When faced with a sudden temperature change, most animals make behavioural responses that enable them to avoid extreme or lethal conditions. Among the invertebrates and aquatic vertebrates this is the only kind of thermal adjustment. The terrestrial environment is more prone than aquatic to sh6w sharp temperature changes. Insects and reptiles which are the most successful among the terrestrial poikil6therms exhibit many complex thermal responses. Capacities for rapid and appropriate responses to temperature changes are based on well developed sensory system. For example, the infrared sense organs located in the facial pit of the rattle snake can detect even very small temperature differences (0.001 to 0.005?C) which helps them in detecting warm blooded or cool (moist) prey as well I in orienting the animals to warm or cool environments.
Many insects and reptiles bask in the sun to warm their bodies and avoid extreme heat by seeking the shade or burrowing.