Sooner or later, every lepidopterist gets asked the inevitable question by a friend. What’s the difference between a butterfly and a moth?

The Aurelian’s response is always the same. How long have you got?

There’s a reasonable argument that there is no difference. Of the one hundred and twenty seven different families of Lepidoptera, worldwide there are just five families that we loosely label “butterflies” because they seem to share certain characteristics – they’re colourful, day-flying, have clubbed antennae, and fold their wings vertically over a thinner body. These five families are the Papilionidae (Swallowtails), the Pieridae (Whites), the Nymphalidae (Brush-foots), the Lycaenidae (Blues, Coppers and Hairstreaks)* and the Hesperiidae (Skippers). All the rest, we dismiss as “moths”.

*(The Riodinidae (Metalmarks), previously tucked amongst the Lycaenidae, have recently earned themselves the status of a separate family. Their late entry possibly has something to do with the fact that only one species, Hamearis lucina, is found in Europe.)

Duke of Burgundy, Hamearis lucina – a Metalmark

Of these five main families, the first four are known as the “True Butterflies”, while the Skippers managed to sneak into this exclusive club in spite of being on the whole dull, boring, brown and a little bit mothy. They did this pretty much on the basis of a claim to be out and about during the daytime, and that butterfly books would be unprofitably thin without them. 

Sciron Ochre Skipper, Trapezites sciron – it’s a butterfly!

If you’re a Mediterranean cruise aficionado, you’ve probably been persuaded to take a trip to see the famous Butterfly Valley, on the Greek island of Rhodes. If so, you’ve been robbed – ask for your money back. This valley is plagued with an infestation of Euplagia quadripunctaria, aka the Jersey Tiger moth, which the Greek Tourism Board has in its unscientific wisdom elevated to the status of butterfly. Clearly Moth Valley just didn’t hit it with the tourists in quite the same way.

The Jersey Tiger – it’s a moth.

Australians, in their typically antipodean way, reverse the process with the insect they universally refer to as the Cabbage Moth – in this case a perfectly respectable butterfly that entomologists call  Pieris rapae, known throughout most of the English-speaking world as the Small White, or possibly the Cabbage White. It would seem to have nothing in its ancestry to suggest it deserves the term moth, other than perhaps as a term of disparagement for this pest of market gardens.

Small White, Pieris rapae – sorry Australia, it’s definitely a butterfly

However, there are a number of moths that would seem to have a strong a case to join this exclusive club, but have failed to get past the door – again probably as a result of not being European, and thus ignored by early lepidopterists.

We have the Castniidae, or the Sun Moths, that do a pretty convincing imitation of a small Meadow Brown or Gatekeeper on the wing. With their clubbed antennae and day-flying habits, they have in the past been considered butterflies by some authorities, and even included in some butterfly field guides, but have since been effectively relegated.  

A Sun Moth, clubbed antennae and all…

Then there are the so-called Swallowtail Moths, the Uraniidae. The Aurelian thoroughly thumbed through Braby’s “Butterflies of Australia” looking for Alcides metaurus on his first visit to Queensland, all in vain. This strong day-flying species gives a very convincing imitation of a large Swallowtail on the wing, but has so far failed to convince the taxonomists.

Alcides metaurus, the Zodiac Moth

Another group somewhat unfairly snubbed are the Zygaenidae. As a colourful, day-flying family with significant European membership, they would seem to have had a reasonable case to be elevated to the status of butterflies.

A striking member of the Zygaenidae family, the Burnet moths

It’s not unknown for some species of this family to even go to the extent of disguising themselves as other butterflies in an attempt to join the party. 

Another Zygaenidae moth, disguising itself as..
…a Swallowtail butterfly.

And then we have the ultimate try-hards, the Butterfly Moths. Not to be confused with the Moth Butterfly, Liphyra brassolis a crepuscular Asian and Australian butterfly species that somehow manages to get itself included amongst the Lycaenidae, whilst having no apparent resemblance to any other species within the family. No, the Butterfly Moths, sometimes also known as the Moth Butterflies (yes, it is confusing) are a series of American species belonging to the family Hedylidae, which muscled themselves into the butterfly club, were subsequently rejected, and then reinstated recently on appeal.

Hedylidae

So, what is the difference between butterflies and moths? Is it the possession of certain physical characteristics? Is it membership of the five (or is it six, or is it seven) exclusive families? Taxonomists will tell us that butterflies evolved from moths around 100 million years ago, not the other way round, so perhaps it’s simpler if we abandon all discrimination, and just refer to certain insects as day-flying moths?

Just a day-flying moth?

Now next time you’re asked, you can confidently echo The Aurelian’s response.

How long have you got?