Split_screen shot of American cockroaches Periplaneta americana after being chilled in refrigerator. This is a demonstration to show their cold_blooded nature. The roaches on the left have not yet warmed up, and are completely inactive. Those on the right are back at room temperature. Insects are cold_blooded, which means their body temperatures changes with the temperature of their surroundings. As such, they need an external source of heat to gain the energy required to become active. These cockroaches are not harmed in any way.