Interesting facts about caterpillars
SURELY you’ve seen a caterpillar in your lifetime and you’ve probably even handled one, but how much do you know about lepidopteran larvae? These cool facts about caterpillars will give you new respect for what remarkable creatures they are.
A caterpillar has just one job—to eat: During the larval stage, the caterpillar must consume enough to sustain itself through its pupal stage and into adulthood. Without proper nutrition, it may not have the energy to complete its metamorphosis. Caterpillars can eat an enormous amount during a lifecycle stage that typically lasts several weeks. Some consume 27 000 times their body weight during their lifetime.
Caterpillars increase their body mass by as much as 1 000 times or more: The larval stage of the lifecycle is all about growth. Within the span of a few weeks, the caterpillar will grow exponentially. Because its cuticle or skin is only so pliable, the caterpillar will molt multiple times as it gains size and mass. The stage between molts is called an instar, and most caterpillars go through five to six instars before pupating.
A caterpillar's first meal is usually its eggshell: In most cases, when a caterpillar hatches from its egg, it will consume the remainder of the shell. A caterpillar has as many as 4 000 muscles in its body: That’s one seriously muscle-bound insect. The caterpillar’s head capsule alone consists of 248 individual muscles. About 70 muscles control each body segment. Remarkably, each of the 4 000 muscles is innervated by one or two neurons.
Caterpillars have 12 eyes: On each side of its head, a caterpillar has six tiny eyelets called stemmata, arranged in a semi-circle. One of the six eyelets is usually offset a bit and located closer to the antennae. If you watch a caterpillar, you’ll notice it sometimes moves its head from side to side. This most likely helps it judge depth and distance as it navigates somewhat blindly.
Caterpillars produce silk: Using modified salivary glands along the sides of their mouth, caterpillars can produce silk as needed. Some caterpillars like gypsy moths disperse by “ballooning” from the treetops on a silken thread. Bagworms use silk to join dead foliage together into a shelter. Caterpillars also use silk when they pupate, either to suspend a chrysalis or construct a cocoon.
Caterpillars have six legs, just as adult butterflies or moths do: There are way more than six legs on most caterpillars you’ve seen, but most of those legs are false legs called prolegs, which help the caterpillar hold onto plant surfaces and allow it to climb. The three pairs of legs on the caterpillar’s thoracic segments are the true legs, which it will retain into adulthood.
Caterpillars move in a wavelike motion, from back to front: Caterpillars with a full complement of prolegs move in a fairly predictable motion. Usually, the caterpillar will first anchor itself using the terminal pair of prolegs and then reach forward with one pair of legs at a time, starting from the hind end. There's more going on than just leg action, though. The caterpillar’s blood pressure changes as it moves forward, and its gut, which is basically a cylinder suspended inside its body, advances in sync with the head and rear end.
Caterpillars get creative when it comes to self defence: Life at the bottom of the food chain can be tough, so caterpillars employ all kinds of strategies to avoid becoming a bird snack. Some caterpillars, such as the early instars of black swallowtails, look like bird droppings.
Other caterpillars use the opposite strategy, making themselves visible with bright colours to advertise their toxicity. A few caterpillars, like the spicebush swallowtail, display large eyespots to deter birds from eating them. A swallowtail caterpillar can be identified by its smelly osmeterium, a special defensive stink gland just behind the head.
Many caterpillars use the toxins from their host plants to their own advantage: Caterpillars and plants co-evolve. Some host plants produce toxic or foul-tasting compounds meant to dissuade herbivores from munching their foliage, but many caterpillars can sequester the toxins in their bodies, effectively using these compounds to protect themselves from predators.