There are an estimated 1,100 different species of bats worldwide, accounting for 1/5 of the world's mammals. Forty-seven bat species are currently found in the United States.  The largest bat living in the United States is the western mastiff bat (Eumops perotis), which weighs approximately 2 ounces and has a wing span of nearly 2 feet.

Bats are grouped into two suborders, Megachiroptera (megabats) and Microchiroptera (microbats/echolocating bats). Microbats differ in that they lack the claw at the second toe of the forelimb, eat insects, blood, small mammals, and fish, and use echolocation for navigation and finding prey. Echolocation is the emittance of high pitched sounds that bounce off of objects and produce echoes, allowing the bats to judge the distance and size of objects in their path. Megabats, which are generally larger in size, eat fruit, nectar, or pollen. 

Long tongues assist megabats that feed on nectar, while special "nose leaves" (flaps and folds of skin) assist microbats that echolocate with their nose.  Bats that echolocate also often have huge ears compared to the rest of the body.