Microbats (suborder Microchiroptera)

*see also "Differences Between Suborders of Bats" for very basic information

Microbats are insectivorous, mostly eating insects with the major exception of the ghost bat from Australia, which has been known to eat frogs, birds, lizards and mammals even including small bats.  They range from 3-150 grams and typically have wingspans around 25cm.  They are nocturnal and use echolocation and poor eyesight to locate prey.  Only 2 species of bats have potentially audible echolocation frequencies, but most sounds we can hear bats make are either social chatter, communition with young, and alarm calls.  Microbats have been recorded to find prey as efficiently as one insect every three seconds with their excellent echolocation.

Microbats fly at a range of speeds with varying maneuverability, from slow, fluttery, and controlled to fast and much less easily controlled.  Microbats typically catch and eat their prey while in the air, but they can also "glean" insects that are not in the air and pluck them off surfaces or out of webs.  They do this either by flying slowly and identifying the insect on the plant with echolocation or by perching nearby and simply listening to the movement of the insects.

Microbats like to roost in caves, tree hollows, and many other small crevices including manmade crevices typically in areas where their natural habitat is small or far away (although I believe they may sometimes prefer manmade structures, especially heated structures, for better warmth and a reliable shelter).  They roost upside down because they developed wings at the expense of their ability to stand, developing specialized tendons in their feet by which they can hang effortlessly.  They can also hang from their thumbs when they need to give birth or drop waste.
http://www.derm.qld.gov.au/wildlife-ecosystems/wildlife/az_of_animals/micro_bats_the_insect_terminators/