What environmental factor acts as the main barrier preventing robust python colonization north of the subtropical zone?

Sustained freezing temperatures which are lethal to the reptiles

The geographic confinement of the known, established python issue primarily to South Florida strongly suggests the presence of a climatic ceiling for these reptiles. Burmese pythons require consistently warm conditions not just to maintain high activity levels necessary for hunting and growth, but critically, for the successful incubation of their eggs. While the species can endure brief cold snaps, sustained or regular freezing temperatures prove lethal to the snakes and prevent the formation of robust, reproductive colonies outside the subtropical zone. This temperature gradient acts as the ultimate gatekeeper, reinforcing the barrier suggested by habitat suitability maps showing potential further north but no actual established populations.