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[Illustration: NATURE SERIES]
ORIGIN AND METAMORPHOSES OF INSECTS.
[Illustration]
Nature Series
ON THE ORIGIN AND METAMORPHOSES OF INSECTS
BY
Sir John Lubbock, Bart., M.P., F.R.S., D.C.L., LL.D.
Principal of the London Working Men's College; President of the London
Chamber of Commerce; and Vice-Chairman of the London County Council
With Numerous Illustrations
London Macmillan and Co. and New York 1890
The Right of Translation and Reproduction is Reserved
Richard Clay and Sons, Limited, London and Bungay.
First Edition 1873. Reprinted 1874. New Edition 1890.
PREFACE.
For some years, much of my leisure time has been devoted to the study of
the anatomy, development, and habits of the Annulosa, and especially of
Insects, on which subjects I have published various memoirs, chiefly in
the Transactions of the Royal, Linnæan, and Entomological Societies: of
these papers I subjoin a list. Although the details, of which these
memoirs necessarily for the most part consist, offer little interest,
excepting to those persons who are specially devoted to Entomology,
still there are portions which, having reference to the nature of
metamorphoses and to the origin of insects, are of a more general
character. I have also briefly referred to these questions in a
Monograph of the Collembola and Thysanura, recently published by the Ray
Society, and in the Opening Address to the Biological Section of the
British Association at Brighton in 1872. Under these circumstances, it
has been suggested to me that a small volume, containing, at somewhat
greater length, in a more accessible form, and with the advantage of
illustrations, the conclusions to which I have been led on this
interesting subject, might not be altogether without interest to the
general reader. The result, which has already appeared in the pages of
_Nature_, is now submitted to the public, with some additions. I am well
aware that it has no pretence to be in any sense a complete treatise;
that the subject itself is one as to which our knowledge is still very
incomplete, and on which the highest authorities are much divided in
opinion. Whatever differences of opinion, however, there may be as to
the views here put forward, the facts on which they are based will, I
believe, be found correct. On this point I speak with the more
confidence, on account of the valuable assistance I have received from
many friends: to Mr. and Mrs. Busk and Dr. Hooker I am especially
indebted.
The papers above referred to are as follows:--
1. _On Labidocera._--Annals and Magazine of Natural History,
vol. xi., 1853.
2. On Two New Sub-genera of Calanidæ.--Annals and Magazine of
Natural History, vol. xii., 1853.
3. On Two New Species of Calanidæ.--Annals and Magazine of
Natural History, vol. xii., No. lxvii., 1853.
4. On Two New Species of Calanidæ.--Annals and Magazine of
Natural History, vol. xii., No. lxix., 1853.
5. On some Arctic Calanidæ.--Annals and Magazine of Natural
History, 1854.
6. On the Freshwater Entomostraca of South
America.--Transactions of the Entomological Society, vol.
iii., 1855.
7. On some New Entomostraca.--Transactions of the
Entomological Society, vol. iv., 1856.
8. On some Marine Entomostraca found at Weymouth.--Annals and
Magazine of Natural History, vol. xx., 1857.
9. On the Respiration of Insects.--Entomological Annual, 1857.
10. An Account of the Two Methods of Reproduction in
_Daphnia_.--Transactions of the Royal Society, 1857.
11. On the Ova and Pseudova of Insects.--Transactions of the
Royal Society, 1858.
12. On the Arrangement of the Cutaneous Muscles of _Pygæra
Bucephala_.--Linnean Society's Transactions, vol. xxii., 1858.
13. On the Freshwater Entomostraca of South
America.--Entomological Society's Transactions, 1858.
14. On _Coccus Hesperidum_.--Royal Society Proceedings, vol.
ix., 1858.
15. On the Distribution of Tracheæ in Insects.--Linnean
Society's Transactions, vol. xxiii., 1860.
16. On the Generative Organs and on the Formation of the Egg
in Annulosa. Transactions of the Royal Society, 1861.
