Butterflies, skippers, and moths are all members of the order Lepidoptera. Among them, moths have by far the largest numbers. There are five families of butterflies worldwide, one family of the closely related skippers, and 125 families of moths.
Many people wonder how to tell the difference between butterflies and moths. Some people think they know, but it is not so simple. It is commonly believed that moths are dull colored or white, while butterflies are brighter. This is true to a degree, but there are plenty of bright moths, such as the Uraniid moth, Chrysiridia madagascarensis, which has intense iridescent colors, and is one of the most vivid of the Lepidopterae. A number of butterflies, on the other hand, resemble dried leaves or dust.
Another determinant is thought to be the way the wings are held when the butterfly or moth lands. Moths hold their wings flat when at rest, while butterflies hold theirs together above their bodies. Again, this is generally true, but not completely reliable. Geometrid moths rest with their wings up, like butterflies, while Riodininae and Pyrginae butterflies hold their wings flat as if they were moths.
Moth larvae, in general, spin cocoons when they go through metamorphosis, as the silkworm caterpillars do, for example. Butterflies usually pupate, that is, undergo the stage between larva and adult, naked. But again, not always. Moths do have feathery or thread-like antennae, and butterflies have a club, a ball or hook, on the end of theirs. But not always. It is true though, that butterfly antennae are never feathery.
Possibly the most reliable way to tell them apart is the presence or absence of a frenulum or a jugum. Moths have a mechanism that hooks their double wings together in flight. Most have a frenulum, a strong bristle or group of bristles on the front base of the hind wing that catches on a special mass of scales or hairs on the corresponding front wing. It works something like Velcro, to hold the two wings as a single structure in flight. A smaller group of moths have a different structure, the jugum, which is a sort of lobe on the front wing that slips over the edge of the back wing.
Butterflies, as a rule, lack either structure. Their double wings are held together in flight by a broad overlap at their base. This would be a universal way to tell them apart, except that an Australian skipper, the Regent Skipper, Euschemon rafflesia, has a frenulum. And, as it happens, quite a few moths lack one.
Many believe that moths fly by night and butterflies by day, and this is almost true. Butterflies in general do only fly in the daytime or at dusk, but there are numbers of diurnal moths, ones that fly by daylight.
Skippers are nearly butterflies. Except to experts, they resemble them quite closely. The caterpillars pupate in a sort of cocoon that resembles a thin net strung from a few silk strands. Their colors are dim and dull, mostly, and they are small and quick, except for a few very large species.
Butterflies and moths appeal to almost all humans, as an embodiment of freedom and transcendence. The novelist Vladimir Nabokov apparently produced his great works mostly to raise money for butterfly-hunting expeditions. To many of us, their winged form is the most beautiful and ethereal we can imagine. After all, around the world, it is the fairies and the angels we have given wings.