There are an astounding 180,000 different species or types of caterpillars. Most of these types are not harmful but some types wreak havoc on crops and trees and can do great damage to property. People are fascinated with these little insects and although a few types may be unattractive, some are down right beautiful.Caterpillars are the larva of either a moth or a butterfly. This means that they transform into these new insects. When they are ready to do this, they will find an undisturbed area up in a tree and build a cocoon around themselves. Caterpillars have a silk stranding that is called a spinneret. It lets this silk stranding go when it walks and uses it to swing or drop. This is similar to a spider but the caterpillar also uses this stranding as a wrap, for the outside of its cocoon.