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 clubbed ends. The "Hesperiids" often have an angle to the tip of the antenna.
Many moths have a "frenulum" or wing coupling physically attaching upper and lower parts of their wings together. The frenulum can be seen only when a specimen is in hand. There are various types. It may be a filament from the hindwing coupling with barbs on the forewing. Butterflies usually lack these structures. Their wing coupling is usually done by simple overlap of wing edges.
Most moth caterpillars spin a cocoon made of silk when they go into the pupal stage. Most butterflies on the other hand form an exposed pupa called a chrysalis.
There are many exceptions to this rule. 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.
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 quite plain, like the cabbage white butterfly.
Moths tend to have stout and hairy or furry-looking bodies. Butterflies on the other hand have slender and smoother abdomens. Moths have larger scales on their wings. These make them look more dense and fluffy. Butterflies on the other hand have 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 sunlight.
Most moths are nocturnal or crepuscular (active at night) while most butterflies are diurnal (active at daytime). There are however exceptions, including the diurnal gypsy moth and the spectacular "Uraniidae" or Sunset moths.
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).
Monophyly
Monophyly means common descent from a single ancestor.
Biologists have introduced a kind of taxonomy called cladistics. The aim of this is to make biological classification fit what we know about the way organisms evolved.
If there is a group made of a common ancestor, and all its descendants, that group is monophyletic. (Greek: "of one race").
A group which contains organisms, without their common ancestor, is called polyphyletic. Convergent evolution is a usual cause of such groups. If a group contains the common ancestor, but leaves out some of its descendants, it is called paraphyletic. All living things on this planet are thought, on the basis of DNA analysis, to be monophyletic, that is, to have one origin, not many.
Example: all species in the genus "Homo" have come from the same ancestral form in the family Hominidae, and no other descendants are known. Thus the genus "Homo" is monophyletic.
If, on the other hand, it were discovered that "Homo habilis" had developed from a different ancestor from "Homo sapiens", and this ancestor were not included in the genus, then the genus would be polyphyletic. Since biologists by and large tend to prefer monophyletic groups, in this case, they would likely either split the genus or broaden it to include the additional forms.
Example of polyphyletic group: Sea slugs.
Sometimes taxonomists are frustrated fitting plant species into a monophyletic group because of polyploidy. There is clear evidence that some polyploid plant species are of multiple origins (the species has arisen more than once). For example, "Salsify", the hybrid goat's-beard, ("Tragopogon miscellus") has formed as many as 20 times in eastern Washington.
Also, it can happen that hybrids between two close plant species undergo polyploidy, and the polyploids continue as a new and distinct species. Situations like this are outside the normal rules of descent, and are dealt with by special decisions, guided by the International Commission of Botanical Nomenclature (ICBN).
Lepidoptera
The order Lepidoptera is the second biggest order of insects. It includes the moths and butterflies including the skippers. There is no common word for the group: ordinary people talk of "butterflies and moths".
The order has more than 180,000 species in 128 families and 47 superfamilies. They are 10% of all the described species of living organisms. The Coleoptera (the beetles) is the only order that has more species.
The name, Lepidoptera, comes from the Ancient Greek words "λεπίδος" (scale) and "πτερόν" (wing).
The earliest discovered fossils date to 200 mya or earlier. This early origin was long before flowering plants evolved. Earlier butterflies must have been adapted to a habitat of cycads and conifers, something which had not previously been suspected.
Lepidopterans go through complete metamorphosis. This means that they have a four parts to their lives. The first part is the egg. The second part is the caterpillar or larva. The third part is the pupa. The last part is the adult or imago.
The larvae have a tough head and a soft body. They have mouths that are made to chew. Some larvae are covered with hairs, or other body extensions. The larvae have three pairs of small legs on the thorax. These legs are called true legs. There are up to five pairs of bigger legs on the abdomen. These legs are called prolegs. Lepidopteran larvae can be confused with the larvae of sawflies. The difference between Lepidopteran larvae and sawfly larvae is that Lepidopteran larvae have tiny hooks on their prolegs. These hooks are called crochets. Most larvae are herbivores, but a few are carnivores and detritivores.
Adults have two pairs of wings. They are covered by small scales. In some species, the adults have very small wings or no wings at all. This is more common in females. Adults have antennae. Some moths have antennae that look like feathers. These feather-like antennae are larger in males than females. Adults have a mouthpart called a proboscis. It sucks nectar from flowers. Some adults do not have mouths and cannot feed. Others have different mouths that are made to pierce and suck blood or fruit juices.
Diurnal
Animals that are active during the day are called diurnal. They hunt or feed during the day and sleep during the night. Nocturnal animals do it the other way round.