Large vesper mouse

The large vesper mouse (Calomys callosus) is a South American rodent species of the family Cricetidae.

It is found in Argentina, Bolivia, Brazil and Paraguay.

Its karyotype has 2n = 50 and FN = 66. It was formerly synonymized with C. expulsus, but the latter has 2n = 66 and FN = 68.

It is particularly notable as the vector of Bolivian hemorrhagic fever.