Difference Between Two Suborders of Bats

All bats fall under the order Chiroptera into one of two suborders: Megachiroptera and Microchiroptera (or megabats and microbats).  The names do not refer to size.  All bats of both suborders can be any range of sizes anywhere from the size of a small dog with a 2 meter wingspan wieghing 1.5 kilograms to the size of a bee weighing 2 grams.  All megabats reside in the "old world" (before columbus) in tropics and subtropics while microbats can be found all around the world.

Megabats feed almost exclusively on flowers and fruit.  They have large eyes and typically dog-like faces.  Megabats rely on smell and vision to find food and do not use echolocation with the exception of the Egyptian fruit bat, which does incorporate a form of echolocation.

Microbats have more varied tastes including: insects, fruit, pollen, nectar, fish, frogs, blood, and even other bats.  They have small eyes and often elaborate facial construction.  All microbats use echolocation to detect their prey.
http://www.bats.org.uk/pages/bats_of_the_world.html