The caatinga vesper mouse (Calomys expulsus) (also known as the caatinga laucha[2] or rejected vesper mouse[1]) is a rodent species in the family Cricetidae from South America.

[2] It is endemic to eastern Brazil, where it is found in open savanna (cerrado) and thorny scrub (caatinga) habitats.

[2] Karyologic analysis of C. expulsus has shown that the X chromosome is large and submetacentric while the Y chromosome is either acrocentric or submetacentric.

[3] Predators include the barn owl .

[4] Sexual dimorphism in shape and size occurs; the former is present mainly before the age of 20 days.