Not a Butterfly
"What is this butterfly?" This query is often directed at Queensland Parks and Wildlife staff. Invariably the insect in question has large wings patterned with bands of black and pale blue which is often tinged with a coppery blush. It has been seen fluttering around flowers but cannot be found in any of the Australian butterfly books or butterfly posters.
The reason is simple; it is not a butterfly, but a moth - the appropriately-named day-flying (or zodiac) moth. So what makes this insect, which looks and acts like a swallowtail butterfly, a moth?
There are two main distinctions. All butterflies have antennae with club-shaped ends while those of most moths are feathery or pointed although some moths with clubbed antennae break this rule. In addition, while many moths possess a device (frenulum) to lock the wings together in flight, with one exception* this is not found in any butterflies. Butterflies, therefore, have clubbed antennae and lack frenulums.
The similarities between moths and butterflies. however ever, are more striking than their differences. the name of their order - Lepidoptera - which means 'scale wings', describing a unique characteristic common to all members of the group. In fact butterflies are just one of many groups y within the order, just as owls and parrots are all birds. Nevertheless, many people who consider butterflies a delightful asset to the garden, view moths as pests, to be exterminated. While a few species certainly are a nuisance, their larvae feeding on clothes, stored grains and crops, the vast majority of moths are completely innocuous. Indeed, many are important plant pollinators and a few have been put to good use, one species having devastated weedy invasions of prickly pears and another being used (along with weevils) in the fight against water hyacinths.
Of the estimated 22 000 Lepidopteran species in Australia, only 385 are butterflies, leaving about 21 615 moths! They range from the huge Hercules moth to the thousands of tiny 'microlepidoptera', most of which have not yet received names. A glance at a moth book will reveal how diverse and how lovely these insects can be. They are certainly worthy of the sort of appreciation which butterflies receive.
The four o'clock moth is another bright day-flying moth, frequently mistaken for a butterfly. It has a fat yellow body and attractive very dark purple wings interspersed with scaleless, transparent 'windows' and bright yellow spots on hindwings.
*The male regent skipper (found in the Wet Tropics) is the only butterfly to lock its fore and hindwings together during flight - which makes it the most primitive of the world's butterflies. The males, however, are more advanced - they have lost their frenulums!
(Source: Environmental Protection Agency.)
The life cycle of the butterfly is a miracle of nature which is introduced to us all early in our primary school careers - but details of the transformations involved still puzzle scientists.
Crawling eating machines
Before she lays her eggs, the female butterfly or moth must receive the correct chemical cues from the plants she lands on and uses receptors in her antennae, legs and the tip of her abdomen to test for them. Some females respond to a green surface by drumming with their feet. This is thought to abrade the leaf enough for the essential oils to be released and its suitability for egg-laying assessed. Temperature, colour, light, shade and leaf texture may also be important while low or high air pressure are known to influence egg-laying. Numbers of eggs laid by individuals vary from 120 to several hundred.
Most butterflies are very limited in the variety of plants which they consider suitable for their offspring, and the few chosen by each butterfly species are likely to be related. This is why some introduced plants, which apparently give the correct signals, are rapidly adopted (for example. the orchard butterfly on citrus, the common Australian crow on oleander and rubber vine). This can lead to some unfortunate young shoots of avocado, Eichhom's crow on frangipani and birdwings on non-native Aristolochia vines - but their caterpillars do not survive. On the other hand, the orchard swallowtail has been tricked, experimentally, into laying
Feeding machines, caterpillars can, in just two weeks, grow to 3000 times their original weight - the equivalent of a human ballooning to the size of a small elephant in the same period. It pauses only to shed its skin as it gets too tight, the number of costume changes depending on species but usually numbering about five. (Females may moult one more than males.) It has been shown that the eyes of some caterpillars are able to distinguish shape and limited colour - yellow and green stimulating feeding and blue and red having the opposite reaction. Behind the head of the caterpillar, the three-part thorax has six pointed legs. Further along the abdomen is a serious of stumpy legs used for hanging on. If pressed on to a smooth surface they can work as suction cups but they also have tiny clinging claws.
