An animal’s response to climate warming is predominantly governed by its thermal tolerance. Seasonal temperature variation may indicate the boundaries of plasticity in insect thermal tolerance, which could predict the capacity to adapt to future climates. Here, we assess the changes in thermal breadth (the difference between the critical thermal maximum (CTmax) and critical thermal minimum (CTmin)) to estimate the thermal safety margin in Ischnura heterosticta and Xanthagrion erythroneurum damselflies across different seasons. For both species, CTmax and CTmin increased with monthly temperature, with a stronger increase of CTmin in summer. Overall, thermal breadth was broad in spring and autumn (around 41 degrees) but in summer we observed a large number of individuals with substantially narrower thermal breadth (down to 26–35 degrees). Our results establish considerable seasonal thermal plasticity in damselflies, which might provide a degree of resilience in future climates, yet during the most critical season (summer), heat spikes might push a substantial proportion of the population beyond their limits.
