They are not a problem is areas with freezing winter climates. This is way too poisonous for the herb garden. Either collect them by hand at night, or sprinkle some Diatomaceous Earth over and around the plant. Also, copper snail barrier is very effective at keeping them off of plants. These are the larval stage of any butterfly or moth, and are found throughout the U.S. in many different forms, and all of them feed on plants.
Caterpillars usually begin chewing on a leaf in the center , or away from the edge of the leaf.
As the egg on the leaf hatches, the tiny caterpillar comes out and immediately begins eating the leaf. They don't crawl to the edge of the leaf to begin eating. These holes start out as tiny pinholes, and as the caterpillar grows, become increasingly larger. Firstly, let us state that if there were no caterpillars, there would be no beautiful butterflies. No monarchs, no swallowtails, etc.