17. On _Sphærularia Bombi._--Natural History Review, 1861.
18. On some Oceanic Entomostraca.--Linnean Society's
Transactions, vol. xxiii., 1860.
19. On the Thysanura. Part 1.--Linnean Society's Transactions,
1862.
20. On the Development of Lonchoptera.--Entomological
Society's Transactions, 1862.
21. On the Thysanura. Part 2.--Linnean Society's Transactions,
1862.
22. On the Development of Chloëon. Part 1.--Linnean Society's
Transactions, 1863.
23. On Two Aquatic Hymenoptera.--Linnean Society's
Transactions, 1863.
24. On some little-known Species of Freshwater
Entomostraca.--Linnean Society's Transactions, vol. xxiv.,
1863.
25. On _Sphærularia Bombi_.--Natural History Review, 1864.
26. On the Development of Chloëon. Part 2.--Linnean Society's
Transactions, 1865.
27. Metamorphoses of Insects.--Journal of the Royal
Institution, 1866.
28. On _Pauropus_.--Linnean Society's Transactions, 1866.
29. On the Thysanura. Part 3.--Linnean Society's Transactions,
1867.
30. Address to the Entomological Society.--Entomological
Society's Transactions, 1867.
31. On the Larva of Micropeplus Staphilinoides.--Entomological
Society's Transactions, 1868.
32. On the Thysanura. Part 4.--Linnean Society's Transactions,
1869.
33. Addresses to the Entomological Society.--Entomological
Society's Transactions, 1867-1868.
34. On the Origin of Insects.--Journal of the Linnean Society,
vol. xi.
35. Opening Address to the Biological Section of the British
Association.--British Association Report, 1872.
36. Observations on Ants, Bees, and Wasps. Part 1.--Journal of
the Linnean Society, 1873.
37. On British Wild Flowers considered in relation to Insects,
1874.
38. Observations on Ants, Bees, and Wasps. Part 2.--Journal of
the Linnean Society, 1874.
39. Observations on Ants, Bees, and Wasps. Part 3.--Journal of
the Linnean Society, 1875.
40. Observations on Ants, Bees, and Wasps. Part 4.--Journal of
the Linnean Society, 1877.
41. On some Points in the Anatomy of Ants.--Quekett Lecture,
1877.--Microscopical Journal.
42. On the Colors of Caterpillars.--Entomological Society's
Transactions, 1878.
43. Observations on Ants, Bees, and Wasps. Part 5.--Journal of
the Linnean Society, 1878.
44. Observations on Ants, Bees, and Wasps. Part 6.--Journal of
the Linnean Society, 1879.
45. On the Anatomy of Ants.--Linnean Society's Transactions,
1880.
46. Observations on Ants, Bees, and Wasps. Part 7.--Journal of
the Linnean Society, 1880.
47. Observations on Ants, Bees, and Wasps. Part 8.--Journal of
the Linnean Society, 1881.
48. On Fruits and Seeds.--Journal of the Royal Institution,
1881.
49. Observations on Ants, Bees, and Wasps. Part 9.--Journal of
the Linnean Society, 1881.
50. On the Limits of Vision among some of the lower
Animals.--Journal of the Linnean Society, 1881.
51. Observations on Ants, Bees, and Wasps. Part 10.--Journal
of the Linnean Society, 1882.
CONTENTS.
CHAPTER I.
THE CLASSIFICATION OF INSECTS.
Introduction.--Stages in the Life of an Insect.--Classification
of Insects.--Characters derived from the Wings; from the parts
of the Mouth; from the Metamorphoses.--The Classes of Insects:
Hymenoptera, Strepsiptera, Coleoptera, Euplexoptera,
Orthoptera, Thysanoptera, Neuroptera, Trichoptera, Diptera,
Aphaniptera, Heteroptera, Homoptera, Lepidoptera _page_ 1-26
CHAPTER II.
THE INFLUENCE OF EXTERNAL CONDITIONS ON THE FORM AND STRUCTURE
OF LARVÆ.
