Final answer:
A butterfly spreads its wings in the sunlight primarily to absorb sunlight for energy, which helps to raise their body temperature for better mobility and activity due to their cold-blooded nature.
Step-by-step explanation:
A butterfly might spread its wings in the sunlight while resting to absorb sunlight for energy. This behavior helps to raise their body temperature which is essential for their mobility and activity since butterflies are cold-blooded. The warmth gained from the sun enables them to fly and seek out food or mates more efficiently. Although butterflies do use their wings for various purposes such as cooling down, defensive mechanisms, or attracting mates, the primary reason they spread them in the sun is thermoregulation. This is similar to how other cold-blooded animals, like lizards, adjust their behavior to control their body temperature.