Diptera, or commonly known as the flies family, is a diverse order of insects that contains hundreds of thousands species.
The variety members of this order are spread around the globe.
Many of the species in this insect order spread diseases.
Common pest of this order are Mosquitoes and House Flies.
Each of them were evolved to live in different lifestyles - different habitat and different foods.
Here is a Family Tree for the Diptera Superorder.