This study investigates the latitudinal variation in thermal tolerance of insects, focusing on upper and lower lethal temperature limits and supercooling points. The research uses published data on insect cold hardiness to assess whether physiological tolerances vary with latitude, supporting Rapoport's rule, which suggests that species' latitudinal ranges increase with latitude. The findings show that upper thermal limits show little geographical variation, while lower bounds of supercooling points and lower lethal temperatures decline with latitude. This indicates that lower lethal limits vary more with latitude, providing some support for the physiological tolerance assumption of the climatic variability hypothesis. However, the study also highlights the need for coupled data on species tolerances and range size. The analysis of insect cold hardiness reveals that freezing tolerance is more common in the Southern Hemisphere, but data are limited. The study also shows that the variation in cold hardiness strategies (freezing tolerant or intolerant) is influenced by latitude, with a clear geographical component in both supercooling points and lower lethal temperatures. The results suggest that the physiological tolerance assumption is supported, particularly in the Northern Hemisphere above 20–30°N. However, the variation in physiological tolerances does not always align with the predicted direction, indicating that the assumption may not apply universally. The study also examines the partitioning of variation in cold hardiness at different taxonomic levels, finding that the majority of variation in supercooling points and lower lethal temperatures is distributed across families and genera, with less variation at the species level. The results support the idea that physiological traits are influenced by phylogenetic constraints, but the extent of this varies between different groups. Overall, the study provides evidence for the physiological tolerance assumption of the climatic variability hypothesis, particularly in the Northern Hemisphere. However, the findings also highlight the need for further research to better understand the relationship between physiological tolerances and latitudinal range sizes. The study underscores the importance of considering both physiological and ecological factors in understanding the distribution of species across latitudinal gradients.This study investigates the latitudinal variation in thermal tolerance of insects, focusing on upper and lower lethal temperature limits and supercooling points. The research uses published data on insect cold hardiness to assess whether physiological tolerances vary with latitude, supporting Rapoport's rule, which suggests that species' latitudinal ranges increase with latitude. The findings show that upper thermal limits show little geographical variation, while lower bounds of supercooling points and lower lethal temperatures decline with latitude. This indicates that lower lethal limits vary more with latitude, providing some support for the physiological tolerance assumption of the climatic variability hypothesis. However, the study also highlights the need for coupled data on species tolerances and range size. The analysis of insect cold hardiness reveals that freezing tolerance is more common in the Southern Hemisphere, but data are limited. The study also shows that the variation in cold hardiness strategies (freezing tolerant or intolerant) is influenced by latitude, with a clear geographical component in both supercooling points and lower lethal temperatures. The results suggest that the physiological tolerance assumption is supported, particularly in the Northern Hemisphere above 20–30°N. However, the variation in physiological tolerances does not always align with the predicted direction, indicating that the assumption may not apply universally. The study also examines the partitioning of variation in cold hardiness at different taxonomic levels, finding that the majority of variation in supercooling points and lower lethal temperatures is distributed across families and genera, with less variation at the species level. The results support the idea that physiological traits are influenced by phylogenetic constraints, but the extent of this varies between different groups. Overall, the study provides evidence for the physiological tolerance assumption of the climatic variability hypothesis, particularly in the Northern Hemisphere. However, the findings also highlight the need for further research to better understand the relationship between physiological tolerances and latitudinal range sizes. The study underscores the importance of considering both physiological and ecological factors in understanding the distribution of species across latitudinal gradients.