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The Cambridge Manuals of Science and
Literature
THE LIFE-STORY OF INSECTS
CAMBRIDGE UNIVERSITY PRESS
London: FETTER LANE, E.C.
C.F. CLAY, MANAGER
[Illustration]
Edinburgh: 100, PRINCES STREET
London: H.K. LEWIS, 136, GOWER STREET, W.C.
WILLIAM WESLEY & SON, 28, ESSEX STREET, STRAND
Berlin: A. ASHER AND CO.
Leipzig: F.A. BROCKHAUS
New York: G.P. PUTNAM'S SONS
Bombay and Calcutta: MACMILLAN AND CO., LTD.
[Illustration: _Frontispiece._ Transformation of a Gnat (_Culex_).
Magnified 5 times.
A. Larva. (The head is directed downwards and the tail-siphon with
spiracle points upwards to the surface of the water.)
B. Pupal Cuticle from which the Imago is emerging. (The pair of
'respiratory trumpets' on the thorax of the pupa are conspicuous. The
wings of the Imago are crumpled, and the hind feet are not yet
withdrawn.)
C. Adult Gnat. Female.]
[Illustration]
THE LIFE-STORY
OF INSECTS
BY
GEO. H. CARPENTER
Professor of Zoology in the Royal
College of Science, Dublin
Cambridge:
at the University Press
New York:
G.P. Putnam's Sons
1913
Cambridge:
PRINTED BY JOHN CLAY, M.A.
AT THE UNIVERSITY PRESS
With the exception of the coat of arms at the foot, the design on
the title page is a reproduction of one used by the earliest known
Cambridge printer John Siberch 1521
PREFACE
The object of this little book is to afford an outline sketch of the
facts and meaning of insect-transformations. Considerations of space
forbid anything like an exhaustive treatment of so vast a subject, and
some aspects of the question, the physiological for example, are almost
neglected. Other books already published in this series, such as Dr
Gordon Hewitt's _House-flies_ and Mr O H. Latter's _Bees and Wasps_, may
be consulted with advantage for details of special insect life-stories.
Recent researches have emphasised the practical importance to human
society of entomological study, and insects will always be a source of
delight to the lover of nature. This humble volume will best serve its
object if its reading should lead fresh observers to the brookside and
the woodland.
G.H.C.
DUBLIN,
_July_, 1913.
CONTENTS
CHAP. PAGE
I. Introduction 1
II. Growth and Change 8
III. The Life-stories of some Sucking Insects 16
IV. From Water to Air 23
V. Transformations, Outward and Inward 35
VI. Larvae and their Adaptations 49
VII. Pupae and their Modifications 79
VIII. The Life-story and the Seasons 89
IX. Past and Present--the Meaning of the Story 105
Outline Classification of Insects 122
Table of Geological Systems 123
Bibliography 124
Index 129
LIST OF ILLUSTRATIONS
Stages in the Transformations of a Gnat _Frontispiece_
FIG PAGE
1. Stages of the Diamond-back Moth (_Plutella 3
cruciferarum_)
2. Head of typical Moth 5
3. Head of Caterpillar 5
4. Common Cockroach (_Blatta orientalis_) 12
5. Nymph of Locust (_Schistocera americana_) 13
6. _Aphis pomi_, winged and wingless females 19
7. Mussel Scale-Insect (_Mytilaspis pomorum_) 21
8. Emergence of Dragon-fly (_Aeschna cyanea_) 29-31
9. Nymph of May-fly (_Chloeon dipterum_) 33
10. Imaginal buds of Butterfly 39
11. Imaginal buds of Blow-fly 43
12. Carrion Beetle (_Silpha_) and larva 51
13. Larva of Ground-beetle (_Aepus_) 52
14. Willow-beetle (_Phyllodecta_) and larva 53
15. Cabbage-beetle (_Psylliodes_) and larva 54
16. Corn Weevil (_Calandra_) and larva 55
17. Ruby Tiger Moth (_Phragmatobia fuliginosa_) 61
18. Larvae and Pupa of Hive-bee (_Apis mellifica_) 65
19. Larva of Gall-midge (_Contarinia nasturtii_) 68
20. Crane-fly (_Tipula oleracea_) and larva 69
21. Maggot of House-fly (_Musca domestica_) 71
22. Ox Warble-fly (_Hypoderma bovis_) with egg,
larva, and puparium 75
23. Pupa of White Butterfly (_Pieris_) 85
CHAPTER I
INTRODUCTION
Among the manifold operations of living creatures few have more strongly
impressed the casual observer or more deeply interested the thoughtful
student than the transformations of insects. The schoolboy watches the
tiny green caterpillars hatched from eggs laid on a cabbage leaf by the
common white butterfly, or maybe rears successfully a batch of silkworms
through the changes and chances of their lives, while the naturalist
questions yet again the 'how' and 'why' of these common though wondrous
life-stories, as he seeks to trace their course more fully than his
predecessors knew.
