Myotis horsfieldii belongs to the subgenus <Leuconoe> and is particularly similar to Myotis Horsfieldii, except that the pterygodes of the lesser megapodes end at the ankle, whereas the pterygodes end at the base of the metatarsal bone. The former has a wider skull and stronger teeth than the latter, with longer upper canine teeth, larger first premolar teeth, and wider upper molar crowns, but the upper molar teeth of both species are typical of Myotis.
In Thailand, both sexes live in small groups. In mangrove habitats, the bat flies low to the water surface to both prey on flying insects and pick up surface insects. The hind legs are relatively strong, presumably feeding on small fish on the surface. Since the use of strong hind feet for fishing has been demonstrated in studies of big-footed Myoetis bats, it remains to be further verified whether smaller giant bats also use their more developed hind feet for fishing.