PSA: Hickory Tussock Moth caterpillar

I interrupt the irregularly unscheduled programming of this blog to offer up a Public Service Announcement about a caterpillar that has been generating lots of questions and comments of late.

The fuzzy bag of goo in question is, as shown above, the caterpillar of the Hickory Tussock Moth (HTM), Lophocampa caryae. I've received more than a few queries about these hirsute white cats, and so have many others. Perhaps you've seen one or many yourself this summer.

While the HTM caterpillars are often seen alone and on the march, they are sometimes found twisting in the breeze, suspended by a silken belay line suspended from the overarching foliage. This probably happens when some leaf-going threat startles the cat and it drops from the leaves, catching itself in midair with its strand of silk. Or perhaps it is just (literally) hanging out. Some caterpillars avoid potential predators amongst the leaves by whiling away the time dangling aloft.

When seen marching across the ground, seemingly with a purpose, the caterpillar is probably near ready to enter the pupa stage and is looking for a good spot to build and secrete its cocoon. HTMC's overwinter in their cocoon phase, hidden in leaf litter.

In their early instars (growth stages), HTM cats are conspicuously gregarious. As they mature, because they're feeding in close-knit quarters, the caterpillars can cause noticeable leaf damage. Even so, the defoliation is usually limited to a small section of whatever plant it is that they're feeding upon. I found the animals above last Sunday snacking on an oak, and even though the cats were plentiful, their damage was quite localized.

HTM cats are highly polyphagous - they can and will eat nearly any type of woody plant. Oaks and hickories seem to be preferred, though. It's common to find a resting group tightly packed together and nearly covering the entire lower surface of a leaf. The cats above, which I also found last Sunday, were on Flowering Dogwood, Cornus florida.

This species has distinct boom and bust years, and at least in central Ohio this is decidedly a boom year. Rare would be the trip afield, right about now, where a sharp-eyed observer would not see some HTM caterpillars. Nothing to be alarmed at, though, as they'll not do any lasting damage to the trees, at least insofar as I'm aware. But do be aware, sensitive people can receive a rather nettlelike rash from handling the caterpillars. The effects are normally mild and fade fairly quickly. A good rule of thumb with caterpillars is to NOT HANDLE them, especially hairy or spiny species. Many species, such as this one, are armed with stinging hairs as a predator deterrent.

The mortality rate of HTM caterpillars is extreme, and only a tiny percentage of the crop will make it all the way through to the adult stage. Those that don't become food for legions of predators, thus playing a pivotal role in the vast and complex food web. The ones that do make it through the entire life cycle will become the beautiful animal above: a Hickory Tussock Moth.

Some ordinary but extraordinary caterpillars

I am infatuated with caterpillars. The more that I learn about them, the more I realize just how vital butterfly and especially moth larvae are to the natural world. Without them, we'd lose most of our songbirds, plant communities would fall into collapse, and many of the things that we - Homo sapiens - use and need would be lost.

Besides all of that, they're just plain cool. Tubular works of art, in many cases.

Expert photographer Jack Hoying sent along some incredible shots recently, and gave me permission to share them. We'll get to Jack's stuff soon, but first a few cat shots of my own, from recent excursions.

I engaged in a brief botanical expedition this morning with botanists Dan Boone, Andrew Lane Gibson, and Brian Riley. Part of the trek meant bushwhacking through a thickly overgrown meadow. I was pleased to glance down at one point, and see that I had picked up a hitchhiker. This gorgeous caterpillar, Cucullia asteroides, which goes by the curious common name "the asteroid", was riding along on my leg.

Not one to let a photo op pass by, I placed the asteroid on some plants more friendly to its tastes than Levi's denim, and snapped a few images. This is a large colorful animal that feeds primarily on goldenrods, asters, and perhaps other members of the composite family.

While up in northern Michigan leading my NettieBay Lodge expeditions a week or so ago, we had stopped at a quiet pine-filled campground one day for lunch. A few of our party were sitting at the base of a red pine when they heard a soft thud, and looked down to see this interesting caterpillar. It had fallen from the tree for some reason, but its tough luck was our good fortune. Note its pinkish-rosy belly, and had you been there, you would have seen how the caterpillar thrashed violently side to side when handled.

It turned out to be the larva of the Ilia underwing moth, Catocala ilia, and it was quite unharmed. The cat quickly climbed back up the trunk of the pine a few feet, then froze in place. This is not a small caterpillar - two or so inches in length - but look how well it blends with the bark. Ilia underwing caterpillars, at least in some forms, are lichen mimics and this one surely does match the lichen-encrusted bark very well.

Photo: Jack Hoying

Now to Jack Hoying's incredible images. You may have seen the moth above before, perhaps around night lights. It's a hickory tussock moth, Lophocampa caryae, and they're quite common. But you'll seldom see images of this quality, of any moth. Jack happened along and caught the moth in the act of laying her eggs on this oak. How many eggs do you think there are? More than you might guesstimate, I'd bet - probably a few hundred.

Many moth species essentially carpet-bomb the foliage with their eggs. Caterpillar predators are so varied and prolific that producing scads of eggs is the only way of ensuring that one or a few make it to the stage of the flighted adult and reproductive maturity.

Photo: Jack Hoying

Jack went out to investigate the tussock moth's nursery leaf last night, and it turns out he timed his visit beautifully. He caught the tiny caterpillars just as they had emerged from their even tinier jewel-like egg cases.

Photo: Jack Hoying

At this early stage, the caterpillars are said to be in their first instar. They'll molt several times before reaching maturity, and after each shed will emerge larger. But with each passing instar stage, their ranks will be greatly reduced. Birds, parasitoid flies and wasps, and other predators will pick them off. Caterpillars are Nature's hotdogs - prime sources of protein for all manner of animals, including those warblers that we all know and love.

Jack's photo series is amazing; a captivating window into a little-seen forest animal. But hickory tussock moths are abundant, and this scene plays out millions of times each summer throughout Ohio. Most of us just never notice.

I took this photo of a fully grown hickory tussock caterpillar a few years ago in southern Ohio. It is hundreds of times larger than the fry that Jack photo-documented, and with luck, a few of the animals in his photos will reach this stage.