Temperature constrains the kinetics of enzyme-catalyzed reactions and shapes the performance of whole-organism physiology and life history traits. Additionally, the environmental temperature can set the boundaries to a species’ distribution and abundance. Therefore, an integrative understanding of the mechanisms by which an organism can adjust its physiology and life history in response to thermal changes, is crucial to advance our knowledge of the observed ecological patterns. In this context, due to their phylogenetic and biogeographical history, New Zealand stick insects are an ideal study model. Despite their tropical ancestry, they occur on a wide altitudinal and latitudinal gradient, encompassing different temperate and alpine habitats. Here we estimate the thermal sensitivity of digestive efficiency and quantify the thermal reaction norm of growth rate and size at maturity, among different species of New Zealand phasmids. The preliminary results show that proteins are absorbed more efficiently around 10°C. This is consistent with the hypothesis that cold temperatures slow down the transit of food along the gut, allowing more time for digestion. On the other hand, among the four species studied, only Acanthoxyla geisovii reaches a larger size at maturity when its development take place at a colder temperature than individuals reared at a warm temperature. These results give valuable insights into the evolution of different life histories and physiological strategies that allowed stick insects expand their tropical ancestral habitats to temperate ones.