Atlas Moth
Attacus atlas
The atlas moth has the sort of scale that changes how you look at it. The wings are enormous, but it’s often the smaller details that become interesting once the initial impression wears off. There are translucent windows through all four wings, heavy bands of rust, brown, cream and black, and forewing tips stretched into shapes often compared with a snake’s head. Then there’s the adult moth itself, living on energy it collected weeks earlier as a caterpillar. It has no functional way to eat.
Classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Lepidoptera
Family: Saturniidae
Genus: Attacus
Species: Attacus atlas
Common Name: Atlas Moth
Where Giants Take Wing
Attacus atlas is native to parts of South, Southeast and East Asia, with a range extending from India and southern China through much of Southeast Asia, including Thailand, Malaysia and Indonesia. Tropical and subtropical forests provide the warm conditions and larval food plants the species needs, although atlas moths aren’t confined to untouched forest. They can also occur around woodland edges and cultivated areas where suitable plants remain available.
They aren’t native to Australia. We do, however, have large saturniid moths of our own, including species of Coscinoceraand Opodiphthera.
Wings Made to Be Noticed
Atlas moths are among the world’s largest moths, particularly by wing surface area. Large individuals can span more than 20 cm, with females generally broader and heavier than males. A female’s abdomen is especially substantial because she’s carrying eggs.
The wings themselves are difficult to reduce to one colour. Chestnut and reddish brown move through black, cream and softer pinkish areas, with the pattern becoming particularly busy towards the margins. Cutting through all of that colour are the clear windows. They can look almost like pieces of thin glass have been set into the wings.
They haven’t. These areas have few or no scales, exposing the transparent wing membrane beneath. Against a dark background the windows can almost disappear into empty space. Hold the moth towards light and they become something else entirely.
Sex is often fairly easy to recognise as well. Males have large, heavily feathered antennae, while those of females are narrower. The difference isn’t decorative. Those broad male antennae are highly sensitive to the pheromones released by females.
Eat First, Fly Later
An atlas moth begins life on a leaf, where a female lays rounded eggs on plants suitable for the larvae. The caterpillars that hatch are pale green, eventually becoming thick bodied and surprisingly substantial themselves. Their fleshy projections often carry a pale, powdery coating that gives them quite a different appearance from the adult they’ll become.
Atlas moth caterpillars aren’t tied to one food plant. Recorded hosts include citrus, guava, cinnamon and other Cinnamomum species, alongside several other trees and shrubs across their range. This is the stage devoted to eating. Leaves are converted into growth and, eventually, the reserves the adult moth will have to live on.
Once fully grown, the caterpillar spins a tough, papery silk cocoon, often among or attached to leaves. Metamorphosis takes place inside. When the adult emerges, its wings are still small and soft and must be expanded with fluid before they harden into their final shape.
Then the clock is already running.
Living on Borrowed Time
Adult atlas moths have reduced, non-functional mouthparts. There are no flowers to visit and no late meal to replace the energy spent flying or producing eggs. What the caterpillar stored is what the moth gets.
Adult life is consequently short, generally around one to two weeks. Females tend to remain comparatively still after emerging and release pheromones to attract a mate. Males do more of the searching, following those chemical signals with the help of their feathered antennae.
After mating, the female lays eggs over several nights. Neither sex can replenish what it spends along the way.
It’s an odd division when you stop to consider it. The caterpillar spends its life feeding and growing but can’t reproduce. The moth can reproduce, has those extraordinary wings and can move through the world in an entirely different way, but it can’t take another bite.
A Snake at the Wingtip
The forewing tips deserve a closer look. They extend away from the main body of the wing and carry dark markings bordered with lighter colour. From the right angle, the resemblance to a small snake’s head is difficult to miss.
These tips are widely interpreted as defensive mimicry that may discourage predators from attacking a resting moth. It’s an appealing explanation, and the resemblance is certainly striking to human eyes, but the behaviour of potential predators is harder to reduce to such a tidy statement. Describing them as snake like is straightforward. Establishing exactly what another animal sees in them, and whether that resemblance changes its decision to attack, is more complicated.
The comparison has nevertheless become one of the atlas moth’s most recognisable features, despite occupying only a small part of an otherwise enormous wing.
Wrapped in Wild Silk
The cocoon has attracted human attention too. Atlas moth silk isn’t the same material encountered in conventional commercial silk production. The domesticated silkworm, Bombyx mori, produces the fine continuous filament most readily associated with silk textiles, while Attacus cocoons produce a coarser wild silk.
Atlas moth and related wild silks have been collected and used on a smaller scale in parts of Asia. The cocoon itself gives some indication of the difference. It’s brownish, tough and papery rather than the smooth white form most people picture when they think of a silkworm cocoon.
In the Apotheca
It’s easy for the size of an atlas moth to swallow everything else about it. A spread specimen changes that once you get close enough. The windows interrupt the scales completely, the outer margins contain far more colour than they first appear to, and those peculiar forewing tips suddenly occupy a surprisingly small proportion of the whole moth.
The antennae are another detail worth lingering over. Put a male and female beside one another and the difference is immediate, even before the fuller female abdomen is considered. It’s one of those comparisons that makes sexual dimorphism considerably easier to understand than a written description ever could.
An atlas moth is simply too large to take in neatly. Your eye moves around it instead. Across one wing, through the transparent windows, back towards the body and antennae, then out again towards the tips. For something so often remembered because it’s enormous, there’s an awful lot happening in the smaller details.
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