Desiccation resistance, that is, the ability to reduce water loss, is an ecologically important trait relevant to all terrestrial organisms, which may constrain species distributions. Nevertheless, relatively few studies have investigated plastic capacities in desiccation resistance. We here investigate plastic responses in body mass change, used as a proxy of desiccation resistance, to variation in temperature and relative humidity in the tropical butterfly Bicyclus anynana (Butler) (Lepidoptera: Nymphalidae). Our results indicate that butterflies acclimated to a higher (27°C) compared with a lower temperature (18°C) and a lower (50%) compared with a higher (90%) relative humidity displayed a decreased loss of body mass, and therefore likely a loss of body water (27°C: 11%, 18°C: 15%; 50% r.h.: 14%, 90% r.h.: 18%). Thus, mass loss was reduced under conditions indicating increased desiccation risk, suggesting adaptive phenotypic plasticity. Effects were most pronounced during the first 24 h after acclimation, indicating quick and transient responses to environmental conditions. As anthropogenic climate change is predicted to increase the magnitude and frequency of heat and drought periods, we argue that more studies on plastic capacities in traits relating to desiccation resistance are needed to better understand species responses.