However, its brown fur is distinctive and it is clearly different in characters of its karyotype and DNA sequences.

With a forearm length of 30.8 to 34.6 mm (1.21 to 1.36 in) and body mass of 3.5 to 5.5 g (0.12 to 0.19 oz), Myotis alcathoe is a small bat.

The IUCN Red List assesses Myotis alcathoe as "data deficient", but it is considered threatened in several areas because of its rarity and vulnerability to habitat loss.

[3] In 2001, the species was described by German zoologists Otto von Helversen and Klaus-Gerhard Heller on the basis of specimens from Greece and Hungary.

[4] Although it also differs from other whiskered bats by morphological characters, Myotis alcathoe is most clearly distinct in its genetics, including DNA sequences and the location of the nucleolus organizer regions.

[5] Two studies used microsatellite markers on European whiskered bats: the first one used western European samples and recovered three well-defined species clusters for M. alcathoe, M. brandtii and M. mystacinus;[6] the other one, conducted in Poland, suggesting a high level of hybridization with other whiskered bats that would further complicate attempts to identify M. alcathoe morphologically.

It is morphologically difficult to distinguish from M. alcathoe, but sufficiently distinct genetically to be considered a separate species.

[18] However, none of the classical sources speak of Alcathoe as a nymph; instead, she was a princess, the daughter of King Minyas of Orchomenos.

[1] The name of the subspecies M. a. circassicus refers to Circassia, a historical region of the northwestern Caucasus.

[22] The brown fur distinguishes adult M. alcathoe from other whiskered bats, but juveniles cannot be unambiguously identified on the basis of morphology.

[24] On the upper side of the body, the hairs are 6 to 8 mm long and have dark bases and brown tips.

The tail extends only about 1 mm beyond the back margin of the uropatagium (the portion of the wing membrane between the hindlegs).

[33] The skull is similar in shape to that of M. mystacinus and M. brandtii, but the front part of the braincase is higher.

[29] The Caucasus subspecies, M. alcathoe circassicus, has a relatively narrower skull and longer upper molars.

B") differs from both M. mystacinus and M. brandtii in the pattern of active nucleolus organizer regions on the chromosomes.

[5] M. alcathoe also differs from other Myotis species in the sequences of the mitochondrial genes 12S rRNA and NADH dehydrogenase subunit 1 by at least 5% and 13%, respectively.

[15] Although Myotis alcathoe was initially known only from Greece and Hungary and was thought to be restricted to southeast Europe, records since then have greatly expanded its range, and it is now known from Portugal, Spain and England to Sweden and European Turkey.

[44] In the south of the continent, it usually occurs in mountain ranges, but the factors affecting its distribution in the north are less well known.

[45] Although there are abundant records from some areas, such as France and Hungary, the species appears to be rare in most of its range.

[106] According to a study in the Czech Republic, the diet of Myotis alcathoe mostly consists of nematoceran flies, but caddisflies, spiders, small lepidopterans, and neuropterans are also taken.

Most of the tree roosts were in oaks (Quercus robur); others were in limes (Tilia cordata), birches (Betula pendula), and various other species.

[7] In Saxony-Anhalt, the species forages deep in valleys when temperatures are above 10 °C (50 °F), but on warmer slopes or rocky areas when it is colder.

[115] There, M. alcathoe is relatively easy to capture in August, because M. brandtii and M. mystacinus already start swarming in late July.

[120] A study in Poland suggested frequent hybridization among M. alcathoe, M. brandtii, and M. mystacinus sharing the same swarming sites, probably attributable to male-biased sex ratios (1.7:1 in M. alcathoe), a polygynous mating system, and the high number of bats at swarming sites.

[121] M. alcathoe showed a particularly high proportion of hybrids, perhaps because it occurs at lower densities than the other two species.

[118] Reservoir construction may threaten the species' habitat in some places; two Greek sites where it has been recorded have already been destroyed.