September 14, 2013

It's Cat Season!

Caterpillar season, that is. September marks the end of summer, but a bonus is that a lot of large and showy caterpillars are out and about. Some are very hard to find because they have many ways of hiding, but we have been fortunate to be out with folks who are very good at spotting them. I'm trying to get better at it--the key is recognizing their host plants and then searching with a critical eye along stems and leaves.

Caterpillars are present in all the warm months, of course. They are the mainstay of the diet of young songbirds. We associate many birds with seed-intensive diets, but they also need protein, particularly when the nestlings are developing. In fact, one source that I saw says that a single pair of chickadees must find 6000 to 9000 caterpillars to raise one clutch of young. 

A Preachy Aside: Reread that last sentence, and think about whether that chickadee family is going to do well in a yard with a lot of lawn and a few exotic shrubs, chosen because "nothing eats them". We NEED to plant native trees, shrubs and wildflowers in our suburban gardens to support these critters, if we want them (and us) to survive in a world of increasingly shrinking and fragmented natural habitat. I'll give that reference again here--read it and then get and read Doug Tallamy's book Bringing Nature Home, available here and probably at your library. He was the featured speaker at the Midwest Native Plant Conference and has a very compelling message! 

Anyway--we have been exploring a lot this summer, and particularly in the past few weeks we have spotted some pretty cool cats. Caterpillars go through several molts or instars, and later instars may look totally different from earlier ones, making identification a bit challenging. The whole metamorphosis process, especially what goes on in a chrysalis or coccoon, is mind boggling. This tubular, worm-like eating machine completely changes in every way to a winged flier able to reproduce itself. Here is a gallery of nine of these amazing critters!

First up is the Pipevine Swallowtail. The caterpillar ranges from red to black, with lots of pointy projections. The adult is stunning, with its metallic blue hindwings. The caterpillars feed on members of the Aristolochia or birthwort family--here in Ohio that mainly means wild ginger and Dutchman's Pipe, which has the odd-looking flower shown below in the upper left. 

The Spicebush Swallowtail has one of the strangest looking caterpillars, and if you were a hungry bird you would think twice about eating this fierce-looking creature. It feeds on spicebush and sassafrass, both pretty common shrubs or small trees here in Ohio, and they are great plants for the garden, too. In the caterpillar photo you can see some web-like material on the leaf. This is silk that is produced by the caterpillar to draw together leaf edges, making a sort of bivouac in which to hide during the day as an added protection against predators. Many caterpillars are most actively out and about feeding at night and they hide during the day.

Another caterpillar that hides in a self-made leafy shelter is the Silver-spotted Skipper. It is pretty common in suburban gardens, and is one of the easiest skippers to identify. The caterpillar feeds on a wide variety of plants in the legume family including Black Locust, Honeylocust and many others. Silver-spotted Skippers overwinter as a chrysalis and the adults feed on a variety of flowers, but rarely on yellow ones!

Baltimore Checkerspot is one of our most beautiful butterflies. In contrast to the Silver-spotted Skipper, the caterpillar has very specific food requirements at certain points in its development; it needs Turtlehead (pictured in the lower left corner below) which occurs in wet meadows and creeksides. The young caterpillars cluster on the plants, creating a web shelter for protection.  You can see some of the webbing in the corner of the caterpillar photo. When they are larger they leave the shelter and can feed on other plants. Most chrysalises are quite camouflaged and very hard to find; the Baltimore Checkerspot chrysalis is tiny but stunning (see the inset photo in the upper right of the caterpillar photo).

Plant some fennel or dill in your garden and you are likely to attract the beautiful Black Swallowtail. They feed on a variety of members of the carrot family as well as on an interesting plant called Garden Rue (Ruta graveolens). This rue has blue-green leaves and yellow flowers and I'm going to try to find some for next year for my garden. Black swallowtails overwinter as a chrysalis. The adult in this photo is a female; the males don't have the blue on the hindwing. 

Most of us are quite familiar with the Monarch and its dependence on various members of the milkweed family of plants. Its caterpillars consume distasteful chemicals from the milkweed which protect them from bird predation. 

Monarchs are interesting in that they are migratory; all eastern monarchs head for a small mountainous area of central Mexico in the fall. This area has been subject to logging and weather stress, and despite some protection monarchs are extremely vulnerable on their wintering grounds. Adding to their trouble is the fact that the milkweed that they depend on in the north is getting more and more scarce, thanks to widespread use of herbicides following the advent of Roundup-ready corn and soybeans.

So plant milkweed in your garden! Common Milkweed (Asclepias syriaca) is kind of a coarse plant but certainly can do quite well in a suburban garden. There are many other members of the family that are quite showy, like Butterflyweed (A. tuberosa) and Rose or Swamp Milkweed (A. incarnata).

What do you suppose those things are on the Wafer Ash tree in the photo below? It looks like a couple of birds have relieved themselves right on the leaves. 

In fact, these are Giant Swallowtail caterpillars! Birds avoid eating bird droppings, so looking like one is a useful defense. Many other organisms utilize this strategy including some spiders, some moths, and some other butterflies.

The Giant Swallowtail is our largest butterfly here in Ohio, and it feeds pretty exclusively on members of the citrus family. Surprised? Yes, we have some wild citrus plants here in Ohio, namely Wafer Ash or Hoptree (Ptelea trifoliata), and Prickly Ash (Xanthoxylum americanum). Neither is an ash and neither produces edible fruit, but both are small trees that can do well in home landscapes. In the deep south, Giant Swallowtail caterpillars can be agricultural pests on the citrus crops, but here in Ohio we don't have that problem!

Another bird-dropping mimic is the Viceroy caterpillar. The caterpillars feed on plants in the willow family, including willows, poplars and cottonwoods. The adult was thought to be a mimic, looking much like the bad-tasting monarch, but lately they are believed to be toxic themselves due to the fact that they sequester salicylic acid in their bodies from their host plants, which makes them unpalatable to predators. 

Last but not least is the Cloudless Sulphur. This cat feeds mainly on plants in the genus Senna and it is mostly a southern butterfly. Typically, Cloudless Sulphurs are seen in Ohio in late summer, when they disperse from their southern breeding grounds. There is plenty of senna to support their caterpillars, but the cats probably are unable to survive northern winters.

Caterpillars are pretty amazing, given the way they have developed chemical, behavioral and visual strategies to avoid predation, and probably use other means of which we unaware. This is just a very brief introduction to the caterpillar world and I haven't even touched on moth caterpillars which greatly outnumber those of butterflies. I'll have to save that for a future post!

For more about caterpillars, go over to Ohio Birds and Biodiversity at this link and check out Caterpillars of Eastern North America by David L. Wagner.

1 comment:

  1. Fantastic! How amazing to learn about the caterpillars that mimic bird poop. We just had a kerfluffle in Neenah, the town just south of us. They had listed milkweed as a noxious weed and told someone she'd have to cut down her nice stand of it. The butterfly lovers rose up and now the milkweed will be protected. I hope we get some in the dry drainage area they're proposing for the area across the street from us. I'll talk with the landscape person on Tuesday about plants that support caterpillars. Thanks again!