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Differences between butterflies and moths

A common classification of the Lepidoptera involves their differentiation into butterflies and moths. Butterflies are a natural monophyletic group, often given the sub-order Rhopalocera, which includes Papilionoidea (true butterfiles), Hesperiidae (skippers), and Hedylidae (butterfly moths). In this taxonomic scheme moths belong to the sub-order Heterocera. Other taxonomic schemes have been proposed; the most common putting the butterflies into the sub-order Ditrysia and then the "super-family" Papilionoidea, and ignoring a classification for moths. None of the taxonomic schemes are perfect however, and taxonomists commonly argue over how to define the obvious differences between butterflies and moths.

'Butterfly' Families

The following families of Lepidoptera are usually considered as butterflies :-

Swallowtails and Birdwings, Papilionidae
Whites or Yellow-Whites, Pieridae
Blues and Coppers or Gossamer-Winged Butterflies, Lycaenidae
Metalmark butterflies, Riodinidae
Brush-footed butterflies, Nymphalidae which contain the following 13 subfamilies:

the snout butterflies or Libytheinae (formerly the family Libytheidae).
the Danaids or Danainae (formerly the family Danaidae).
the Tellervinae.
the glasswings or Ithomiinae.
the Calinaginae.
the morphos and owls or Morphinae (including the owls as tribe Brassolini).
the Browns or Satyrinae (formerly the family Satyridae).
the Charaxinae (preponas and leaf butterflies).
the Biblidinae.
the Apaturinae.
the nymphs or Nymphalinae.
the Limenitidinae (especially the adelphas) (formerly the family Limenitididae).
the tropical longwings or Heliconiinae.

The other families of the Lepidoptera are considered to be moths.

Morphological differences

Shape and structure of antennae

The most obvious difference is in the feelers, or antennae. Most butterflies have thin slender filamentous antennae which are club shaped at the end. Moths, on the other hand, often have comb-like or feathery antennae, or filamentous and unclubbed. This distinction is the basis for the earliest taxonomic divisions in the Lepidoptera - the Rhopalocera ("clubbed horn", the butterflies) and the Heterocera ("varied horn", the moths).

There are, however, exceptions to this rule and a few moths (the family Castniidae) have clubbed antennae. Some butterflies, like Pseudopontia paradoxa from the forests of central Africa, lack the club ends. The Hesperiids often have an angle to the tip of the antenna.

Wing coupling mechanisms

Many moths have a frenulum which is a filament arising from the hindwing and coupling with barbs on the forewing. The frenulum can be observed only when a specimen is in hand. Some moths have a lobe on the forewing called a jugum that helps in coupling with the hindwing. Butterflies however lack these structures.

Pupae

Most moth caterpillars spin a cocoon made of silk within which they metamorphose into the pupal stage. Most butterflies, on the other hand, form an exposed pupa, also termed a chrysalis.

There are many exceptions to this rule, however. For example, the Hawk moths form an exposed chrysalis which is underground. Gypsy moths sometimes form butterfly-style pupae, hanging on twigs or tree bark, although usually they create flimsy cocoons out of silk strands and a few leaves, partially exposing the chrysalis. A few Skipper butterfly larvae also make crude cocoons in which they pupate, exposing the pupa a bit. The Parnassius butterfly larvae make a flimsy cocoon for pupation and they pupate near the ground surface between debris.

Colouration of the wings

Most butterflies have bright colours on their wings. Nocturnal moths on the other hand are usually plain brown, grey, white or black and often with obscuring patterns of zigzags or swirls which help camouflage them as they rest during the day. However many day-flying moths are brightly-coloured, particularly if they are toxic. A few butterflies are also plain-colored, like the Cabbage White butterfly.

Structure of the body

Moths tend to have stout and hairy or furry-looking bodies, while butterflies have slender and smoother abdomens. Moths have larger scales on their wings which makes them look more dense and fluffy. Butterflies on the other hand possess fine scales. This difference is possibly due to the need for moths to conserve heat during the cooler nights whereas butterflies are able to absorb solar radiation.

Behavioural differences

Time of activity

Most moths are nocturnal or crepuscular while most butterflies are diurnal. There are however exceptions, including the diurnal Gypsy moth and the spectacular "Uraniidae" or Sunset moths.

Resting posture

Moths usually rest with their wings spread out to their sides. Butterflies frequently fold their wings above their backs when they are perched although they will occasionally "bask" with their wings spread for short periods. However some butterflies, like the skippers, may hold their wings either flat, or folded, or even in-between (the so-called "jet plane" position) when perched. Most moths also occasionally fold their wings above their backs when they are in a certain spot (like when there is no room to fully spread their wings). A sometimes confusing family can be the "Geometridae" (such as the Winter moth) because the adults often rest with their wings folded vertically. These moths have thin bodies and large wings like many butterflies but may be distinguished easily by structural differences in their antennae (e.g. bipectinate).