The caterpillar begins life as a single egg or one of many tiny eggs. These eggs are called larvae. The egg can hatch quickly or stay dormant for as long as two years. When the caterpillar hatches, it will grow many times and shed its skin repeatedly, while eating many times its body mass. When the caterpillar is ready to take on the next stage, it spins silk and turns into a pupa. This begins the resting stage which usually lasts 10 days to two weeks. A butterfly then emerges from the cocoon and will live out the rest of its short life drinking nectar or rotting fruit.
Butterflies and caterpillars thrive in areas with lots of sun and limited insecticides. They are found all over the country but some caterpillars travel long distances and only stay on one area for a few months at a time. The monarch is known to travel from Mexico to areas dotting the western coast of the United States. Contact your local botanical society or center for information about where to find caterpillars and butterflies in your area.
While caterpillars will probably eat any leafy green they come into contact with, species can have specific preferences. If your caterpillar is found munching on a plant outside your window, bring that plant in to add to the jar. If you find it on a non-plant surface, bring in plants from the general area it was discovered in.
Place a piece of cheesecloth over the opening of the jar to create a porous place for the caterpillar to attach to. Add twigs and leaves from the area the caterpillar was found in, and set it in a warm spot with some direct sun but not a full day's worth. Secure the cheesecloth with a rubber band to keep the caterpillar from making its home somewhere else in your environment.
This project can quickly become something for a whole classroom to enjoy and participate in. Mail order caterpillars will deliver caterpillars right to your classroom and each child can take an active role in creating the environment and writing down their caterpillar's progress as it grows and changes.