Horse flies are attracted to such things as movement, shiny surfaces, carbon dioxide, and warmth. Once on a host, female horse flies use their knife-like mouthparts to slice the skin and feed on the blood pool that is created. Bites can be very painful and there may be an allergic reaction to the salivary secretions released by the insects as they feed. In rare instances, there may be allergic reactions involving hives and wheezing. Their painful bites generally elicit a response from the victim so the fly is forced to move to another host. Consequently, they may be mechanical vectors of some diseases. Male horse flies feed on nectar and are of no consequence as a pests. Females lay batches of 25 to 1,000 eggs on vegetation that stand over water or wet sites. The larvae of horse fly species develop in the mud along pond edges or stream banks, wetlands, or seepage areas. The larvae stage usually lasts from one to three years, depending on the species. Mature larvae crawl to drier areas to pupate and ultimately emerge as adults.