Flying under the radar

By Ann Graeme

Moths are the poor cousins of butterflies. We notice and admire butterflies, flitting about on their gaudy wings in the sunlight, but we tend to overlook the secretive moths of the night. What a world we are missing!

Moths vs Butterflies

Butterflies and moths are not that simple to tell apart.

General points of difference are:

  • All butterflies fly by day; most moths fly by night.
  • Butterflies always have slender antennae with a knob on the end.
  • Moth antennae come in all shapes and sizes, often bushy and branched or feathery, but some moths have antennae like those of butterflies.
  • Most butterflies (and some moths) rest with their wings raised like sails.

Most moths wrap their wings around their bodies, fold
them like roofs or spread them out
flat (as do some butterflies).
However carefully you pick up a moth,  it will leave a dusty imprint
on your fingers. These are its
scales, which cover its wings
and body like tiles on a roof,
giving it colour and pattern and
sparkle. Butterflies and moths
are the only insects covered
like this, and it gives them their
family name, Lepidoptera,
which means “scaly wings”.
the radar

Butterflies may be more colourful but moths have a subtle beauty all their own.

New Zealand has 1684 named species of native moths and perhaps another 200 yet to be named.

We have far fewer butterflies – just 15 natives and another seven, including the monarch and cabbage white, which are not native but live and breed here.

Moths and butterflies are the adults of their species. Like all adults, they are preoccupied with sex for to them falls the responsibility of procreating their species. To do this they must find a partner – and stay out of the clutches of predators like hungry birds.

Staying safe involves various strategies. You can advertise that you are inedible – like the monarch butterfly – you can come out at night; or you can adopt a disguise. Moths favour the darkness and they are champions at daytime disguise.

But in disguise and in the dark of night, it could be difficult to find your partner. Moths may not see very well but they have an extraordinary sense of smell – not through their noses, of course, since invertebrates don’t have noses, but through their antennae. A TV antenna has many stalks and struts to increase its receptive area.

For the same reason, the moth’s antenna is branched and feathered, especially the male’s because he has to find his partner.

She will emit a chemical pheromone to lure him. So potent is her scent and so perceptive are his antennae that he will smell her from several kilometres away!

All this sex and distance flying takes energy, and moths refuel by sipping the nectar of flowers. Native moths are adapted to feeding from native flowers and act as important agents for their pollination. White is the most visible colour at night so many of our insect-pollinated native plants have white flowers.

They are often strongly scented, and their scent may become even more powerful after
dark and in the damp night air.

But if the purpose of an adult moth is sex, the priority of its caterpillar is food. This is a remarkable division of labour – a triumph of form matching function.

While an adult moth is a flying sex machine, its caterpillar is a stomach-on-legs.

The caterpillar will eat and eat and eat … until it has stored sufficient energy to become a pupa, where its caterpillar tissue will be reassembled into an adult.

Caterpillars eat vegetable matter including leaves, flowers, stems, wood, forest litter, lichens and fungi.

Some feed on a wide variety of different plants but most species are very choosy.There are a number of tiny moths known as leaf miners. Their caterpillars don’t chew ragged holes but make tunnels inside the leaf.

The astelia leaf miner caterpillar lives underground in the bulb of the astelia plant. It chews its tunnels in the soft green tissue of the growing leaves before they emerge above ground.

Long after the caterpillar has pupated and hatched into a moth, the evidence of its work remains. Above ground, the old tunnels leave zigzag patterns on the leaf, widening in geometric precision as the leaf lengthens.

Some plants host several species of leaf miner caterpillars and an experienced lepidopterist can identify them from the distinctive shape of their tunnel.

Being fussy about the plants they eat means different species of caterpillar occupy discrete niches and do not compete with one another.

Even when species share the same food plant, by eating different parts of it in different ways they still avoid competition and so the range of niches is extended even further.

This explains how our forest and alpine shrublands can support such a huge diversity of native moth species.

Two species eat only flax leaves. The flax notcher caterpillar eats notches out of
the leaf margin.

The flax looper caterpillar in the field eats windows in the leaf, closer to the mid-vein, so the feeding territories of each species don’t overlap.

This is good for the moth species as their caterpillars don’t compete for food – but hard on the flax leaves!

The largest family of moths in New Zealand is the Geometridae, with more than 285 species. Their caterpillars have true legs at the front, false or pro-legs at the back and a long, unsupported body in between.

They move by stretching out the body and then drawing it into an omega-shaped loop Ω. Americans call them inchworms as
they seem to measure the twig they are walking on. We call them loopers.

Species of looper caterpillars eat a wide variety of native plants including many different ferns. The zigzag fern looper eats the common shield fern, the silver fern looper eats silver ferns and the pale fern looper is cosmopolitan,
eating silver fern, soft tree fern, prickly shield fern, maidenhair ferns and more.

These moths and their caterpillars are all part of the intricate biodiversity of our native ecosystems. They make little impact on our lives, unlike some introduced moths which are much less welcome.

The caterpillars of the codlin moth ruin our apples and those of the Indian meal moth make a nasty surprise in the foodstuffs in our pantries.

But we can use these moths’ own weapons against them. A sticky card baited with the particular moth pheromone will lure each of these pests to their deaths, a gruesome but effective strategy.

But don’t let them prejudice you against moths. We have a glorious array of endemic, attractive and interesting species and they are well worth a second look.

Forest & Bird North Shore branch chairperson Alan Emmerson gave extensive assistance with this article. With Robert Hoare and Birgit Rhode of Landcare Research, Alan is preparing a comprehensive guide to the larger moths of
New Zealand.

It will be available as a book and online.
See www.landcareresearch.co.nz Photos: Birgit Rhode/Landcare Research