Oligoryzomys

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Oligoryzomys is a small group of rodents in the Cricetidae family, commonly called pygmy rice rats or colilargos. The genus has about 17 species and stretches from Mexico down to Tierra del Fuego in southern South America. They live in many habitats, including tropical and dry forests, scrublands, plantations, grasslands, farms, gardens, and even houses. They spend most of their time on the ground but can climb into vegetation.

These rodents are very small: body length about 70–110 mm, with a tail about 85–155 mm. They are greyish-brown to reddish-brown, have a pointed snout, rounded ears, and a long, hairless tail that is often longer than their body. Females have four pairs of mammary glands. They are usually nocturnal and solitary, and they feed mainly on seeds, insects, and fruits.

Taxonomically, Oligoryzomys is in the tribe Oryzomyini within the Cricetidae family. The genus is known for certain dental features and a long palate, and recent studies place it in a clade with Neacomys, Microryzomys, and Oreoryzomys.

Some species are important because they can carry hantaviruses that affect humans. In Argentina and Chile, Oligoryzomys longicaudatus and other members host Andes virus (ANDV). The viruses don’t harm the rodents, but they can cause disease in people, so these rats are a focus of disease risk monitoring.