Butterflies and moths form the insect order Lepidoptera. The word ‘Lepidoptera’ comes from the Greek ‘lepis’ meaning scale and ‘petron’ meaning wing. When you look at the wing of a butterfly or moth under a microscope, you’ll see thousands of tiny scales.
New Zealand has over 1,800 species of Lepidoptera. Only 17 of these are butterfly species – that’s a tiny 1%! So how do you distinguish a butterfly from a moth?
Look at their antennae
In New Zealand, there is one feature that is infallible for distinguishing a butterfly from a moth. Just look at their antennae. If there are expanded knobs on the end of their antennae, the specimen you’re looking at is a butterfly.
In comparison, moth antennae are tapered to a point and often feathery.
Some behavioural or anatomical criteria
Other behavioural or anatomical criteria are useful in supporting the categorisation of a specimen as a butterfly or a moth, but they are not diagnostic by themselves.
Active during the day: Butterflies are mostly active during the day (diurnal), and moths are mostly active during the night (nocturnal). While this is usually true, there are moth species in New Zealand (like the magpie moth) that are also active during the day.
Resting position of wings: Butterflies rest with their wings closed together above the body, making only the undersides of the wings visible. Moths tend to rest with the wings spread flat or roof-like, so that only the upper surface is visible.
Wings in flight: In flight, butterfly wings simply overlap, so that the rear edge of the forewing pushes on the front edge of the hindwing during the downstroke. However, most moths have a coupling mechanism consisting of a bristle and catch device that couples the forewings and hindwings together.
Other feature differences between butterflies and moths
There are a few other features that people sometimes use to differentiate butterflies from moths. Although these features may be true for some butterflies, they do not occur in some of our native New Zealand species.
Colour: Butterflies are usually thought to be colourful. Many native butterflies like the tussocks or the coppers have colourful markings on the upper side of their wings. However, their undersides have duller colours and patterns, making them well camouflaged when their wings are closed.
Pupation: Butterfly pupae are thought to hang as unprotected chrysalises, while moths pupate underground, on the ground or protect their chrysalis with a woven cocoon. Some of the copper and blue species pupate among dry litter or stones.
Importance of Lepidoptera classification
In the same way that the question ‘How many butterfly species do we have?’ is important, how we decide whether an insect is a butterfly or a moth is important. If we don’t know what we’ve got, we won’t be able to measure, study or observe it in the future.
Nature of science
Classification is a tool used by scientists to show how organisms are related to each other and to group them by their characteristics. Butterflies and moths share the same kingdom, phylum, class and order. From there, they split into families based on their different physical characteristics.