The way a caterpillar looks determines which kind of butterfly it will become. Likewise, the plant on which you find the caterpillar can also help you determine which type of butterfly it will turn into. This is because many types of caterpillar only eat one kind of plant. Others might eat more than one kind, but all caterpillars are selective in what they eat.
Some caterpillars prefer the leaves found on specific trees for their food. These caterpillars might only eat from one specific tree, or they might prefer one of several trees. For instance, the eastern tiger swallowtail shows little preference for particular trees. Instead, these caterpillars enjoy any broadleaved tree. However, the mourning cloak will only eat from poplar, willow and elm, while the viceroy shares the preference for poplar and willow, but enjoys aspen, plum, cherry and apple trees as well.
Flowers are the favourites of some species of caterpillars. While the flowers do not always offer many leaves for the caterpillars, they are often found in groups, which can supply enough food for a hungry caterpillar. Some of the caterpillars that enjoy flower leaves for food include: the fritillary butterfly species, which enjoy violets; the zebra longwing, which eats the leaves of passionflowers; and the buckeye, which seeks out snapdragons and many other garden flowers.
Many garden plants are known to attract butterflies to lay their eggs. Some caterpillars will only eat the leaves of vegetable plants and other plants found in your garden or out in a meadow. For instance, the anise and eastern blacktail swallowtails enjoy carrot tops, parsley, dill and fennel. The grey hairstreak caterpillars enjoy eating cotton, strawberry, legume and mint plants. Some of the caterpillars that live in open fields eat different types of sorrel, clover and alfalfa.
All living things require water to survive and caterpillars are no different. However, caterpillars do not drink water. In fact, they do not drink at all. While butterflies drink nectar from flowers for hydration, caterpillars receive all of their hydration from the plants that they eat. If you are raising caterpillars in a jar or butterfly home, you might want to add a couple drops of water to increase the hydration in the leaves.