What is the difference between butterflies and moths?

It probably won’t surprise you to learn that moths and butterflies are very similar. Just by looking at them, we know that there must be a relationship between the two types of insects. And they actually belong to the same group of flying insects, called Lepidoptera, which comes from the Greek for “scale wings”.

Both butterflies and moths share similar life cycles and look so similar that it can be difficult to tell them apart. There are somewhat monochromatic butterflies that look like moths, and colourful moths that look like butterflies.

However, if you look carefully (and know what to look for) you can quickly find some differences between butterflies and moths. Read on to learn more about both groups of insects, so you can identify and distinguish them like a pro.

How are butterflies and moths alike?

Before we discuss the difference between butterflies and moths, it may be useful to focus on what makes them so similar. We have already told you that they are lepidopteran insects and that they are closely related.

Both moths and butterflies share wings covered with microscopic scales. However, at least from an evolutionary point of view, it is likely that the two species did not arise at the same time.

Butterflies are thought to have evolved from moths, existing as the daytime equivalent of moths. The colourful butterflies we now know evolved much later, after the emergence of flowering plants some 150 million years ago.

As adult, flying insects, moths, and butterflies are in the final act of a four-stage life cycle shared by Lepidoptera.

This cycle begins with the egg, passes through the caterpillar (larva) and chrysalis (pupa) stages, and finally ends with the adult stage, usually called the imago. This imago can be a butterfly or a moth. And in this metamorphosis we find the first difference.

Differences between butterfly and moth pupae

Most moth caterpillars weave a silk cocoon into which they metamorphose in the pupa stage. You probably already know that silk threads are obtained from the pupae of the Bombyx mori moth, a fully domesticated species that cannot live without human care.

Instead, most butterfly caterpillars form a pupa made of a hardened protein, also called a chrysalis. These butterfly chrysalises can be gorgeous, with intricate and colourful patterns and textures.

There are, however, some exceptions to the rule. Some moths do not form pupae, and simply remain buried, though exposed, during metamorphosis. A few butterflies also do not form elaborate chrysalises, leaving the pupa partially exposed.

Different as night and day  

In French, butterflies and moths have interesting names. They are called, respectively, “papillons de jour” (day butterflies) and “papillons de nuit” (night butterflies). But is this useful as a criterion for distinguishing them?

It certainly is. Most moths are nocturnal or crepuscular, while most butterflies are diurnal. There are species of moths that fly both day and night, although they are a rare exception to the rule.

Moths often use moonlight to navigate, which is why they are often confused by artificial lights in our homes. It is believed that they are not attracted to light, only confused by it.

Although the mass lighting of our cities is a relatively recent event, we are already having an impact on their habits. A group of researchers determined in 2016 that city moths are evolving to be less attracted to artificial lights.

Colour, or lack thereof, can distinguish them

The habits of moths and butterflies have an impact on their appearance. For how important can the brightest colours be in the almost total darkness of night?

Nocturnal moths are usually brown, grey, white, or black. This austerity in colour is accompanied by patterns that help them camouflage themselves from predators when they rest during the day.

In contrast, most butterflies have brightly coloured wings. The few species of diurnal moths are also often brightly coloured, especially if they are toxic (as a warning sign).

Colour is also used to find a mate. Diurnal species of Lepidoptera evolved to locate mates visually, unlike nocturnal species that use pheromones. These are highly volatile chemicals that are dispersed through the air.

The structure of their bodies may be the key to distinguishing them

Moths tend to have a stout, hairy body. Butterflies, on the other hand, have a thinner, softer abdomen. Moths also have larger wing scales, which make them appear denser and fluffier.

The scales on butterfly wings are very fine. Some are so fine that they scatter light in whimsical ways, forming a very attractive iridescent effect.

This difference in their bodies and wings is probably due to the moths’ need to conserve heat during the coldest nights. Butterflies have no such problem, being able to absorb sunlight.

But perhaps the most noticeable difference between butterflies and moths is in their antennae. Most butterflies have thin, rod-shaped antennae at the end. Moths, on the other hand, tend to have larger, branched, feather-like antennae.

Moths and butterflies smell (or, rather, detect chemicals in the air) through their antennae, and the need for this sense is greater in moths. This is because moths must rely more on their sense of smell, as low night-time lighting limits their vision.

Maybe they just need to be seen resting

If you see them resting, you may not need anything else to distinguish between butterflies and moths. Moths usually rest with their wings spread out to the side, attached to or very close to the surface on which they perch.

When perched on a surface, butterflies usually fold their wings together above the body, although they occasionally bask in the sun with their wings outstretched for brief periods. Many moths may also fold their wings together when there is no space to hold them outstretched.

In the end, it seems that there are no hard and fast rules for distinguishing butterflies and moths, but surely, you now have additional information about the differences between the two groups of lepidopteran insects. Thank you for joining us at the end of this exciting journey.

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