Questions about caterpillar identification are probably the most common questions I receive via my website. Worldwide, there are about 14,500 species of butterfly and moth caterpillars. It's not impossible to i.d. Here are a few tips to help narrow the field when you're trying to find out what species of caterpillar you've found. Make sure children are aware of this as well.
Some caterpillars can give nasty stings and cause painful skin reactions.
Some caterpillars are very picky and will only eat one or a few types of plants. Others will eat a wide variety. In some of the books and websites listed below, you can look up the name of the host plant and find what types of caterpillars eat it. Then you can look for photos or written descriptions of the species listed to see which match your caterpillar. It's usually helpful to know the common name of the plant as well as its Latin name.