Larvæ depend partly on the group to which they
belong.--Wood-eating Larvæ.--Larvæ of Lamellicorns.--Larvæ
depend also in part on mode of life.--Larvæ of Hymenoptera, of
_Sirex_; of _Tenthredo_; of Ichneumons; of Bees.--Rudimentary
legs of Bee Embryo.--Beetles, _Weevils_, _Scolytus_,
_Crioceris_, _Sitaris_, Metamorphoses of Pteromalidæ.
_Platygaster_, _Polynema_.--Influence of external
conditions.--Developmental and adaptive Metamorphoses _page_ 27-41
CHAPTER III.
THE NATURE OF METAMORPHOSES.
The life history of an Insect must be considered as a
whole.--Vagueness of the term Larva.--Some larvæ much more
advanced than others.--Organs develope in different order, in
different groups.--Suppressed stages.--Apod condition of
_Phryganea_; of _Aphis_; of
_Chrysopa_.--Libellulidæ.--_Donacia_.--Spiders.--Myriapods.--Apod
stage of Homomorphous Insects once probably longer than
now.--Suppression of embryonic stages.--Metamorphoses of
Hydroida, Crustacea, Isopods, and
Amphipods.--Echinoderms.--Variations in development induced by
the influence of external conditions. _page_ 41-62
CHAPTER IV.
THE ORIGIN OF METAMORPHOSES.
Origin of Metamorphoses.--Views of Messrs. Kirby and
Spence.--Nature of the question.--Young animals often more
similar than mature.--Views of Darwin, Herbert Spencer,
Johannes Müller, Fritz Müller, and Agassiz.--Effect of size of
egg.--Insects leave the egg in a more or less developed
condition.--Consideration of pupal condition.--Quiescence of
pupa.--Period of quiescence at each moult.--Changes not so
abrupt as generally supposed.--Change in
mouth-parts.--Difficulty in reference to Darwinian
theory.--Mouth-parts of _Campodea_ and Collembola, as
intermediate between the mandibulate and haustellate
types.--Change in mouth-parts as connected with pupal
conditions.--Origin of wings.--Use of wings under
water.--Connection of metamorphoses with alternation of
generations.--Parthenogenetic larvæ of _Cecidomyia_.--In
alternation of generations one form always agamic.--Dimorphism
and Dieidism.--Summary and Conclusions _page_ 62-81
CHAPTER V.
THE ORIGIN OF INSECTS.
The Origin of Insects.--Mistaken views of Darwinian
theory.--Natural selection a _vera causa_.--Application of
Darwin's views to Insects.--Similarity of young Crustacea as
compared with mature forms; ditto in Insects.--Type of
Insecta.--Two principal types of larvæ: Hexapod and
Apod.--Conclusions to be drawn from them.--_Campodea_ the modern
representative of the Insect-stock.--_Campodea_, perhaps
derived from Tardigrade.--Vermiform or Apod type of
larva.--Views of Fritz Müller, Brauer, and Packard.--Represents
a still earlier ancestor.--Modern representatives.--_Notommata_,
_Albertia_, _Lindia_.--Earlier forms difficult to trace.--Lowest
forms of animal life.--Yolk-segmentation.--Embryology and
Evolution.--Light thrown by the evolution of the individual on
that of the species _page_ 82-108
DESCRIPTION OF THE PLATES.
PLATE I. p. 7.
FIG.
1. Cricket. Westwood, Intro. to the Modern Classification of
Insects, vol. i. p. 440.
2. Earwig. Westwood, loc. cit. vol. i. p. 399.
3. _Aphis_. Packard, Guide to the Study of Insects, pp. 521, 522.
4. _Scolytus_. Westwood, loc. cit. vol. i. p. 350.
5. _Anthrax_. Westwood, loc. cit. vol. ii. p. 538.
6. _Balaninus_.
7. _Cynips_. Westwood, loc. cit. vol. ii. p. 121.
