Bees show limited ability to acclimate to heat stress, which has implications for their survival in the face of climate change. Researchers studied six bee species from the Greek island of Lesvos, measuring their critical thermal maximum (CTMax), the temperature at which they lose motor control. They found that CTMax varied among species and increased with body size, but acclimation to higher temperatures did not significantly increase CTMax in most species. The acclimation response ratio, a measure of how much CTMax increases with acclimation, averaged 9% across species and was not significantly related to body size or CTMax. Additionally, acute heat exposure did not lead to a significant increase in CTMax. These findings suggest that bees have limited physiological capacity to enhance heat tolerance through acclimation or in response to prior heat exposure, making them vulnerable to rapid temperature changes during extreme weather events. The study highlights the weak plasticity of CTMax in insects, emphasizing the importance of behavioral thermoregulation for avoiding extreme temperatures. Conservation efforts should focus on preserving native vegetation to provide bees with temporary thermal refuges during extreme weather events. The results indicate that bees may not be able to adapt quickly to changing temperatures, and further research is needed to understand their responses to varying acclimation conditions and to assess the thermal tolerance of immature stages.Bees show limited ability to acclimate to heat stress, which has implications for their survival in the face of climate change. Researchers studied six bee species from the Greek island of Lesvos, measuring their critical thermal maximum (CTMax), the temperature at which they lose motor control. They found that CTMax varied among species and increased with body size, but acclimation to higher temperatures did not significantly increase CTMax in most species. The acclimation response ratio, a measure of how much CTMax increases with acclimation, averaged 9% across species and was not significantly related to body size or CTMax. Additionally, acute heat exposure did not lead to a significant increase in CTMax. These findings suggest that bees have limited physiological capacity to enhance heat tolerance through acclimation or in response to prior heat exposure, making them vulnerable to rapid temperature changes during extreme weather events. The study highlights the weak plasticity of CTMax in insects, emphasizing the importance of behavioral thermoregulation for avoiding extreme temperatures. Conservation efforts should focus on preserving native vegetation to provide bees with temporary thermal refuges during extreme weather events. The results indicate that bees may not be able to adapt quickly to changing temperatures, and further research is needed to understand their responses to varying acclimation conditions and to assess the thermal tolerance of immature stages.