Nyctomys differs from Rhipidomys in coloration, as well as in having a shorter, more fully haired tail. Female Nyctomys have four mammae. The vesper rat is arboreal, usually being found at a considerable height in trees and rarely descending to the ground. It seems to be mainly, if not entirely, nocturnal. It has been observed eating wild figs and avocados.
Individuals occasionally arrive in the United States in bunches of bananas unloaded from ships.
They reported the most common vocalization to be a faint, rapid, high-pitched musical chirp or trill. The average litter size in this colony was two young. The gestation period was 30-38 days. One female gave birth to five litters over a 7-month period. Litter size evidently varies from one to four, with two probably being the mode.