8. Ant (_Formica_). Westwood, loc. cit. vol. ii. p. 218.
9. Wasp. Ormerod, Nat. Hist. of Wasps, pl. i. fig. 1.
PLATE II. p. 8.
FIG.
1. Larva of Cricket. Westwood, loc. cit. vol. i. p. 440.
2. Larva of _Aphis_. Packard, loc. cit. pp. 521, 522.
3. Larva of Earwig. Westwood, loc. cit. vol. i. p. 399.
4. Larva of _Scolytus_. Westwood, loc. cit. vol. i. p. 350.
5. Larva of _Anthrax_. Westwood, loc. cit. vol. ii. p. 546.
6. Larva of _Balaninus_.
7. Larva of _Cynips_. Westwood, loc. cit. vol. ii. p. 121.
8. Larva of Ant (_Formica_). Westwood, loc. cit. vol. ii. p. 226.
9. Larva of Wasp. Newport, Art. Insecta, Todd's Cycl. Anat. and
Phys., p. 871.
PLATE III. p. 14.
FIG.
1. _Chloëon_. Linn. Trans. 1866.
2. _Meloë_. Spry and Shuckard, Coleoptera Delineated, pl. 56.
3. _Calepteryx_.
4. _Sitaris_. Spry and Shuckard, loc. cit. pl. 56.
5. _Campodea_. Suites à Buffon. Aptéres.
6. _Acilius_. Westwood, loc. cit. vol. i. p. 100.
7. _Termes_. Westwood, loc. cit. vol. ii. p. 12.
8. _Stylops_. Duncan, Met. of Insects, p. 387; Packard, p. 482.
9. _Thrips_. Westwood, loc. cit. vol. ii. p. 1.
PLATE IV. p. 15.
FIG.
1. Larva of _Chloëon_. Linn. Trans. 1863.
2. Larva of _Meloë_. Chapuis and Candèze, Mem. Soc. Roy. Liége,
1853, pp. 1, 7.
3. Larva of _Calepteryx_. Dufour, Ann. Sci. Nat. 1852.
4. Larva of _Sitaris_. Duncan, Met. of Insects, p. 309.
5. Larva of _Campodea_. Gervais' Suites à Buffon. Aptéres.
6. Larva of _Acilius_. Westwood, loc. cit. vol. i. p. 100.
7. Larva of _Termes_. Duncan, loc. cit. p. 348.
8. Larva of _Stylops_. Westwood, Trans. Ent. Soc. 1839, vol. ii.
pl. xv. fig. 13a.
9. Larva of _Thrips_. Westwood, loc. cit. vol. ii. p. i.
PLATE V. p. 99.
FIG.
1-5. _Protamoeba_.
6-9. _Protamyxa aurantiaca_. Haeckel Beit. zur. Monog. der
Moneren, pl. 1.
10-18. _Magosphoera planula_. Haeckel, loc. cit. pl. v.
PLATE VI. p. 105.
FIG.
1-4. Yolk-segmentation in _Laomedea_. After Allman. Mon. of
Tubularian Hydroids. Ray Society.
5-9. Yolk-segmentation in _Filaria_. After Van Beneden. Mem. sur
les Vers Intestinaux.
10-13. Yolk-segmentation in _Echinus_. After Derbès. Ann. des.
Sci. Nat. 1847.
14-17. Yolk-segmentation in _Lacinularia_. After Huxley. J. of
Mic. Sci. 1853.
18-21. Yolk-segmentation in _Purpura_. After Koren and
Danielssen. Ann. des. Sci. Nat. 1853.
22-24. Yolk-segmentation in _Amphioxus_. After Haeckel.
Naturliche Schöpfungsgeschichte, pl. x.
25-29. Yolk-segmentation in Vertebrate. After Allen Thompson.
Art. Ovum. Cyclop. of Anatomy and Physiology.
DESCRIPTION OF THE FIGURES.
