Many years ago, when I was way too small to remember anything, we had a neighbor who was a respected journalist for one of the Lancaster papers. He also was Lancaster County's acknowledged leading woolly bear prophet.
If you don't know about the woolly bear, welcome to the country. It's time you found out. It's that fuzzy, but bristly, little (maybe two inches long) caterpillar that seems to be everywhere in the fall. Color ranges from light tan to totally black or a mixture thereof. The color is where the prophecy begins. Black indicates a cold winter. Tan or brown indicates a mild winter. With that information it not too hard to figure out that if it's black on both ends and brown in the middle the winter starts and ends cold with a mild stretch in between.
My childhood prophet had no trouble with the fact that there are some of both colors every season. He was quite content to accept the majority opinion offered by the colors after viewing lots of woolly bears.
The woolly bear really is the larvae of the rather insignificant Isabella moth, which often flutters unnoticed toward our outdoor lighting from April to August. There are two generations, one in May and one in August. I'll come back to that.
Young caterpillars feed on a number of weeds like nettles, plantain and dandelions. Other favored food plants are grass, asters, sunflowers, and birch, elm and maple trees.
I threw in the last paragraph because it's true not because it really matters. No one will ever notice any damage.
Without a bit of research I would never have realized that there was a spring generation. The May hatch lives its full life cycle that year. The fall hatch over-winters wherever they can find cover, wake up in the spring and continue the cycle.
My belief is that we see tons of them in the fall, but only a few survive to produce the spring generation. Those few that make it to moths produce enough eggs to produce a large population in the fall.This little critter has no importance and appears quite fragile. However, it is well known and probably is the most visible of many insect species that are out there but seldom recognized, Caterpillars are near the top of things easy to kill with chemicals.
My message is that before you spray, give it some thought and target the problem rather than being indiscriminate killing dozens, if not hundreds and probably thousands of little critters that are of little significance other than that they exist.
By the way, research indicates that the age of the caterpillar and the level of moisture in its environment determine its color. Don't you just hate it when research interferes with what you have always known?