The Secret Life of Caterpillars

Adaptive caterpillars play a key part in forest, fields, and ecosystems everywhere.

Cecropia Moth Larva

Head on, the body of a four-inch long cecropia moth larva looks like an ornate pin cushion; a colorful, yet formidable obstacle for hungry birds.

Photo by Gerry Lemmo

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One foot in front of the other – and a lot of feet at that. Plodding along, the caterpillar’s means of locomotion depends upon its several pairs of legs. Equipped with tiny claws designed for superior traction on surfaces ranging from smooth new leaves to rough tree bark and narrow pine needles, these versatile animals really get around. With as many as 4,000 muscles throughout a caterpillar’s body, compared to only 629 in the human body, it’s quite understandable that these small creatures are not only extremely flexible, but capable of gripping firmly onto severely windswept tree boughs, like high-wire performers in a circus act.

The immature or larval stage of either a butterfly or moth (these are combined into the scientific order known as Lepidopterans), a caterpillar is a remarkably well-adapted piece of biological engineering. Although most start out with more legs than a small dance company, only their six true legs, a trait of all insects, remain with them when they transform into adults, through the miracle of metamorphosis.

Because of their laid back lifestyles, caterpillars frequently attempt to blend into their surroundings. Often resembling brown twigs or green stems to which they cling, many have evolved with plantlike growths on their bodies. Some have gone so far as to develop weird shapes that appear as partially eaten leaves, accented by strange patterns of leaf decay stenciled along their lengths.

However, as a whole, our North American species display every color of the rainbow, ranging from lemon yellow to powder blue, and even shocking pink in one southern variety. Many sport racing stripes, bands, dots and bizarre hairstyles, and with these outlandish designs, loudly proclaim their distastefulness to birds and other predators. Those with the most vibrant colors and showy markings, such as the brightly banded larva of our revered monarch butterfly, are likely recognized by many birds as being toxic.

With irritating hairs or spines that can cause mild to severe allergic reactions in human skin, some species of North American caterpillars are best left untouched. One group of moth caterpillars, endemic to the Amazonian region of South America, is so toxic that a number of human deaths have actually been attributed to direct contact with them.

Born Mimics

Some Lepidopteran larvae have even evolved to mimic other animals, like snakes or wide-eyed mammals, intimidating their aggressors with artificial eyes that stare back at them. The larvae of both the tiger and spicebush swallowtails are good examples of this phenomenon. In its last instar, or growth stage, before changing to a chrysalis, the mature spicebush caterpillar turns yellow or orange and, viewed from head on, resembles a jack-o’-lantern, with its oversized, glaring “pupils” impossible to miss. Below a black lip marking is the true head of the insect, curled out of sight. As a backup strategy to avoid being eaten, all swallowtail larvae also produce, on demand, an inflatable, forked organ when disturbed. This brightly colored gland, called the osmeterium, mimics a snake’s tongue, and, when extended, gives off a foul odor to boot. A gently handled specimen, though harmless to humans, will very likely put on a show.

While it might be easy to overlook the presence of caterpillars within any terrestrial environment, the fact they exist is the foundation for other life forms that depend upon these larvae for survival. Since their numbers and varieties are immense, many species are a prime food source for other creatures, right on up to the top of the food chain. If it was not for the abundance of these protein-packed land lubbers, our forests would be silent, mainly due to the lack of birds, for many of which survival is dependent on insects.

The arrival of migratory songbirds in spring is timed, greatly, by the presence of newly hatched caterpillars, for as soon as the budding leaves of trees emerge, one can expect to see armies of small avian predators seeking and destroying the larvae in untold quantities. The birds will develop a still greater dependency on this nearly limitless food source once their young have hatched. Soft-bodied caterpillars tend to be an easy-to-digest item for baby birds, thereby placing them among the favorites on nature’s menu.

Chow Down

As a constant force of defoliation, hordes of Lepidopteran larvae can sometimes wreak havoc on acres and acres of both wild and cultivated growth. On the flip side, they also produce huge amounts of organic waste as a by-product of their incessant feeding.

Caterpillars are incredible eating machines, gaining thousands of times their weight from the time they hatch from a tiny egg to the final growth stage before they form a chrysalis or a cocoon – a period of time that typically averages about two weeks.

Under a thick canopy of forest leaves, where an abundance of feeding caterpillars may exist, their droppings, known as frass, can sound like rainfall on the sunniest of days. With that much activity in a healthy ecosystem, the forest floor is carpeted by that all-important organic waste, helping replenish nutrients the host plants take from the soil.

As with everything unaltered in nature, there is a rule of give and take that tends to keep a delicate balance of life.

Whether in the forest or in the garden, spared of toxic chemicals, a multitude and diversity of cater-pillars is sure to be encountered. While they may be categorized as being either beneficial or harmful – depending upon varying human standards – be assured they have their well-earned place in their natural, native environments.

Caterpillars most certainly demand recognition in more than one way; certainly for their great value within the web of life. And then, of course, standing on their own visual merits, as the unique and frequently beautiful creatures they are, with their magical ability to bring awe, amusement and sheer delight to children and adults of all ages.

Learn how to attract butterflies to your home by reading Privacy Hedges Attract Butterflies.


Gerry Lemmo, who lives in upstate New York, is a professional photographer, naturalist, and lecturer specializing in wildlife, natural history and travel images from around the globe.