Most butterflies that live in cold climates spend the winter as caterpillars, while almost as many spend the winter as pupas. A very few species spend the winter as eggs. While so-called butterfly boxes can be attractive, and do little harm, studies have shown that butterflies do not use them in any way. Most adult butterflies drink nectar from flowers through their tongues, which function much like straws. A minority of butterflies almost never visits flowers, instead gaining sustenance from tree sap, rotting animal matter, and other organic material.
Butterfly caterpillars almost all eat plant matter.
Mainly the caterpillars eat leaves, but some species eat seeds and seed pods while others specialize on flowers. Some species, such as Gray Hairstreaks, will eat a wide variety of plants and some will eat only a single plant species. The caterpillar of one North American butterfly,the Harvester, eats aphids. Many butterflies that spend the summer in temperate North America cannot survive northern winters. Each year, as the weather becomes warmer, butterflies from Mexico and the southern United States fly north to repopulate these regions.