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Introduction
to Lepidoptera
(Butterflies and
Moths)
Butterflies and moths are
insects (INSECTA), a division of the Animals called a CLASS.
The Class Insecta is notable for the adults possessing a
body consisting of three segments (head, thorax and abdomen), six
legs and, in most cases, one or two pairs of wings, thus enabling
flight to take place. The INSECTA is divided into approximately
24 groups called ORDERS and Butterflies and moths belong to the
Order LEPIDOPTERA, which means 'scale-winged'. The Lepidoptera
are considered one of the 'higher' orders of insects and are placed
between the Caddisflies (Trichoptera) and Bees and Wasps
(Hymenoptera). The Order is further sub-divided into the
larger and smaller members of the group and called Macrolepidoptera
and Microlepidoptera respectively. This is rather an arbitrary
division since many so-called 'Micros' are far larger than some
of the 'Macros'. Butterflies and moths are usually treated separately
and Butterflies are known as Rhopalocera (Club-horned ) and
moths Heterocera (Varied-horned). This, again, is rather
a rough division as the two groups show intermediate types of antennae
which makes distinction on this feature occasionally very difficult.
These insects are well-known for their beauty in colour and pattern
of their wings. The colour is a result of layers of scales which
clothe the wings, the scales having innumerable patterns and producing
colour in the form of pigmentation or light refraction. The latter
is particularly prominent in the irridescent blue butterflies of
the family Morphidae of South America.
Lepidoptera
undergo what is known as a 'complete metamorphosis'. This consists
of four very distinct stages - Egg (Ovum), Caterpillar (Larva),
Chrysalis (Pupa) and Adult (Imagine). Apart from overwintering stages,
the larval stage is usually much the longest and where the main
part of development and acquisition of nutrients takes place. Larval
food consists of vegetable matter of most kinds, depending on the
species of insect. Leaves of trees and plants are the usual parts
eaten, but flowers, dead vegetable matter and live timber or internal
parts of woody plants are all utilised.
Mortality amongst all
stages of Lepidoptera is very high and it is probable that
no more than 1% of ova laid ever reach maturity. Predation by other
forms of animal life, including insects, accounts for a large proportion
of losses. Many predators such as birds are far larger than insects
and therefore need large numbers to satisfy food demands. The breeding
season of birds coincides with the maximum number of lepidopterous
larvae and species such as the Blue Tit (Parus caeruleus
Linn.) feed several thousands to their nestlings every day. Such
birds are considered beneficial in controlling populations of insects
which may harm fruit and woodland trees. Less obvious predators
are internal larval parasites, usually the larvae of Flies (Diptera)
or Wasps (Hymenoptera). In the case of the latter group,
the female possess a long ovipositor resembling a sting. This is
pushed through the skin of a larva and an egg laid internally. The
resulting larva of the wasp then feeds on the food supplies of the
host larva. However, to avoid committing suicide by starvation,
the wasp larva feeds in non-lethal parts of its host until it is
full grown.
To ensure the survival
of species of Lepidoptera many strategies have evolved to
overcome high death rates. Females of most species lay many ova.
To enable a female to do this most efficiently, males usually hatch
several days before the females. This ensures that a mate is awaiting
a female on emergence and she does not have to spend time awaiting
fertilisation and the chance of being eaten before egg-laying. Males
are also much more abundant and active which helps ensure that no
female remains infertile. Females emit scent in the form of pheromones
which are extremely attractive to males, so much so that some male
species can smell a female at a range of three kilometres. Several
broods may be produced in one year and in the Tropics species may
be continuously brooded. Larvae have adapted many shapes and colours
to avoid detection. Many of the larvae of the Geometridae
are elongated in shape and, with various protuberances along the
body, can appear to be twigs on their foodplant when brilliantly
camouflaged and lying motionless at rest during the day. Other species
have developed other strange camouflage techniques. One is to look
like something unpleasant such as a bird dropping. In this case
the larva makes no attempt to hide but sits curled up on a leaf
looking like a bird dropping. Provided it stays motionless during
daylight hours, it is safe. Pupae are usually protected by being
underground or in a cocoon made of tough silk, often with irritant
hairs from the larva sewn into the silk, which would make a very
unpleasant meal for any predator.
Adults also have many
forms of protective patterns and coloration, probably the most striking
and best known of these are types of mimicry. The larvae of many
of the butterfly family Danaidae live on and are able to
ingest the toxins in some poisonous plants. This poison passes to
the adults which, though day-flying, are avoided by bird predators
who soon learn by bitter experience the species to be left alone.
Other butterfly species of completely different families, notably
the Swallowtails (Papilionidae) have evolved wing shapes
and coloration to match the poisonous model. This rather simplified
account is an example of Batesian mimicry, first described by H.W.Bates
in the 19th C. Large eyespots, often displayed when alarmed, is
another method of discouraging predators. The large and bulky Hawkmoths
(Sphingidae) include species such as the Death's-head Hawkmoth,
not only well-known for the skull and crossbones pattern on its
thorax, but with the ability to squeak fairly loudly when disturbed.
