Sunday, 18 August 2013

The difference between butterflies and moths

Here is a moth pretending to be a butterfly, which prompts me to ponder the difference between the two. It is a question often raised by visitors, especially children, and it is a good one because the two types of insect belong to the same order, Lepidoptera or scaled-wings, and even eminent scientific classifiers have had problems in deciding whether particular, debatable, species are butterflies or moths.

But there are handy rules for the amateur and if there are exceptions to all of them, that merely proves them. The simplest is that all butterflies fly by day and most moths at night. There are certainly fewer human observers around at night, of course, should a butterfly venture forth, but neither I nor anyone I know has ever had one come to the trap.

Plenty of moths fly by day, however, and many of them are gaily-coloured which makes a second common rule, that butterflies are brightly and moths dull, too dodgy to accept, so I have shaded it grey. Having said that, I think it is quite useful for beginners as a general rule of thumb and it relates to the next one: butterflies and moths operate their wings differently.

That brings in my picture, because almost all butterflies rest with their wings raised above their bodies like the moth in my photograph (hence the title of the post). Moths almost always fold their wings flat and back like a diver or jetplane as you can see at your leisure via most pictures on this blog's past posts. This is in part due to the frenulum which connects fore- and hindwings, which moths have and butterflies don't. It accounts for the high-speed, whirring, dippy-dodging flight of moths compared with the airy floating of butterflies (albeit a floating which can put on an impressive turn of speed, as birds and entomological photographers know).

Read this and think of butterflies
Last but most useful in diagnosis: almost all butterflies have simple antennae like the gearstick of a Morris Minor or a club, while moths' resemble every form of TV aerial known to man.  I shall leave it there, but please add any words of wisdom in Comments to help my explanations to novices (of whom we have more coming to tea today). Pupae for example: butterflies always develop in a hard-skinned chrysalis, never a cocoon, while many moths weave the latter.  But that and caterpillars (moths win hands-down for colour, bristles and general jaw-dropping variety) are unrelated to observations of the adult insects. On which note, here are a few of last night's moths:

The rakish Angle Shades, one of the most jetplaney of moths

An Orange Swift, casting doubt on nomenclature. This is a female; in a mothy
tweak on Adam and Eve, it's the male that gets the orange

I think that this is a Yellow-barred Brindle, though why it gets that name eludes
me; maybe because its green gradually fades to yellow

And here's another one, illustrating the differences within a species. The weird
thing top right is the leg of an eggbox's cartoon Happy Hen

Another exception to the rules: delicate Laura Ashley moths such as this
Common Wave often rest with their wings spread wide, a habit shared with
butterflies. But they never hold them up, like the moth in my first pic today


Purple Centipede said...

I've had Butterflies come to my trap on 3 occasions, (Speckled Wood, Peacock & Comma), all on rainy nights though)

Martin Wainwright said...

Hi Purple Centipede - great name

That's very interesting to hear. It would be fascinating to track them and see how they got there. I must look for other similar records online. Thanks ever so for taking the trouble to let me know

All warm wishes