Sheath-tailed bats in the microbat family Emballonuridae, such as this Raffray's sheath-tailed bat, Emballanora raffrayana, have simple, plain faces. Although many microbats have a membrane (the interfemoral membrane or uropatagium) that joins the tail to the hind limbs, some species, such as the sheath-tailed bats, have free tails like those of most mammals. It is thought that these membranes might serve to help the tail act as a rudder during flight, or as a scoop for catching insects.