Hairy-tailed Bolo Mouse

The Hairy-tailed Bolo Mouse is a small terrestrial rodent native to the open grasslands and savannas of central South America, especially the Brazilian Cerrado. It is one of the most abundant small mammals in its range and plays a key ecological role as prey for many predators. The species is notable for its adaptability to disturbed and agricultural habitats, making it a common study subject for hantavirus and rodent-borne disease research.

Central and eastern South America, primarily Brazil, with range extending into Bolivia, Paraguay, and northern Argentina

Widely distributed across central Brazil (Cerrado and adjacent biomes), extending into eastern Bolivia, Paraguay, and northern Argentina, with the core of its range in the Brazilian highlands.

Altitude and depth

Typically found from near sea level up to about 1500 meters elevation

Seasonal movements

Reproductive activity and population density fluctuate seasonally, often peaking during and after the rainy season when food availability increases

Primarily inhabits open grasslands, savannas (especially Cerrado biome), and shrublands; also found in agricultural fields, pastures, and secondary growth areas with dense grass cover.

Adaptations to its environment

Possesses a robust, compact body suited for burrowing and moving through dense grass; its diet flexibility and high reproductive rate allow rapid population recovery after disturbances such as fire, which is common in Cerrado ecosystems.

Listed as Least Concern by the IUCN due to its wide distribution, large population, presumed large overall population, and tolerance of habitat modification.

Estimated population

No precise global population estimate exists, but the species is considered abundant and common throughout its range with a stable population trend.

Habitat conversion for agriculture and cattle ranching in the Cerrado, though the species often persists or even benefits from such disturbed habitats; localized threats include pesticide use.

Diseases and parasites

Known to be a natural reservoir for hantavirus (including Araraquara virus), as well as host to various ectoparasites such as mites, fleas, and ticks.

No species-specific conservation programs exist; benefits indirectly from protected areas within the Cerrado biome such as national parks and biological reserves.

Recommended actions

Continued monitoring of Cerrado habitat loss, maintaining protected grassland areas, and further research into its role as a disease reservoir for hantavirus.

Has short, dense fur that is grayish-brown to reddish-brown on the dorsal side and paler, whitish-gray underneath; the tail is notably hairy, giving the species its common name, and is generally shorter than the head-body length.

Size

Head-body length ranges from approximately 80-130 mm, with a tail length of about 60-100 mm

Weight

Typically weighs between 20-60 grams, with some regional variation

Distinctive features

Distinguished from related Necromys and Akodon species by its relatively hairy tail, robust skull morphology, and specific dental characteristics used in taxonomic identification.

Differences between males and females

Minimal sexual dimorphism; males and females are similar in size and coloration, though males may be slightly larger on average.

Generally solitary or loosely social outside of breeding periods, though population densities can be high in favorable habitat, leading to overlapping home ranges.

When it is active

Primarily nocturnal and crepuscular, though some diurnal activity has been documented depending on predation pressure and season.

Diet

Omnivorous diet consisting mainly of seeds, grasses, and other plant material, supplemented with insects and other small invertebrates.

How it feeds and hunts

Forages on the ground, using its sense of smell to locate seeds, plant matter, and insects; not a specialized hunter but an opportunistic feeder.

Communication

Communicates through scent marking via urine and glandular secretions, as well as ultrasonic vocalizations typical of small rodents, used especially between mothers and pups.

Interactions with other species

Serves as an important prey species for owls, hawks, snakes, and small carnivorous mammals; competes with other small rodents for food and burrow resources in shared habitats.

Role in its ecosystem

Plays a significant ecological role as a primary prey species in Cerrado food webs and contributes to seed dispersal and soil aeration through its burrowing and foraging activities.

Breeds primarily during the wet season with gestation lasting approximately 21-23 days; litter size typically ranges from 3-6 pups, and females can produce multiple litters per year.

Raising the young

Females provide sole parental care, nursing and protecting the altricial young in a nest until weaning at around 3 weeks of age.

Maturity and lifespan

Reaches sexual maturity at around 2-3 months of age; lifespan in the wild is short, typically less than 1 year, due to high predation and environmental pressures.

Classification

Class Mammalia > Order Rodentia > Family Cricetidae > Genus Necromys > Species Necromys lasiurus

Scientific synonyms

Bolomys lasiurus, Akodon lasiurus, Zygodontomys lasiurus

Recent studies

Recent studies have focused on its role as a hantavirus reservoir in Brazil, as well as phylogeographic research clarifying its taxonomic relationships within the genus Necromys.

Genome and DNA

Karyotype studies have shown chromosome numbers varying among populations (2n commonly reported around 34-40), reflecting some degree of chromosomal polymorphism within the species.

Compared with similar species

Similar in size and habits to other Necromys and Akodon species, but distinguished by its notably hairier tail and specific cranial features; it is often confused with Bolomys species due to past taxonomic overlap.

This species was once classified under multiple different genera (Zygodontomys, Bolomys, Akodon) before molecular studies clarified its placement in Necromys; it is also one of the most frequently trapped rodents in Cerrado ecological studies, making it a model species for small mammal research in Brazil.

Where and how to see it

Best observed at dusk or night in open grassland and Cerrado habitats using live-trapping methods typical of rodent field studies; not easily seen due to its small size and nocturnal habits.

Risks to humans

Can pose a health risk as a reservoir for hantavirus, which can be transmitted to humans through contact with rodent droppings, urine, or saliva; direct bite risk is low.

Human uses

Not used commercially or traditionally by humans, but is significant in scientific research related to rodent-borne disease ecology and Cerrado biodiversity studies.