"Nature Guide Journal"

8 June 2002

The measured motion caught my eye:  each inching step started with the caterpillar's tail end drawing forward to grasp the pine twig; the head end then letting go to stretch ahead, seeking the next place to grab.

Slightly puffed, dark creases around the caterpillar made the body seem softer, upholstered.  Tufts of dark, stiff, quarter-inch bristles lined up along the upper "shoulders."  Delicate tracings of black, brown, and yellow fit between the creases and the rows of bristles; tiny dots of pale blue trimmed out the back.

The egg that hatched this lithe caterpillar may have been laid several months ago. The length of time between egg and adult varies by species, and by the local conditions, such as temperature and food supply.

Insects approach the journey from egg to adult via two general paths: "incomplete metamorphosis," where the young look much like the adults—earwigs, for example; and "complete metamorphosis," where the young look much different from the adults—butterflies and moths, for example.

In insects with complete metamorphosis, a larva, grub, maggot, or caterpillar hatches out of the egg.  A larva's role is to eat and grow bigger.  Spreading out the impact on their habitat, the larvae eat very different food than the adults.  The caterpillars of most species of butterflies and moths will eat only a particular species of plant, usually staying on a single individual through the entire stage.

Caterpillars employ a variety of defense mechanisms to protect against being eaten: camouflage, bristles and protrusions, startling "eye spots," poison, offensive smell or taste, or hiding.

The growing caterpillars molt their skins several times to allow more room.  The stages between molts are called "instars;" butterfly and moth caterpillars have four or five instars.

My traveling caterpillar moved by using the six wiry thoracic legs up front (which will remain legs through adulthood) and ten "protolegs" in the back (which will be absorbed during metamorphosis).

Sooner or later, my caterpillar will pupate.  If it is a butterfly caterpillar, it will produce a smooth, molded chrysalis for the pupa stage.  More likely, this very fuzzy caterpillar is a moth and will spin a capsule of silk.

While often called the "resting stage," the pupa hardly seems restful.  The animal doesn't move around, but a lot goes on inside.

During metamorphosis, ten pairs of larval-cell bundles (called "imaginal discs") are activated by hormones to grow into adult features, such as wings and compound eyes.  In balance, certain larval structures degenerate; the full-rounded abdomen shrinks and most of the bristles reduce, for example.  (Metamorphosis from tadpole to frog involves more actual relocation of tissue.)

While our group was entertained by the caterpillar inching along the shore pine twig for some time, most people seem much more interested in the adult insect than in the larvae.  For insects with complete metamorphosis, however, the adult is usually just a fancy device for gene mixing and gene dispersal.  Most such insects spend more of their lives as fascinating caterpillars than as flamboyant adults.

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Wavecrest Discoveries can craft your personal discovery of this delightful part of our world by customizing one of our distinctive guided excursions.   Our walks, tours, and special activities are wonderful ways to explore this fascinating region—and are the perfect entertainment for guests.