FIG. 1. Larva of the Cockchafer (_Melolontha_)
2. Larva of _Cetonia_.
3. Larva of _Trox_.
4. Larva of _Oryctes_.
5. Larva of _Aphodius_.
6. Larva of _Lucanus_.
7. Larva of _Brachytarsus_.
8. Larva of _Crioceris_.
9. Larva of _Sitaris humeralis_.
10. Larva of _Sitaris humeralis_, in the second stage.
11. Larva of _Sitaris humeralis_, in the third stage.
12. Larva of _Sitaris humeralis_, in the fourth stage.
13. Pupa of _Sitaris_.
14. Larva of _Sirex_.
15. Egg of _Rhynchites_, showing the parasitic larva.
16. The parasitic larva, more magnified.
17. Egg of _Platygaster_.
18. Egg of _Platygaster_, showing the central cell.
19. Egg of _Platygaster_, after the division of the central cell.
20. Egg of _Platygaster_, more advanced.
21. Egg of _Platygaster_, more advanced.
22. Egg of _Platygaster_, showing the rudiment of the embryo.
23. Larva of _Platygaster_.--_mo_, mouth; _a_, antenna; _kf_,
hooked feet; _r_, toothed process; _lfg_, lateral
process; _f_, branches of the tail.
24. Larva of another species of _Platygaster_. (The letters
indicate the same parts as in the preceding figure.)
25. Larva of a third species of _Platygaster_. (The letters
indicate the same parts as in the preceding figure.)
26. Larva of _Platygaster_ in the second stage.--_mo_, mouth;
_slkf_, oesophagus; _gsae_, supra-oesophagal ganglion;
_lm_, muscles; _bsm_, nervous system; _gagh_, rudiments
of the reproductive glands.
27. Larva of _Platygaster_ in the third stage.--_mo_, mouth;
_ma_, mandibles; _gsae_, supra-oesophagal ganglion; _slk_,
oesophagus; _ag_, ducts of the salivary glands; _bnm_,
ventral nervous system; _sp_, salivary glands; _msl_,
stomach; _im_, imaginal discs; _tr_, tracheæ; _fk_, fatty
tissue; _ed_, intestine; _ga_, rudiments of reproductive
organs; _ew_, wider portion of intestine; _ao_, posterior
opening.
28. Embryo of _Polynema_.
29. Larva of _Polynema_.--_asch_, rudiments of the antennæ;
_flsch_, of the wings; _bsch_, of the legs; _vfg_,
lateral projections; _gsch_, rudiments of the ovipositor;
_fk_, fatty tissue.
30. Egg of _Phryganea_ (Mystacides).--_A_^1, mandibular segment;
_C_^1-_C_^5, maxillary, labial, and three thoracic
segments; _D_, abdomen.
31. Egg of _Phryganea_ somewhat more advanced.--_b_, mandibles;
_c_, maxillæ; _cfs_, rudiments of the three pairs of
legs.
32. Egg of _Pholcus opilionides_, showing the Protozonites.
33. Embryo of _Julus_.
34. Colony of _Bougainvillea fruticosa_, natural size, attached
to the underside of a piece of floating timber.
35. Portion of the same, more magnified.
36. The Medusa from the same species.
37. Larva of Prawn, Nauplius stage.
38. Larva of Prawn, more advanced, Zoëa stage.
39. Larva of Echino-cidaris oequituberculata seen from above ×6/10.
40. Larva of _Echinus_ × 100.--_A_, front arm; _F_, arms of the
mouth-process; _B_, posterior side arm; _E_^1, accessory
arm of the mouth-process; _a_, mouth; _a_^1, oesophagus;
_b_, stomach; _b_^1, intestine; _o_, posterior orifice;
_d_, ciliated bands; _f_, ciliated epaulets; _c_, disc of
future _Echinus_.
41. _Comatula rosacea_.
42. Larva of _Comatula rosacea_.
43. Larva of _Comatula rosacea_, more advanced.
44. Larva of _Comatula rosacea_, in the Pentacrinus state.
45. Larva of Starfish (Bipinnaria), × 100.
46. Larva of Starfish (Bipinnaria), × 100, seen from the
side.--_a_, mouth; _b_, oesophagus; _c_, stomach; _c_^1,
intestine.
