Things You'll Need
Instructions
Take a photograph of the caterpillar and the plant you found it on, if possible.
Note the major color of the caterpillar and any prominent secondary colors. Annotate any stripes and their direction whether along the body or around it, and spots and whether the head is a different color.
Estimate the size of the caterpillar. If you don't have a ruler, tear a piece of paper or leaf to the length of the caterpillar and measure it later. Also note the caterpillar's thickness.
Record whether the caterpillar is fuzzy, furry, has tufts or has horns and their color.
Identify the plant that the caterpillar is on. Knowing the plant can help narrow down which butterfly your caterpillar will become as butterflies pick very specific host plants to lay their eggs on.
Look at websites with pictures of caterpillars such as Bug Guide and What's That Bug (see Resources) and look for a caterpillar that matches your description. Mississippi State University also has a caterpillar guide (see Resources).
Contact a land-grant university extension in your state for assistance or investigate their online resources.
Post your photo on Bug Guide, What's This Bug, Butterfly and Moth Caterpillars: Identification Guide, or other butterfly centered sites (see Resources).
Identify the plant that the caterpillar was on and research the plant. Many plant books include the information of what caterpillars host on them.