Caterpillars are eating machines with a toolkit of disguises and chemical weapons
A tobacco hornworm can multiply its weight ten-thousandfold in under twenty days. Caterpillars exist to eat, and because so many animals want to eat them in turn, they have evolved an astonishing range of tricks, from posing as bird droppings to whistling at birds and hiring ants as bodyguards.
A caterpillar is the larval stage of a butterfly or moth. The English word, dating from the early sixteenth century, probably comes from an Old North French phrase meaning hairy cat. Most eat plants, but not all: around one per cent prey on insects, clothes moth larvae eat wool, and one Hawaiian species traps snails with silk. Sizes run from a millimetre to 14 centimetres. They usually moult four or five times before pupating, and a specialised gut that pumps potassium ions helps them process vast quantities of leaves.
Camouflage is the first line of defence. One North American species even changes appearance with the seasons: larvae hatching in spring and feeding on oak catkins turn green, while summer hatchlings eat tannin-rich leaves and grow up resembling twigs. Others mimic thorns or droppings, and bagworms build portable cases of sand and plant debris. Inchworms, whose family name means earth-measurer, loop along because they have lost nearly all their hind prolegs.
Other species fight back. Some carry irritating or venomous hairs; others store toxins from their food plants and advertise with bold red, yellow and black stripes, as monarch and cinnabar moth larvae do, keeping those chemicals into adulthood. Swallowtail larvae push out foul-smelling glands, hornworms flick whip-like tails at wasps, and the walnut sphinx caterpillar whistles. Some lycaenid caterpillars pay ants in sugary food in return for protection, while pine processionary caterpillars travel nose to tail in long lines.
Caterpillars can devastate crops, especially in monocultures, and many have evolved resistance to both pesticides and the bacterial toxin Bt engineered into some plants. Fossils show they are ancient: a geometrid caterpillar about 44 million years old was found in Baltic amber in 2019, and an even older one, around 125 million years, in Lebanese amber. Silk, meanwhile, comes entirely from one domesticated caterpillar.
Source: Caterpillar
