great numbers and can produce significant blood losses and annoyance. Skin eruptions can appear on horses bitten by mosquitoes. Mosquitoes reproduce in large numbers in standing water found in marshes, irrigated pastures, abandoned tires and old feed pans.
Many species can fly several miles from their breeding sites to feed.
Three species of bots are considered serious pests of U.S. horses. The bot is the larval stage of the horse bot fly, Gastrophilus species. Bot fly species vary in where they lay their eggs on the horse and how the eggs hatch. In general, they lay eggs on the forelegs, shoulders and lips during the summer and fall. The eggs hatch when the horse licks and rubs them.