Both live on the eastern plains, and the western harvest mouse also inhabits the valleys of western Colorado and the San Luis Valley. These are dainty, brownish mice. The animals are so small that they often huddle for warmth. The two species are hard to distinguish, but the plains harvest mouse has a narrower black stripe on its tail and tends to have a blackish patch on the back. Plains harvest mice live in open grasslands, whereas western harvest mice like a diversity of ecosystems, including shrubby grasslands, weedy borrow pits and riparian woodland.
Harvest mice are smaller than deer mice and have grooves on the faces of their incisors.
R eproduction occurs throughout the warmer months. Females produce several litters of three to five hairless, blind young after a gestation period of about three weeks. At 3 weeks old they are weaned, and they may breed at 4 weeks of age. H arvest mice eat mostly seeds of grasses and forbs, but like many granivores they also eat some insects as available. They are active year-round.