Diptera (Flies)
The order Diptera include the flies, which can be differentiated from other insects by their one pair of flying wings, and modified hind wings called "halteres." Diptera are holometabolous, meaning they spend their immature stage as a larva, pupate, and then emerge as adults.
Resources
Photo by M.E.S. Member Roger Rittmaster: Eastern Hornet (Fly Spilomyia longicornis)
M.E.S. Member Photos of Diptera
Chionea valga (Diptera: Limoniidae) 5 January 2014; Ross Rd. Blueberry Plains, Old Orchard Beach (York Co.) By Brandon Woo