[Illustration: Fig. 1. _a_, Diamond-back Moth (_Plutella
cruciferarum_); _b_, young caterpillar, dorsal view; _c_, full-grown
caterpillar, dorsal view; _d_, side view; _e_, pupa, ventral view.
Magnified 6 times. From _Journ. Dept. Agric. Ireland_, vol. I.]
Everyone is familiar with the main facts of such a life-story as that of
a moth or butterfly. The form of the adult insect (fig. 1 _a_) is
dominated by the wings--two pairs of scaly wings, carried respectively
on the middle and hindmost of the three segments that make up the
_thorax_ or central region of the insect's body. Each of these three
segments carries a pair of legs. In front of the thorax is the head on
which the pair of long jointed feelers and the pair of large,
sub-globular, compound eyes are the most prominent features. Below the
head, however, may be seen, now coiled up like a watch-spring, now
stretched out to draw the nectar from some scented blossom, the
butterfly's sucking trunk or proboscis, situated between a pair of short
hairy limbs or palps (fig. 2). These palps belong to the appendages of
the hindmost segment of the head, appendages which in insects are
modified to form a hind-lip or _labium_, bounding the mouth cavity below
or behind. The proboscis is made up of the pair of jaw-appendages in
front of the labium, the _maxillae_, as they are called. Behind the
thorax is situated the _abdomen,_ made up of nine or ten recognisable
segments, none of which carry limbs comparable to the walking legs, or
to the jaws which are the modified limbs of the head-segments. The whole
cuticle or outer covering of the body, formed (as is usual in the group
of animals to which insects belong) of a horny (chitinous) secretion of
the skin, is firm and hard, and densely covered with hairy or scaly
outgrowths. Along the sides of the insect are a series of paired
openings or spiracles, leading to a set of air-tubes which ramify
throughout the body and carry oxygen directly to the tissues.
[Illustration: Fig. 2. A. Head of a typical Moth, showing proboscis
formed by flexible maxillae (_g_) between the labial palps (_p_); _c_,
face; _e_, eye; the structure _m_ has been regarded as the vestige of a
mandible. B. Basal part (_b_) of maxilla removed from head, with
vestigial palp (_p_). Magnified.]
