Is a motorcycle license needed?

For dirt bikes and ATV's, a motorcycle license IS required. If you straddle the seat and the vehicle has handlebars, you will need a motorcycle license, even if the vehicle has 3 or 4 wheels. 

Unless you are in NY, or MA, if your vehicle is 3 or 4 wheeled, such as a UTV or Polaris Slingshot, then no motorcycle license is needed. You will simply need a standard driver's license. You can read about this HERE.