While living plants are the most normal caterpillar food, some species (particularly moths) eat dead wood. leaves and bark, stored seeds and cereal animal dung, wool, hair, feathers, other insects and each other. Among the plants, fungi, lichens mosses, cycads and even certain ferns* are targeted by a few species. Many caterpillars eat their own eggshells as their first meal although, since the proteins are indigestible. the benefit of this is not fully understood.
*Ferns are generally avoided by caterpillars - possibly because they contain a chemical similar to the moulting hormones of insects which could interfere with their development.
Change of life
When the caterpillar is ready to pupate it usually spins a silken pad for support. This is a particularly vulnerable time from the point of view of parasites. when it has slowed down but still ha!
Although some butterflies (and moths) pupate in underground chambers most hang from twigs or leaves. Two types of pupa (or chrysalis) are produced. Some species swallowtails. whites' yellows, blues, coppers, and some skippers) produce a girdle which is looped around the upper part of the caterpillar and provides support as its split skin is cast off. Special claspers (cremaster) or anal hooks at the end of the abdomen are then hooked into the silken pad. to hold the pupa secure. Other species simply hang upside down from the cremaster (which requires some fancy footwork when the skin is slipped oft). A number of moths enclose their pupa in silken cocoons - the silk me taking this to extremes.
Within the pupa great changes are taking place out of sight. When the caterpillar was originally forming inside the egg. two types of cells developed. Some formed clusters and ceased developing. while the others divided normally produce the body of the caterpillar. After it hatched these cells grew and enlarged as the caterpillar did to many times their original size, while
The colour of the upperwing of the female purple azure butterfly seems to be affected by humidity; those from Townsville are bluer while those from the more humid Cairns area are more purple.
Whereas caterpillars focus on little other than food, adult butterflies and moths have their minds firmly on sex.
Apart from a search for the occasional snack, adult butterflies have eyes only for each other. Generally it is the males which do the hunting - and have slightly larger eyes through which they keep watch for the appropriate colour, shape and size.
Some males, such as birdwings simply frequent the larval food plants waiting for females to appear. They may even pounce on females which have just emerged from the pupae, mating with them before their wings have completely dried.
Others having special trysting spots Males of many species - skippers, swordtails, triangles, jewels and azures - congregate on the tops of certain hills. Some patrol the area while others adopt perches which they defend vigorously, challenging other males which fly near . If one is removed it is quickly replaced, an indication of the popularity of certain perches. The hill top attraction is not a source of nectar or even larval foodplants, since they are usually absent, but virgin females, fresh from their pupae, which visit the area specifically for mating. With little time to be wasted in looking for a mate, this system is an efficient energy saver.
Odour is an important cue for nocturnal insects and many female moths produce a strong phenomena which can be detected by the feathery antennae of the males as much as 11 kilometres away; at this distance there would be as little as one molecule in every cubic metre of air. When the males have followed the scent to its source they too produce pheromones which may encourage the female to mate.
Butterflies also produce pheromones but in this case it is just the males v, which put on the perfume. It is produced in modified scales or pouches on the wings, structures on the abdomen or on a bundle of hairs which can be extended Suspended animation from the tip of the abdomen. Known as 'hair-pencils', these are generally covered with a dust-like scented powder which is sometimes applied to the brushes when the male inserts his hair-pencils into the patches or pockets on his wings. The dust acts as an aphrodisiac on females of the same species. When a male encounters an appropriate female he flies above her, raining his 'love-dust' on to her and sometimes attempting to brush her head and antennae with his hair-pencils. As a result a receptive female often settles and mating proceeds.
The chemicals from which the pheromones are manufactured are not present in the caterpillar food plants or in adults which have just emerged from their pupae. Instead the males must obtain them by feeding on the correct plants.
After mating the males of big greasy and glasswing butterflies ensure paternity of the offspring by depositing a special substance over the female's genitalia. This hardens to form a type of 'chastity belt' which prevents further mating.
Some adults do not have mouthparts to distract them from their primary task of finding a mate. Others sip only a little sugar and water (they are unable to digest fats or proteins) obtained from nectar or fermenting fruit juices. They, have sensitive chemoreceptors on their feet which have been shown capable of distinguishing between subtle differences in strengths and types of nectar solution. This food is used to fuel mating and egg production.