Such a butterfly as we have briefly sketched lays an egg on the leaf of
some suitable food-plant, and there is hatched from it the well-known
crawling larva[1] (fig. 1 _b, c, d_) called a caterpillar, offering in
many superficial features a marked contrast to its parent. Except on the
head, whose surface is hard and firm, the caterpillar's cuticle is as a
rule thin and flexible, though it may carry a protective armature of
closely set hairs, or strong sharp spines. The feelers (fig. 3 _At_) are
very short and the eyes are small and simple. In connection with the
mouth, there are present in front of the maxillae a pair of _mandibles_
(fig. 3 _Mn_), strong jaws, adapted for biting solid food, which are
absent from the adult butterfly, though well developed in cockroaches,
dragon-flies, beetles, and many other insects. The three pairs of legs
on the segments of the thorax are relatively short, and as many as five
segments of the abdomen may carry short cylindrical limbs or pro-legs,
which assist the clinging habits and worm-like locomotion of the
caterpillar. No trace of wings is visible externally. The caterpillar,
therefore, differs markedly from its parent in its outward structure, in
its mode of progression, and in its manner of feeding; for while the
butterfly sucks nectar or other liquid food, the caterpillar bites up
and devours solid vegetable substances, such as the leaves of herbs or
trees. It is well-known that between the close of its larval life and
its attainment of perfection as a butterfly, the insect spends a
period as a _pupa_ (fig. 1 _e_) unable to move from place to place, and
taking no food.
[1] The term _larva_ is applied to any young animal which differs
markedly from its parent.
[Illustration: Fig. 3. Head of Caterpillar of Goat-moth (_Cossus_) seen
from behind. _At_, feeler; _Mn_, mandible; _Mx_, maxilla; _Lm_, labium,
spinneret projecting beyond it. Magnified. After Lyonet from Miall and
Denny's _Cockroach_.]
Such, in brief, is the course of the most familiar of insect
life-stories. For the student of the animal world as a whole, this
familiar transformation raises some startling problems, which have been
suggestively treated by F. Brauer (1869), L.C. Miall (1895), J. Lubbock
(1874), R. Heymons (1907), P. Deegener (1909) and other writers[2]. To
appreciate these problems is the first step towards learning the true
meaning of the transformation.
[2] The dates in brackets after authors' names will facilitate reference
to the Bibliography (pp. 124-8).
The butterfly's egg is absolutely and relatively of large size, and
contains a considerable amount of yolk. As a rule we find that young
animals hatched from such eggs resemble their parents rather closely and
pass through no marked changes during their lives. A chicken, a
crocodile, a dogfish, a cuttlefish, and a spider afford well-known
examples of this rule. Land-animals, generally, produce young which are
miniature copies of themselves, for example horses, dogs, and other
mammals, snails and slugs, scorpions and earthworms. On the other hand,
metamorphosis among animals is associated with eggs of small size, with
aquatic habit, and with relatively low zoological rank. The young of a
starfish, for example, has hardly a character in common with its parent,
while a marine segmented worm and an oyster, unlike enough when adult,
develop from closely similar larval forms. If we take a class of
animals, the Crustacea, nearly allied to insects, we find that its more
lowly members, such as 'water-fleas' and barnacles, pass through far
more striking changes than its higher groups, such as lobsters and
woodlice. But among the Insects, a class of predominantly terrestrial
and aerial creatures producing large eggs, the highest groups undergo,
as we shall see, the most profound changes. The life-story of the
butterfly, then, well-known as it may be, furnishes a puzzling exception
to some wide-reaching generalisations concerning animal development. And
the student of science often finds that an exception to some rule is the
key to a problem of the highest interest.
During many centuries naturalists have bent their energies to explain
the difficulties presented by insect transformations. Aristotle, the
first serious student of organised beings whose writings have been
preserved for us, and William Harvey, the famous demonstrator of the
mammalian blood circulation two thousand years later, agreed in
regarding the pupa as a second egg. The egg laid by a butterfly had not,
according to Harvey, enough store of food to provide for the building-up
of a complex organism like the parent; only the imperfect larva could be
produced from it. The larva was regarded as feeding voraciously for the
purpose of acquiring a large store of nutritive material, after which it
was believed to revert to the state of a second but far larger egg, the
pupa, from which the winged insect could take origin. Others again,
following de Réaumur (1734), have speculated whether the development of
pupa within larva, and of winged insect within pupa might not be
explained as abnormal births. But a comparison of the transformation of
butterflies with simpler insect life-stories will convince the enquirer
that no such heroic theories as these are necessary. It will be realised
that even the most profound transformation among insects can be
explained as a special case of growth.