Butterflies | Can’t Sleep? Learn About Metamorphosis

Benjamin Boster (0:02)

Welcome to the I Can't Sleep Podcast, where I help you drift off one fact at a time. I'm your host, Benjamin Boster, and tonight's episode is about butterflies.

Butterflies are winged insects from the Lepidopteran superfamily Papillanoidea, characterized by large, often brightly colored wings, that often fold together when at rest, and at conspicuous fluttering flight. The oldest butterfly fossils have been dated to the Paleocene, about 56 million years ago, though molecular evidence suggests that they likely originated in the Cretaceous. As holometabolous insects, butterflies undergo complete metamorphosis, meaning that their life cycle comprises four stages. Winged adults lay eggs on plant foliage, on which their larvae, known as caterpillars, will feed. The caterpillars grow, sometimes very rapidly, and when fully developed, pupate in chrysalis. When metamorphosis is complete, the pupal skin splits, the adult insect climbs out, expands its wings to dry, and flies off.

Some butterflies, especially in the tropics, have several generations in a year, while others have a single generation. And a few in cold locations may take several years to pass through their entire life cycle.

Butterflies are often polymorphic, and many species make use of camouflage, mimicry, and anaposematism to evade their predators. Phaism is when a butterfly doesn't fully undergo melanism. Some, like the monarch and the painted lady, migrate over long distances. Some species are pests because in their larval stages, they can damage domestic crops or trees. Other species are agents of pollination of some plants. Larvae of a few butterflies, e.g. harvesters, eat harmful insects, and a few are predators of ants, while others live as mutualists in association with ants. Culturally, butterflies are a popular motif in the visual and literary arts. The Smithsonian Institution says butterflies are certainly among the most appealing creatures in nature.

The Oxford English Dictionary derives the word straightforwardly from Old English, Butterfly. Similar names in Old Dutch and Old High German show that the name is ancient, but modern Dutch and German use different words, Flinder and Schmetterling. And the common name often varies substantially between otherwise closely related languages. A possible source of the name is the bright yellow male of the brimstone. Another is that butterflies were on the wing and meadows during the spring and summer butter season, while the grass was growing.

Butterfly adults are characterized by their four scale-covered wings, which give the Lepidoptera their name. Ancient Greek, Lepis, Scale, plus Teron, Wing. These scales give butterfly wings their color. They are pigmented with melanins that give them blacks and browns, as well as uric acid derivatives and flavons that give them yellows. But many of the blues, greens, reds, and iridescent colors are created by structural coloration, produced by the microstructures of the scales and hairs.

As in all insects, the body is divided into three sections, the head, thorax, and abdomen. The thorax is composed of three segments. Each was a pair of legs. In most families of butterfly, the antennae are clubbed, unlike those of moths, which may be thread-like or feathery. The long plebiscis can be coiled when not in use for sipping nectar from flowers.

Nearly all butterflies are diurnal, have relatively bright colors, and hold their wings vertically above their bodies when at rest. These features differentiate butterflies from the majority of moths, which fly by night, or often cryptically colored, well camouflaged, and either hold their wings flat touching the surface on which the moth is standing, or fold them closely over their bodies. Some day-flying moths, such as the hummingbird hawk moth, are exceptions to these rules.

Butterfly larvae, caterpillars, have a hard head with strong mandibles, used for cutting their food, most often leaves. They have cylindrical bodies, with ten segments to the abdomen, generally with short prolegs, on segments three through six and ten. The three pairs of true legs on the thorax have five segments each. Many are well camouflaged. Others are aposematic, with bright colors, and bristly projections containing toxic chemicals obtained from their food plants. The pupa or chrysalis, unlike that of moths, is not wrapped in a cocoon.

Butterflies are distributed worldwide, except Antarctica, totaling some 18,500 species. The monarch butterfly is native to the Americas, but in the 19th century or before spread across the world, and is now found in Australia, New Zealand, other parts of Oceania, and the Iberian Peninsula. It is not clear how it disbursed. Adults may have been blown by the wind, or larvae or pupae may have been accidentally transported by humans. But the presence of suitable host plants in their new environment was a necessity for their successful establishment.

Many butterflies, such as the Painted Lady, Monarch, and several Danaen, migrate for long distances. These migrations take place over a number of generations, and no single individual completes the whole trip. The eastern North American population of Monarchs travels thousands of miles southwest to overwintering sites in Mexico. There is a reverse migration in the spring. It has recently been shown that the British Painted Lady undertakes a 9,000-mile round trip in a series of steps by up to six successive generations, from tropical Africa to the Arctic Circle, almost double the length of the famous migrations undertaken by monarch. Spectacular large-scale migrations associated with the monsoon are seen in Peninsular India. Migrations have been studied in more recent times using wing tags, and also using stable hydrogen isotopes. Butterflies navigate using a time-compensated sun compass. They can see polarized light, and therefore orient even in cloudy conditions. The polarized light near the ultraviolet spectrum appears to be particularly important. Many migratory butterflies live in semi-arid areas, where breeding seasons are short. The life histories of their host plants also influence butterfly behavior.