The 51 species of sac-winged or sheath-tailed bats constitute the family Emballonuridae, and can be found in tropical and subtropical regions all over the world. Emballonurids include some of the smallest of all bats, and range from 3.5 to 10 cm in body length. They are generally brown or grey, although the ghost bats (genus Diclidurus) are white.They have short tails, which project through the tail membrane, so that the latter forms a sheath.