Excerpted from De proprietatibus rerum 12.38

The bat (vespertilio) gets its name from the time of day, because it flees the light and flies around in the evening (vespertinus) dusk with its rapid motion checked, suspended on the delicate membranes of its arms. It is an animal like a mouse, sounding not so much like a voice as a whistle. Its appearance is at once like a bird and like a quadruped, and is rarely found among other birds. Thus far Isidore [Etymologies 12.7].

original latin

Dicit etiam glossa super Is. capite 2 [Isaiah 2:20, cf. Jerome, Glossa super Isaiam], quod vespertiliones lucem fugiunt, caeci enim sunt sicut et talpae. Pulverem lingunt, oleum de lampadibus sugunt, in rimulis parietum se abscondunt. Frigidissimae sunt naturae, unde sanguis vespertilionis linitus super palpebras non sint recrescere pilos, ut dicit Constantinus [Africanus, Pantegni], et hoc forsan est quia sua frigiditate opilat poros, quibus opilatis non recrescunt pili.