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Calomys callosus - Large Vesper Mouse


Calomys callosus is the largest species in the genus Calomys.  The large vesper mouse is a generalist species.  They are dark gray-brown on the dorsal surfaces and gray on the ventral surfaces.  The tail is sparsely haired and bicolored.  The vesper mouse has tan feet and large prominent ears.  The total body length is 60-125 mm and the tail length is anywhere from 30-90 mm (Nowak 1999).  The tail is usually shorter than the head and body.  Their teeth are low-crowned.  The chromosome number of the Calomys callosus is 2N=36, FN=48 (Bravo et al. 2001).  Large vesper mice have either 8, 10 or 14 mammae (Nowak 1999).


Calomys callosus is widely distributed across South America from Argentina to eastern and southwestern Brazil and into Paraguay.  They are one of the most widespread genera of the Neotropical rodents (Bravo et al. 2001). 

Ontogeny and Reproduction:

Females undergo post-partum estrus, which lasts for approximately 6 days.  After a 21.8 day gestation, they have a litter of 4-5 young.  The offspring weigh approximately 2 grams at birth.  The babies are weaned at 15-21 days, and sexual maturity is reached when the mouse is 45-50 days old (Nowak 1999, Redford and Eisenberg 1992).

Ecology and Behavior:

Calomys callosus are a nocturnal species that tend to live in montane grasslands, brushy areas, and forest fringes (Nowak 1999).  In Paraguay, the large vesper mouse is found in palm savannas, bunchgrass meadows, and dry marshes (Redford and Eisenberg 1992).  They shelter in bunchgrass, holes in the ground, rotting tree stumps, and among rocks.

Calomys callosus are opportunistic of fire in open pasture habitats (Briani 2004).  When pasture fires occur, they are one of the first species to recolonize the area.  The vesper mouse is able to adapt their diet to include more invertebrates, which are more readily available after a fire (Briani 2004).  While the large vesper mouse is primarily an insectivore that feeds on arthropods, they also feed on plant material.


Calomys callous was identified as the rodent reservoir of the Machupo virus, which causes BHF, or Hantavirus (Dragoo et al. 2002).  BFH is a disease endemic to Bolivia.  Because of their unique DNA sequence, the large vesper mouse failed to develop antibodies against the virus.  The virus is transferred from mouse to mouse venereally as well as through wounds sustained during intraspecific fighting (Johnson 2004).  Humans contract BHF through the inhalation of aerosolized virus, bites from infected mice, or through contact with the urine, saliva, or droppings of infected mice (Johnson 2004). 

Literature Cited:

Bravo, J.S., Dragoo, J.W., Tinnin, D.S., Yates, T.L.  2001.  Phylogeny and Evolution of the Neotropical Rodent Genus Calomys:  Inferences from Mitochondrial DNA Sequence Data. Academic Press.  Molecular Polygenetic and Evolution 20(2):173-184.

Briani, D.  2004.  Fire and Small Mammals.  Institution of Conservation Biology. Accessed 1 December 2004). 

Dragoo, J. W., Bravo, J., Layne, L. J., and Yates, T. L.  2002.  Relationships within the Calomys callosus species group based on amplified fragment length polymorphisms.  Biochemical Systematic and Ecology 31:703-713.

Johnson, K.  2004.  The Discovery of Hantaan Virus: Comparative Biology and Serendipity in a World at War.  Journal of Infectious Diseases 190(9):1708-1722.

Nowak, M.  1999.  Walker’s Mammals of the World, 6th Edition, Volume 2.  Johns Hopkins University Press. pp 1402-1404.

Redford, K. and J. Eisenberg.  1992.  Mammals of the Neotropics the Southern Cone, Volume 2.  The University of Chicago Press.  pp 278-279.

Reference written by Desiree Dahl, Biol 378 (Mammalogy), University of Wisconsin – Stevens Point:  Edited by Chris Yahnke. Page last updated 07-25-05.

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