Whether a butterfly's body can function depends heavily on the weather. Strong winds and raindrops can damage butterflies' wings. Since butterflies have no way to repair wing damage, they usually find shelter when they sense changes in the weather that signal an oncoming storm. But temperature can be an even greater threat than rain or hail.
Butterflies' bodies work best at an internal temperature of about 82 degrees Fahrenheit (28 degrees Celsius). Butterflies can't move their wing muscles at all if they get too cold, which means they can't look for food or flee from predators. Many butterflies use the colors on their wings as a warning to predators -- they quickly flash bright colors or vivid, eye-like designs to startle a predator, and then they fly away. Butterflies can also show their colors to warn predators of their chemical defenses, such as toxins or foul-tasting compounds. In very cold weather, butterflies can't do any of this.
Unlike mammals, which can usually keep their temperature steady in all but extreme temperatures, butterflies have to use their surroundings to manage their body heat. And staying warm can be tricky. At night, butterflies roost, or take shelter, to protect themselves from the drop in temperature, but daytime is a different story.
During the day, you may see butterflies basking with their wings open to catch the warmth from the sun. In chillier temperatures, butterflies can also use their wings as reflectors, opening them partially to focus the sunlight onto their thorax, where their wing muscles attach. Sometimes, butterflies will rest on warm rocks to soak up the heat from underneath. If the weather gets too warm, a butterfly may fold its wings flat and arrange itself so the sun hits the narrow edge of its wings rather than the broad side.
Sometimes, the sun doesn't provide enough warmth to get a butterfly moving. When this happens, the butterfly can move its wings in tiny increments in each direction, gradually warming the muscles. This movement is a lot like how your body shivers in cold weather to keep you warm. Eventually, the butterfly's muscles warm up, and it's able to fly.
A butterfly doesn't get to stop worrying about temperature once it's in the air. Butterflies' bodies get colder as cool breezes move over them, just like a hot spoonful of soup cools off if you blow over its surface. This is why butterflies often fly in short, rapid bursts on very cool days. A butterfly will warm itself until it's ready to fly, move quickly to the next flower or basking spot, and begin warming itself again.
Not all butterfly journeys involve short hops from flower to flower. More than 200 butterfly species migrate over long distances. The most famous is the monarch butterfly, which makes its journey to overwintering grounds in California and Mexico in several stages involving multiple generations of butterflies.
To make such a journey, butterflies have to eat lots of food and store lots of energy. On the next page, you'll learn more about what butterflies eat, including why their tendency to drink from shallow puddles isn't just about the depth of the water.