As summer winds down, it’s surprising to find that insects aren’t always hiding like we might assume. In fact, some insects seem to start interacting with us even more as the calendar switches over to September. One group that we get a lot of calls about at this time of year are the caterpillars. Caterpillars are the immature forms of moths and butterflies and develop through complete metamorphosis. This means that they start as an egg, hatch into a larva (which looks radically different than the adult), pupate, and emerge as an adult. Some caterpillars overwinter as larvae, hidden in leaf litter or soil, others pupate first to wait out the cold. We start seeing more of both kinds right now, as they leave trees and plants they were feeding on and search for that perfect comfy spot. Here are just a few different species you might notice.
Fall webworms are common pests that you can find in crabapples, cherry trees, and birches (amongst others). Like their cousins, the eastern tent caterpillar, they construct large web “nests” in plants where they hide and feed. Their web building behavior is slightly different though; fall webworms build their webs over the ends of branches rather than in the branch crotches like the tent caterpillar. The fall webworm is usually white in color, with long white hairs, and orange/black bumps on their backs. As summer ends, these caterpillars can be seen leaving their web nests to find a place to pupate in the soil. For control, it is best to remove the nest by pruning or just destroying it with a stick. This exposes the caterpillars to predators and parasites.
4. Tussock moths
Tussock moths are a large group, but we can usually recognize their larvae due to the tufts (or tussocks) or hair on their bodies. Many tussock moths are on the move right now looking for an overwintering site. Some, like the white-marked tussock moth, look like they have a mohawk going down their back and are generally harmless. Others should be treated with caution. Some species, such as the hickory tussock moth, can leave pokey hairs in your skin and create an itchy rash. It is described as feeling a lot like having fiberglass stuck in you. They are not poisonous or venomous though. It isn’t always easy to tell what species of “hairy” caterpillar you are looking at, so unless you know it’s a woolly bear or other harmless species, it is best to exercise caution, lest you end up with a persistent itch!
3. Hornworm caterpillars
Hornworm caterpillars are famous for their “horn” that protrudes from their posterior. The horn doesn’t actually afford a lot of protection since they aren’t very hard, and they don’t secrete a venom; they are mostly there to confuse predators. As adults, hornworms become sphinx moths, which are also known as hawkmoths, or even hummingbird moths to some. They are fast fliers and will often visit flowers like petunias that have long corollas. In the fall, you might find hornworms, such as the catalpa worm (popular with fishers), white-lined sphinx caterpillar, or even the tobacco and tomato hornworms. If you are dealing with pest problems from those tomato feeders, you can always physically remove the caterpillars or try to use Bt products earlier in the season. Most hornworms do not require insecticidal control though.
Figure 4: A catalpa sphinx moth caterpillar, also known as a catalpa worm, displays the characteristic horn on the rear end that the group is famous for. (Photo: Jim Kalisch, University of Nebraska-Lincoln Department of Entomology)
2. Giant silk moth caterpillars
The giant silk moths are called family Saturniidae. These are not the silk worms that we use to make silk products, but the family does include some of the largest moths in the world. Here in Kentucky, you might recognize representatives, such as the luna moth or the cecropia moth. The caterpillar stage of this family is searching for a place to pupate right now. Some will spin a cocoon up in the branches of their host tree, but others will wander down and search for soil to pupate in. This includes the hickory horned devil and the imperial moth, both of which can be slightly frightening if you have never seen them before. If you see large (3 to 5 inch) caterpillars wandering in your lawn, they pose no harm to you, your pets, or your grass. Leave them be, and perhaps you will get to see a really impressive moth next year when the adults emerge.
Figure 5: Hickory horned devils feed in hickory, pecan, sweet gum, and walnut trees and have a very alarming appearance. They have no venom and the horns are for show. Next year they will emerge as the beautiful royal walnut moth. (Photo: Ronald F. Billings, Texas A&M Forest Service, Bugwood.org)
1. Wooly bears
One of the most famous caterpillars in the world, the wooly bear, is a common autumn sight. They have a dense covering of “fur” on their body and the hair is alternating bands of black, red-brown, and black. There is some classic folklore that the width of the black bands on either end can tell you how severe the upcoming winter will be. The wider they are, and the smaller the red-brown band, the harsher you should expect the weather to be. Unfortunately, this doesn’t seem to be a completely accurate measure for weather. That being said, this is an amazing insect that can overwinter as a large caterpillar and even survive being frozen. You might see large numbers of them crossing roads or paths; again they pose no hazard. Just let them through and try not to step on them. If you really want to celebrate this particular caterpillar, you should head to Beattyville, Kentucky for their Wooly Worm Festival (October 25, 26, and 27)!
Figure 6: The wooly bear is famous for their hairy coat and banding coloration. While they can’t predict the weather, they are still a fascinating insect. (Photo: Whitney Cranshaw, Colorado State University, Bugwood.org).
By Jonathan Larson; Extension entomologist