Butterfly can't fly if body temperature less than 86 degrees

Since butterflies are cold blooded ,they do not produce metabolic heat like humans. so it is necessary for them to warm up their flight muscles. This is done by basking in the sun in order to absorb heat.Most butterflies need temperatures of at least 60-65 degrees to fly.

Metabolism is the set of chemical reactions that happen in living organisms to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments.

warm blooded animals can keep their body temperature at a roughly constant level, regardless of the ambient temperature. This involves the ability to cool down or produce more body heat. Warm-blooded animals mainly control their body temperature by regulating their metabolic rates, such as increasing their metabolic rate as the ambient temperature begins to decrease.

But since butterfly is a cold blooded insect , therefore it does not release metabolic heat to respond to the environment thats why they require basking in the sun to fly.