Butterflies and moths
are very numerous in species and numbers, with about 140,000 named
species and many more to be discovered in some of the remote and,
especially, in the tropical regions of the World. Britain has about
2,500 species, which is a small total compared with Continental
Europe. Besides Britain having cold winters, during which lepidoptera
have to aestivate in one of their four stages, this country is an
island and subjected to moist westerly winds. The combination of
low temperatures and moisture is not conducive to high insect biodiversity.
It is significant that, of the 2,500 species in Britain, only about
50 are butterflies, the group which need sunshine for optimum activity.
Though insects comprise
about three quarters of all known animal species, they receive little
attention unless causing problems to Man. Because the larvae of
most butterflies and moths are vegetable feeders (Phytophagous)
many fall foul of humans by eating their crops and possessions.
A good instance is the group of 'Clothes Moths' (Tineidae)
long known from the habit of the larvae in eating woollen and cotton
garments. Because Man tends to grow crops in large fields of single
crops, it is inevitable that lepidoptera may produce themselves
to such an extent as to attack crops in 'plague' proportions. This
happens frequently in tropical regions. Because the evolution of
Lepidoptera has been closely associated with that of the higher
plants, we find many interesting life histories leading to 'Which
came first' questions.
One fascinating story
concerns the great naturalist Alfred Russel Wallace, a contemporary
of Darwin and joint founder of the Evolution Theory. Wallace was
on Madagascar in the late 19th Century and was intrigued by the
extremely deep honey tube in the corolla of an Angraecum
orchid. Since this was some 250mm. in depth, he postulated that
there must be an undiscovered Hawkmoth with a proboscis long enough
to be able to pollinate this plant. A few decades later, the moth
was found, a sub-species of Xanthopan morgani Walk., possessing
one of the longest 'tongues' (proboscis) of all insects. This sub-species
was named praedicta by Rothschild after Wallace's prediction.
This demonstrates the close link between plants and insects, in
this case, host specific to an extreme degree.
Apart from indirect
damage to Man, lepidoptera are harmless except for some members
of the moth Family Lymantriidae (Tussock Moths). Their larvae
are clothed in hairs and these can prove very irritant to human
skin. If any of the hairs come into contact with the face it can
cause severe swelling and may close up eyes. The message is to be
wary of hairy caterpillars! Rather than harm Man, some moths are
very advantageous to Him. The best example is the Silkmoth Bombyx
mori Linn.
This species has long beenb reared in Europe for its silk, though
native to China. Through domestication it has lost its power of
flight and it is now believed to be extinct in the wild. Some larvae
live inside tree roots and limbs and, because their weight is supported
by tunnels, can reach large sizes. The famous Witchety Grubs of
Australia are the best examples and are eaten raw or cooked on open
fires.
The voracious appetites
of larvae has been put to advantage in certain cases. Two serious
cactus pest species were introduced from the New World to Queensland,
Australia, early in the century and became such pest species that
an estimated 20 million hectares of cultivated land had become over-run
with the infamous 'Prickly Pear'. Larvae of the moth Cactoblastis
cactorum Berg (Fam. Pyralidae) were collected in Argentina
in 1926 and placed on plants in Queensland. The experiment was so
successful that the 'Prickly Pear' had been reduced to scattered
individual plants within a few years.
Much taxonomic work
has been done over the past 200 years which has resulted in our
present knowledge of species and distributions. Professional entomologists
have done much of the taxonomy but much of the collecting of data,
especially the insect specimens, has been done by large numbers
of amateurs and explorers. The most famous instance of early collecting
of specimens for research was that of John McGillvray, naturalist
aboard H.M.S. Rattlesnake exploring the Pacific Region in 1884-85.
Many butterflies fly high round the tops of trees and he resorted
to his shotgun to bring down the first known specimen of the giant
Birdwing (Ornithoptera victoriae Gray). Nowadays, techniques
for surveying and sampling species are more sophisticated with one
of the biggest improvements made in the 1950's with the introduction
of mercury-vapour lamps to attract night-flying moths. It is not
yet fully known why insects are so attracted to light, especially
ultra-violet light, but it is very effective given favourable weather
conditions and lack of moonlight, which seems to affect the attractiveness
of the light. Much has yet to be learned about the global lepidopterous
fauna but it is a field of natural history in which anyone can contribute
and enjoy a lifetime of constructive and fascinating study.
Bibliography
Bradley, J. D. (1998)
Checklist of Lepidoptera recorded from the British Isles. Bradley,
J. D.
and M. J.
Carter, D. (1992) Butterflies
and Moths. Dorling Kindersley.
Clapham, A. R., Tutin,
T. G., and Warburg, E. F. (1962) Flora of the British Isles, 2nd
Edition. Cambridge.
Kirby, W. F. (1903)
The Butterflies and Moths of Europe. Cassell and Co. Ltd.
Mansell, E. and Newman,
L. H. (1968) The Complete British Butterflies in Colour. George
Rainbird Ltd.
Rose, F. (1981) The
Wild Flower Key. Warne.
Seitz, A. (1914) The
Macrolepidoptera of the World, Vol. III. The Noctuid Moths. Stuttgart.
Skinner, B. (1988)
Colour Identification Guide to Moths of the British Isles. Viking.
South, R. (1973) The
Moths of the British Isles, Series I and II. Warne & Co. Ltd.
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Introduction
to Lepidoptera