An egg is laid on the underside of a leaf. It appears to look like a small green translucent marble. Preschooler's attention would be engaged right away, if the teacher were to make a game of finding the egg under a leaf. Make leaves out of green construction paper and have the preschoolers turn them over to find the "egg" -- a small green bead -- you have colored or glued to the back of a single leaf. If you have room for a display in your classroom, get an artificial tree, and glue a marble to the underside of one leaf. Tell the preschoolers that the egg has been laid in a secret spot and have them look for it individually. Another idea is to draw a mural of a tree and give each child an outline of a leaf to color and cut out. Have them glue an egg to the back of their leaf. Attach each leaf to the tree at the stem with tape or tacks, so that the underside can be lifted.
The caterpillar emerges from the egg in the next stage of the life cycle. In order to illustrate that, draw a fat caterpillar with lots of sections that the preschooler can color. Encourage them to use their favorite colors on the caterpillar, while explaining that these colors will be similar for the butterfly. Or, draw a poster size outline of a caterpillar and let each child color in a section. Hang this next to the artificial tree. If you have done the tree mural, cut out individual caterpillars that are smaller than the leaves. Have the children color their caterpillars and then attach them to the leaves.
The caterpillar wraps himself in a cottony cocoon called the chrysalis to undergo the process of metamorphosis that will turn it into a butterfly. Demonstrate the size and shape of the chrysalis. Have the children paste cotton to a simulated caterpillar, which can be formed of clay or crayon pieces. Attach the chrysalis to the branches of the tree. You can also make up a little song about the caterpillar sleeping through the winter.
Have each child color a butterfly and cut them out. Hang the butterflies with thread from the ceiling, so that they can appear to be flying in the breeze, or tack them to the wall by the tree mural. Point out the differences between some of the colorings of the butterflies, explaining that nature provides us with many different colors and types of butterflies.