Wanderer butterflies are famous for their north American migrations where, known as monarchs, they travel vast distances and aggregate in spectacular numbers. The wanderings of this butterfly eventually brought it across the Pacific to Australia by late last century after as larval food plants were introduced. Old habits die hard and overwintering clusters have been observed in southern Australia.
There are migration records for about 30 species of Australian butterflies, although only 10 do so regularly. Brown awls, a type of skipper, migrate in their thousands, spending the winter in north-east Queensland and moving south in summer. The next generation makes the return trip north in late summer. During winter, a number of Wet Tropics butterflies move to the coast, and to sheltered areas along creeks, where they congregate in clusters of hundreds or even thousands for three months or more. Blue tigers and common Australian crows
Zodiac, or day-flying, moths can sometimes be seen in large numbers in winter, aggregating at night. It is thought that they may be heading to the Bartle Frere/Johnstone River area to breed. The adults disperse in summer large numbers having been seen in some years in December on the Atherton Tablelands.
Migrating adults generally do not eat, having built up sufficient fat reserves during their caterpillar stages. Their hormones are also 'switched off which means that they do not mate and are not bothered by territorial aggression which would make it difficult for so many to live so closely. Butterflies are able to go into a form of hibernation at any stage - egg, caterpillar, pupa or adult. Growth, below a certain temperature (which varies with species) may cease, only to resume when the temperature rises again. Drought and lack of food may also cause development to cease, as can shorter days. If dingy, orchard and canopus swallowtail caterpillars are exposed to less than 14 hours of light per day, no matter how warm it is, development pauses at the pupae stage. The fivebar swordtail butterfly, which frequents deciduous vine forests, flies only in summer. It rests in its pupa for the remainder of the year, emerging in response to summer rains.
If a butterfly is too cold to fly (20deg. is about the limit) it may flap or vibrate its wings to warm up. Overheating can also be a problem, particularly in the tropics, so many species fly or rest in shade and when they land hold their wings upright so that they partially shade the body.
Made up of many lenses, an adult butterfly's eyes are a vast improvement on those it possessed as a caterpillar and are particularly sensitive to movement and colour. Experiments with paper flowers have shown that certain butterfly species prefer blue to purple and yellow to red, ignoring green until they were ready to lay eggs. At least some species are able to see ultraviolet; when viewed in this light, the wings of some male white butterflies, can be seen to have iridescent patches which are invisible to us but presumably play an important part in courtship.
(Source: Environmental Protection Agency.)
Butterflies, moths and their caterpillars are an important part of the food chain, providing tasty snacks for many other animal, from birds, bats and reptiles to invertebrates such as spiders. Many are parasitised by flies and wasps whose young feed on eggs, caterpillars and pupae. However, some must make it through to adulthood to produce the next generation - and use some intriguing strategies to get there.
Many caterpillars and moths operate under cover of darkness, hiding away during the day. Alternatively, a number of caterpillars create cover for themselves by joining adjacent leaves together or by folding or rolling leaves and securing their homes with silk. Small caterpillars (leaf miners) may tunnel inside their foodplant leaves while larger ones, such as the witchety* grub, (a wood moth caterpillar) burrow deep into wood and roots. Caterpillars of the Australian plane butterfly live in the fruits of the lolly berry vine (Salacia chinensis), eating the seeds.
*The original 'witchety grub' is the larva of the wood moth Xyleutes leucomochla, which lives in acacia roots in inland South Australia. The term is now used widely for many edible woodboring caterpillars and beetle larvae.
Camouflage is frequently employed. Green caterpillars vanish against a leaf background and some moths merge wonderfully with their background when they land on bark and lichen, pressing their wings down flat to eliminate shadows. Some have tufts of scales which resemble rough bark and are able to orient themselves so that their markings match those of their background.
Young orchard butterfly caterpillars, and certain moths, rather than merging with their background, pass themselves off instead as bird droppings, which they resemble in both form and colour.
If a predator penetrates the bird-dropping disguise off the orchard butterfly caterpillar it is in for a surprise when suddenly confronted with a pair of bright red horns which pop up from the creature's head. All swallowtails birdwings Ulysses and so on) are able to perform this trick when disturbed. The 'horns', known as osmeterium, not only shock with their unexpected colour (which varies from pink to yellow and orange) but produce a strong odour which presumably also acts as a deterrent as the caterpillar waves its head at the source of the disturbance. Since birds are particularly sensitive to the colour red, it may be designed to repel them, but the smell is thought to also repel insects and act against potential parasites such as wasps. Some moth caterpillars also have pop-up osmeteriums. sometimes producing formic acid as well.
