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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