The Nature Writers of Texas

The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Sunday, July 10, 2005

Caterpillars are Truly Fascinating Creatures
by Ro Wauer

Its been said that butterflies are only caterpillars that are all dressed up! In a real sense, that is true. For butterflies are only the final product of an egg that hatches into a caterpillar that eventually enters the pupa or chrysalis stage from where the butterfly will finally emerge. Butterfly caterpillars develop a chrysalis while moth caterpillars develop cocoons. The vast majority of caterpillars that eat gardens and crops are moth caterpillars; very few butterfly caterpillars eat standard garden plants and seldom become pests.

Over the years I have photographed caterpillars when the occasion arises, especially those that are attractive or out-of-ordinary. I probably have a collection of 100 caterpillar slides without a name. There has not been an easy book to help with identification, although I have sent a few images to caterpillar specialists on occasion. But now I will have no excuse for not identifying all of my caterpillar photos, as a new book - "Caterpillars in the Field and Garden" by Thomas Allen, Jim Brock, and Jeff Glassberg - has just been published by Oxford University Press ($29.95). It contains about 125 pages filled with caterpillar photos, range maps, and narrative. And there are another 20 useful pages of butterfly "foodplants." This is an excellent, must have book!

I haven't yet gone through my slides and digital caterpillar images for identification, but with only a casual read I already know that I will be able to place all of the various subjects at least into the correct groupings, and identify the majority. For instance, swallowtail caterpillars are large and have a "fleshy, retractable organ above the head, the osmeterium, which gives off a pungent odor when everted." Whites and yellows family caterpillars are usually green and blend with the hostplant leaves, "or with colors and resting postures that resemble the flowers or seedpods of the hostplants." Hairstreak caterpillars are slug-shaped and may possess a wide range of colors, usually adopting the color of hostplant on which they are feeding. Plus, many hairstreak caterpillars are tended by ants, which stroke special glands on the caterpillar's abdomen to obtain honeydew, a sweet substance that they eat, and so they provide the caterpillar protection from predators and parasites.

Most of the brushfoot caterpillars possess spiny, branched spines on their bodies that give them a fearsome appearance and protection from predators. Brushfoot butterflies range from snouts to fritillaries to crescents to leafwings and monarchs. Many of the brushfoot caterpillars remain together until the later instars, and they have a habit of quickly dropping off the hostplant when disturbed.

Skipper caterpillars, a group that comprises a third of our butterfly fauna, normally possess "smooth bodies covered with short barely noticeable hairs. Heads are large relative to the thorax, creating a constriction between the head and the first segment." One of the more interesting features of these caterpillars is their use of shelters for protection. They may "conceal themselves in a nest of leaves created by folding the leaf over and tying it with silk or by silking together more than one leaf." Most skippers can be divided into spread-winged and grass skippers. Spread-wings generally feed on leaves of legumes, oaks and other trees and shrubs. All live in a nest made by cutting and folding over a leaf flap. Grass skippers, or the closed-winged skippers, feed on grasses or sedges, and they make nests that can be hidden in a grass clump or high on their host. One of the best examples of this type is the Brazilian skipper that utilize cannas; the caterpillar folds one of the large canna leaves, forming a tunnel where it remains during the daylight hours, but comes out to feed on the canna leaves after dark.

Butterfly eggs usually hatch within a week, and a tiny caterpillar emerges. "This voracious eating machine...rapidly increases in size... the young caterpillar outgrows its skin, which splits and is shed, revealing a new, larger, and baggier skin below. As the caterpillar grows, this process is repeated a number of times (usually 4 or 5) over the course of about 2 or 3 weeks. Each stage between shedding is termed an "instar." The full-sized caterpillar then attaches itself to a support and pupates; the hard shell becomes a chrysalis. In 1 or 2 weeks, but some may take a few months or a winter, a miraculous change occurs and an adult butterfly emerges.


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