Nature: Seldom-seen caterpillars vital link in food chain

Jim McCormac

Caterpillars represent the vast underworld of the food chain. Out of sight and out of mind, they make the natural world go ’round.

Trick question: What’s the biggest group of herbivores (by biomass) in Ohio? No, not white-tailed deer. Caterpillars. All our state’s deer would make a big heap. Pile up all of the caterpillars, and that stack would dwarf the deer.

So why don’t you see many, if any, caterpillars? After all, these larvae of butterflies and moths are fantastically diverse, with a collective 2,000-plus species in Ohio.

Short answer: They’re very good at hiding. But caterpillars are prolific and everywhere, especially in wooded areas.

I’ve been stalking caterpillars with a camera for years, and have made thousands of images of them. The vast majority were taken at night. Like a hidden army, caterpillars emerge from hiding spots under cover of darkness, the better to avoid predatory birds, insects and other diurnal predators

Caterpillars have evolved a large, diverse bag of tricks to avoid predators, but literally tons are still found and eaten. Experts think the mortality rate hovers at about 99 percent. Thus, most moths and butterflies engage in carpet-bombing reproduction. One female might lay hundreds or thousands of eggs. Such prolificacy is necessary to get a few through the predatory gauntlet and to the adult-reproductive stage.

The fallen caterpillars did not perish in vain. Birds galore, other insects, and even mammals made meals of them. Caterpillars underpin food webs, and without them we would lose many of our higher animals. The plants that are eaten by caterpillars — which is all of our native species — would go haywire.

Some of these crawling tube steaks are especially impressive, and I recently encountered a Holy Grail. While on a southern Ohio excursion, an exceptionally keen-eyed friend, Molly Kenney, spotted a hickory horned devil 12 feet up in a black-walnut sapling

Our group gathered to marvel at the hotdog-sized behemoth. We eventually extracted the horned devil from its tree for photos. Fierce as it looks, horned devils are harmless. The orange-and-black spines do no damage, nor does it bite.

However, the shock-and-awe factor probably sends most songbirds fleeing.

Eventually, hickory horned devils come to the ground of their own volition and roam about searching for soft earth. This is when people most often encounter them. Once a suitable site is found, the devil will burrow in and form a subterranean pupation chamber in which it spends the winter

Come spring or summer, the adult moth, which is known as a royal walnut moth, will push from the ground. The adult moth is bat-sized, orange-brown and as spectacular as its larva. Unlike its gluttonous caterpillar phase, the moth does not feed, lives but a week or so, and exists only to find a mate and reproduce.

Hickory horned devils are an important part of the ecology of hickory, sweetgum, walnut and a handful of other trees. Most other caterpillars are tightly wedded to a small suite of plants that are indigenous to their area; they will eat nothing else.

Caterpillar production is a huge part of why conservation of native plants is vital — they serve to fuel much of the rest of the food chain. Nearly all caterpillar species shun non-native flora. By planting native species in your yard, you can help generate little sausages for birds and other critters.

Naturalist Jim McCormac writes a column for The Dispatch on the first, third and fifth Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com.