What do butterflies, moths and skippers look like?

Butterflies, moths and skippers all belong to the Order Lepidoptera.

Size:

Body:

Long or stout.
Generally widest at wing attachment (wide shoulders), with abdomen tapered or column-like.
Body covered with scales and often hairy.
Appears soft or fragile.

Antennae:

Short to very long with many segments.
Butterflies and some day flying moths have club-like antennae with swollen tips.
Form for most moths highly variable.

Eyes:

Large, well separated and sometimes hairy.
Rarely reduced, ocelli (tiny single lens eyes) when present small, next to top of eye rather than top of head.

Mouthparts:

Wings:

Two pairs if present.
Both pairs membranous - often patterned or textured and cloudy.
Have few cross-veins forming at most long rectangular or triangular cells.
Hindwing generally wider and rounder than the more elongate and angular forewing.
Wings have overlapping scales though in some species it is restricted to the veins.
At rest, wings are held in a variety of ways. These include upright and pressed together above the body (butterfly, some moths), upright but not pressed together (some skipper butterflies), tent-like above body (moths) or horizontally spread so the hindwing and often the abdomen are visible (moths, some skippers, sun-basking butterflies).

Limbs:

Abdomen tip:

They are solitary or form large groups for mating, migration or roosting.
When disturbed they fly away or drop to the ground. During the day, roosting moths may undertake short flights to escape potential predators.
Most are strong fliers. Depending on the species they maybe capable of rapid flight, a loping flight or simply drift on air currents like a bird. Others have weak fluttering, often erratic flight.
Adults feed on nectar from flowers though some do not feed, and rely on the stored reserves accumulated from their larval stages.
Many are associated with particular plants, where they mate and lay eggs.
Some are sound producers although most emit ultrasonic sounds.
Many butterflies and moths (in particular) are experts of camouflage and deception. Many use colourations and patterning to blend in with their surroundings, or to deter predators.
They are active during the day (all butterflies and few moths) night (moths) or twilight periods; many are attracted to light.

Atypical moths are present throughout the Order Lepidoptera. Moths with reduced wings, or absent wings are found in several families. The case moths (Family Psychidae), looper moths (Family Geometridae), tiger moths (Family Arctiidae) and tussock moths (Family Lymantriidae) all have some species in which the female is flightless, having reduced or absent wings. They are still distinguished as moths as they have overlapping scales on their body.
Reduction and absence of the proboscis (haustellum) is also common across many families, and some families are comprised totally of species that do not feed as adults. This may sometimes cause confusion with other insects, but the presence of scales and two pairs of wings are usually sufficient to identify the insect as either a moth or butterfly.

Some moth species may look like wasps. Some species of case moths (Family Psychidae), cup moths (Family Limacodidae), clearwing moths (Family Sesiidae), forester moths (Family Zygaenidae), and hawk moths (Family Sphingidae) have clear wings, with scaling restricted to veins and the body of the moth. This can sometimes give a wasp-like appearance (eg. Family Sesiidae), and may result in incorrect identifications. The scales on the body should still identify these insects as moths.
Caddisflies may look remarkably like moths. They can be distinguished from moths by the combination of a lack of scales on the body, antennae longer than the body and their hair covered wings.