The stinging hairs on the caterpillars of some moth species. notably the bag or boree. moth. create another effective defence. the toxins in the hairs causing pain and itchiness. While this no doubt repels many birds, cuckoos and cuckoo shrikes seem to be immune and feast happily on these larvae. Many of these caterpillars congregate in a silken fortress in, or at the base of, a tree a formidable defence since the cast off skins and hairs permeate the bag. Hairy caterpillars may move, en masse, in a long snake-like procession which may just be mistaken for one by potential predators.
Some caterpillars, when disturbed, simply drop out of sight literally - using a silken thread to lower themselves below the foliage until the coast is clear and they can return to base. Others wriggle wildly and attempt to strike predators and parasites.
Some moths can avoid capture in spider webs and on sticky sundew traps by sacrificing some of their scales - a loss which does not affect their ability to fly.
The Australian leafwing butterfly is named for its imitation of a dead leaf, the projecting part of its hindwing looking like a stalk while a dark vein running across both fore and hindwings resembles a leafs midrib. Although orange above, this species clamps its wings shut when it settles in shade, instantly becoming a 'dead leaf. The evening brown (right) also merges well with the dead leaves on which it frequently settles while many blues perform perfect disappearing acts, the pretty colours of their upper wings vanishing as soon as they settle and close them, to expose just the dull underwings.
If camouflage fails, and a predator is about to take a bite, many adult moths and butterflies as well as the caterpillars have a surprise up their sleeve. Bright colours and/or patterns, suddenly revealed from beneath a moth's dull upper wings at the moment of flight, may cause a startled predator to retreat.
Large eye spots, especially if they also make a sudden appearance and open and close as the insect flies, can cause the attacker to consider its own safety - has it disturbed a sleeping owl or, in the case of an eye-spotted caterpillar, a snake? The eyespots on some caterpillars are hidden in a crease in the skin unless it is disturbed. Alternatively, spots may serve to attract an attack to a part of the wing, or the tail end of the caterpillar, enabling its owner to escape with less than fatal damage.
Pupae (cocoons and chrysalises), being stationary, are vulnerable to attack. The tough easing provides some protection and most are extremely well camouflaged but in addition to this many are surprisingly capable of animation - twitchings often accompanied by clicks 9 and rattles, created by contractions of the abdomen.
The noises are produced when certain abdominal segments, equipped with special ridges, are rubbed together or against ridges within the pupa. Since this is usually a response to the pupa being touched, it is presumably a strategy for startling predators. Clicking, however, is particularly common in species which are attended by ants (see right). Probably it attracts them, eliciting defensive behaviour on the pupa's behalf - or the pupa may act as an alarm bell, alerting the ants to intruders.
In contrast to those butterflies and moths which rely on camouflage, the bright wings and colourful stripes and adornments of many species would seem to invite predators. Most predators, however, know better. They know that red (along with orange or yellow, combined with black) means danger.
A disproportionate number of caterpillar food plants contain toxins. It is thought that while the plants were evolving toxic defences against being eaten, the butterflies were evolving alongside, developing resistance and turning the chemical weapons to their advantage. Retained through the process of metamorphosis, the poisons serve not only the caterpillars, many of which demonstrate their unpalatability with bright stripes and spines, but also the colourful and carefree adult butterflies. (The toxins are also found in eggs, as well as in some wasps which have parasitised certain moth caterpillars.) Observations of adult wanderer butterflies have shown that the toxins they have acquired from milkweeds - a type of heart poison which affects vertebrates - will quickly cause a bird which attempts to cat them to vomit. It does not necessarily die, but lives to remember and not repeat its mistake. Interestingly the poison is most concentrated in the wings and is thus quickly discovered by a bird as it begins an attack.
Many tiger moths can pre-empt an attack by producing. with a sizzling sound, a pungent, toxic frothy substance from the sides of their heads while certain moth caterpillars spit repellent liquid at enemies. This liquid is extracted from their food plants and stored, ready for use, in a special part of the gut.
