Difference between a butterfly and a moth

A common classification of the Lepidoptera involves their differentiation into 'butterflies' and 'moths'. This separation is not one that is recognized by taxonomists since the "moths" are an artificial group, defined only as everything in the order that is not a butterfly. Butterflies, on the other hand, are a natural group (they are all descended from a single common ancestor, so the group is monophyletic), and this group is often given the name Rhopalocera - however, this name does not have a formal taxonomic rank, and is only used in modern rankless classifications (e.g. The Tree of Life Project). The corresponding name Heterocera (for the moths) is completely obsolete, and only appears in older literature.

What is the difference between a butterfly and a moth?

Taxonomically, the folk category of butterfly may be considered as a combination of the lepidopteran superfamilies Papilionoidea and the Hesperioidea, while the remaining groups are usually termed as moths. Some of the smaller moths can, however, easily be mistaken for flies.

The differences within these two groups are on the basis of

morphology
- antennae
- wing coupling mechanisms
- pupae
- colouration
- structure of the body

and

behaviour
- resting posture
- time of activity (diurnal/nocturnal)

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 non-standard 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 clubbed 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 which is also termed as a chrysalis.

However there are many exceptions to this rule, for example the Hawk moths form an exposed chrysalis which however is underground. Gypsy moths form butterfly-style pupae, hanging on twigs or tree bark.

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 a stout and hairy or furry-looking bodies, while butterflies have slender and smoother abdomens. Moths have larger scales on their wings which make 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" 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).

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