Fainalges irritans sp. nov. (Astigmata: Xolalgidae), a new feather mite species causing deplumation in red-and-green macaws Ara chloropterus Gray (Psittaciformes: Psittacidae) in Brazil, with a key to species of Fainalges Gaud & Berla, 1963.

Feather mites (Acariformes: Astigmata) are commonly regarded as harmless ectosymbionts of birds. In some cases, however, they may cause pathological conditions in their hosts. A new species of feather mite, Fainalges irritans sp. nov., is described from green-and-red macaws, Ara chloropterus Gray (Psittaciformes: Psittacidae) in Brazil, where it is associated with skin irritation and feather loss. An updated key to males and females of the genus Fainalges Gaud & Berla, 1963 is provided, and previous records of feather mites causing injuries in birds are briefly discussed.