The common Australian crow butterfly, which feeds on native figs and hoyas, was quick to adopt the notoriously toxic oleander as a food plant, when it was introduced from the Mediterranean. Perhaps its unusually obvious pupa, of a burnished silver or gold appearance, is designed to advertise its unpalatability. Aristolochia vines, eaten by birdwing, red-bellied swallowtail and big greasy caterpillars, are also toxic. Not all poisonous butterflies and moths acquire their toxins from food plants, however. Some are able to manufacture these themselves - certain moths can produce toxic substances such as cyanide.
While many bright butterflies are toxic - and advertise it some which are not take advantage of this by mimicking their companions' colours and patterns. During the course of evolution it is possible that the butterflies which most closely resembled the poisonous ones were those most likely to survive, this chance gene being transmitted to the next generation and so on. This strategy is only successful, however, if the poisonous butterfly is more common than its mimic - otherwise neither species benefits as predators realise that some are edible. In Australia, although this strategy is not especially common, the toxic lesser wanderer butterfly is mimicked by the female (but not the male) danaid eggfly and it is thought that the black and white aeroplane benefits from its similarity to the toxic Cairns hamadryad. In New Guinea a swallowtail butterfly mimics the poisonous zodiac (day-flying) moth.
It is also possible to consider the dingy swallowtail big greasy butterfly and red-bellied swallowtail as mimics since they look very similar. All feed on Aristolochia vine leaves so all three may be projecting a common 'don't eat me' message to which they all contribute. The similarity of all the toxic Australian crows no doubt produces the same joint benefits.
A number of brightly red moths such as this tiger moth, look rather like similarly bright wasps and no doubt escape attack from animals which do not wish to be stung. Some night-flying moths have organs which function as ears and allow them to detect the ultrasound of insectivorous bats and thus avoid them. Some tiger moths are able to produce their own ultrasound which is the audible version of the bright colours of the day-flying insects and warns bats that they are not good to eat. Their clicks may even block the bats' sonar.
Most butterflies in the blue group (Lycaenidae) have a special relationship with various species of ants. The ants feed on a sugary substance which the caterpillars produce from special glands in their skin, often when stimulated by the ants' antennae. This sugar hit may simply prevent the ants from eating the caterpillars. (Ant-attended caterpillars have particularly thick skins, which may also protect them from these potential predators.) However, it is presumed that the ants actively defend the caterpillars in return for this 'protection money'. The and bodyguard is not entirely effective because many of the blues are attacked and killed by parasitic wasps and flies. Nonetheless, the relationship is a close one and, although some species fraternise with ants on a casual basis, some species do not thrive when separated from their keepers. Indeed, if the sugary fluid is not removed the caterpillars are in danger of becoming fatally mouldy.
The adult butterflies, when laying eggs, seek out the presence of ants as well as the correct food plant. When they have hatched, the little caterpillars are often carried by the ants into their nest, or stowed in specially built shelters, where they are pampered - cleaned and cared for and possible even fed. Even green tree ants, which normally do not hesitate to eat many caterpillars, turn of their aggressive instincts when caring for certain species of blues. As they grow, the caterpillars are carried out at night to their foodplant. (These butterflies have been observed to feed on an unusually large range of plants.
When some caterpillars and even pupae were experimentally removed and placed a few metres from home, their ant guardians carried them back again.
The Apollo jewel butterfly has a close relationship with the ants which inhabit ant plants - bulbous epiphytes which can be seen growing on many coastal rainforest trees and which provide tunnels in which the ants nest. The Apollo jewel caterpillar also lives within the ant plant, emerging at night to feed on its leaves. Thus a complicated partnership exists between the ant plant, the ants and the butterfly - and the tree on which they all hang.
Some species are not very grateful. Caterpillars of the ant-blue butterflies eventually turn against their protectors and eat the ant larvae, while the moth butterfly caterpillar arrives, entirely uninvited, in an ants' nest when it also feeds on its unwilling hosts' babies (right). In this case the victims are the very aggressive green tree ants, but they are powerless against the exceptionally thick and flattened skin (left) which renders this caterpillar invulnerable. After pupating within its bunker, the adult is able to escape unscathed, abundant disposable scales on its wings and body dislodging as the angry ants attempt to cling to it.
(Source: Environmental Protection Agency.)