The social structure of banana bats (Neoromicia nanus) was studied in relation to reproductive events over an annual cycle in banana plantations in Mpumalanga Province, South Africa. Banana plantations were visited at monthly periods over a year, and social group composition was investigated. Group composition varied considerably over the annual cycle, and was linked to reproductive status. Mixed-sex groups began to form during February, lasted until October, and were most frequent during mid winter (July). During the lactation period (Oct-Jan), females formed maternity colonies composed of lactating females and juveniles. Three kinds of leaf tubes were identified according to the size of the opening: small (0-20 mm), medium-sized (21-115 mm) and large (115 mm-unfolded leaf). Bats occupied mainly medium-sized leaf tubes. Average daily temperatures were high, even during the winter period (Jun-Aug), with humidity in the leaf tubes > 80% throughout the year. Although high humidity may play a role during hibernation to restrict dehydration, low ambient temperatures are important to sufficiently lower their body temperatures in order to lower metabolic rate and thus reduces energy requirements.