Monday, August 9, 2010

Some cool cats

At last weekend's Midwest Native Plant Conference, we had some outstanding field trips, including what may have been the world's largest singing insect walk. I'm going to post a bit more about that later.

We were indeed fortunate to have had a host of experts come to speak about many facets of native plants, including the intimate linkages between insects and plants. And on some of the field trips, we were able to observe many cool and interesting insects firsthand. A few of the coolest cats follow.

While strolling the grounds of MEEC, our conference facility, on the pre-conference field trip, we were delighted to encounter several of these lime-green beauties. This is the caterpillar of the Black Swallowtail, a striking yellow and black butterfly of open habitats such as meadows and fields. The ones that we encountered at MEEC were feeding on Queen Anne's Lace, Daucus carota, a non-native plant. Black Swallowtail larvae have managed to adapt well to plants that aren't indigenous, and are often found in gardens feeding on various members of the parsley family.

Black Swallowtail cats are wonderfully interactive, and we had some fun with them. While it is true that many caterpillars are largely defenseless bags of goo, a lot of them do have an arsenal of tricks designed to repel predators. In this case, the weaponry involves osmeteria, or small horns that the caterpillar can thrust out. These horns can be seen above, just as they emerge from the cat's body.

Tapping the caterpillar on the back elicits the defensive response, and by doing so, you'll stimulate it to quickly lunge its head back at your finger while thrusting forth the orange osmeteria. These orange horns also excrete a very foul-smelling substance, and those volunteers who we goaded into tapping the little tubular beasts learned all about this.

We are amused by this strange behavior, and other than crinkling our noses at the foul scent of the osmeteria, are hardly intimidated. But, imagine if you were a tiny chickadee or perhaps a parasitoid wasp, investigating the caterpillar as a potential meal. When the thing lunged into your face with those stink-sticks, you'd probably get the heck out of there and look for easier pickings.

Of course, Black Swallowtail caterpillars still use native parsleys, and we found this one on our post-conference field trip to Cedar Bog. It was happily feeding on Cowbane, Oxypolis rigidior, a wonderful native species of high-quality habitats.

Click on the photo to enlarge it. The "face" of the caterpillar suggests some sort of dog, with nose and eyes, and tiny paws below.

While strolling around MEEC, we encountered a lush patch of Spicebush, Lindera benzoin, an important native shrub of woodland understory. Tipped by Tara Poling, we knew to look closely for telltale rolled up leaves, and BINGO - quickly scored a young Spicebush Swallowtail caterpillar.

These caterpillars roll a leaf over them and secure it with silken strands during the day. The leaf shelters make for great hiding spots, and help keep them from the always vigilant eyes of myriad caterpillar-hunting predators.

We came back that night, and were delighted to see a larger, older Spicebush Swallowtail caterpillar feeding. For the most part, all but the most toxic caterpillars, or those heavily beset with poisonous spines, feed under cover of darkness. By doing so, they greatly reduce their chances of being eaten by a bird, or parasitized by a wasp or fly, as these types of predators are active during the day. If they are confronted, Spicebush Swallowtail cats lunge their "head" at the predator. Those giant fake "eyes" create a snake-like look and serve to spook small songbirds.

Despite a massive crowd gathered close, the cat munched away with no apparent concern. Note the large extended mouthparts, which vaccuum up the margins of the leaf with great rapidity. We came back the next night, and found this caterpillar several branches away, chowing down on a different leaf on another part of the shrub.

Probably too many gardeners detest caterpillars and the perceived damage that they cause. But in most cases, the cats probably don't cause visible damage that is readily apparent. To do so wouldn't be to their advantage, and that's probably why this one had moved to a different part of the plant the following night.

If they were to routinely create massive zones of concentrated defoliation, predators would probably soon learn to associate the damage with the presence of tasty little tubes of protein. Birds, especially, would then zero in on these sites and carefully search out the caterpillars hiding nearby.


Cathy said...

I do appreciate the condensed, useful information you provide. Never knew about the nighttime versus daytime feeding caterpillars.

Scott said...

Another photo of the spicebush swallowtail caterpillar

catlander said...

Found a caterpillar on my balcony parsley here in NYC and thanks to the picture on your blog was able to identify it. Thanks!