47. Larva of another Bipinnaria, showing the commencement of
the Starfish.--_g_, canal of the ciliated sac; _i_, rudiments
of tentacles; _d_, ciliated band.
48. Larva of Moth (_Agrotis_).
49. Larva of Beetle (_Haltica_).
50. Larva of Saw-fly (_Cimbex_).
51. Larva of _Julus_.
52. _Agrotis suffusa_.
53. _Haltica_.
54. _Cimbex_.
55. _Julus_.
56. Tardigrade.
57. Larva of _Cecidomyia_.
58. _Lindia torulosa_.
59. _Prorhynchus stagnalis_.
60. Egg of Tardigrade.
61. Egg of Tardigrade, after the yolk has subdivided.
62. Egg of Tardigrade, in the next stage.
63. Egg of Tardigrade, more advanced.
ON THE ORIGIN AND METAMORPHOSES OF INSECTS.
CHAPTER I.
_THE CLASSIFICATION OF INSECTS._
About forty years ago the civil and ecclesiastical authorities of St.
Fernando in Chili arrested a certain M. Renous on a charge of
witchcraft, because he kept some caterpillars which turned into
butterflies.[1] This was no doubt an extreme case of ignorance; it is
now almost universally known that the great majority of insects quit the
egg in a state very different from that which they ultimately assume;
and the general statement in works on entomology has been that the life
of an insect may be divided into four periods.
Thus, according to Kirby and Spence,[2] "The states through which
insects pass are four: the _egg_, the _larva_, the _pupa_, and the
_imago_." Burmeister,[3] also, says that, excluding certain very rare
anomalies, "we may observe four distinct periods of existence in every
insect,--namely, those of the egg, the larva, the pupa, and the imago,
or perfect insect." In fact, however, the various groups of insects
differ widely from one another in the metamorphoses they pass through:
in some, as in the grasshoppers and crickets, the changes consist
principally in a gradual increase of size, and in the acquisition of
wings; while others, as for instance the common fly, acquire their full
bulk in a form very different from that which they ultimately assume,
and pass through a period of inaction in which not only is the whole
form of the body altered, not only are legs and wings acquired, but even
the internal organs themselves are almost entirely disintegrated and
re-formed. It will be my object, after having briefly described these
changes, to throw some light on the causes to which they are due, and on
the indications they afford of the stages through which insects have
been evolved.
The following list gives the orders or principal groups into which the
Class Insecta may be divided. I will not, indeed, here enter upon my own
views, but will adopt the system given by Mr. Westwood in his excellent
"Introduction to the Modern Classification of Insects," from which also,
as a standard authority, most of the figures on Plates I. to IV., when
not otherwise acknowledged, have been taken. He divides insects into
thirteen groups, and with reference to eight of them it may be said that
there is little difference of opinion among entomologists. These orders
are by far the most numerous, and I have placed them in capital
letters. As regards the other five there is still much difference of
opinion. It must also be observed that Prof. Westwood omits the
parasitic Anoplura, as well as the Thysanura and Collembola.
ORDERS OF INSECTS ACCORDING TO WESTWOOD.
1. HYMENOPTERA Bees, Wasps, Ants, &c.
2. STREPSIPTERA _Stylops_, _Zenos_, &c.
3. COLEOPTERA Beetles.
4. EUPLEXOPTERA Earwigs.
5. ORTHOPTERA Grasshoppers, Crickets, Cockroaches, &c.
6. THYSANOPTERA _Thrips_.
7. NEUROPTERA _Ephemeras_, &c.
8. TRICHOPTERA _Phryganea_.
9. DIPTERA Flies and Gnats.
10. APHANIPTERA Fleas.
11. HETEROPTERA Bugs.
12. HOMOPTERA _Aphis_, _Coccus_, &c.
13. LEPIDOPTERA Butterflies and Moths.
Of these thirteen orders, the eight which I have placed in capital
letters--namely the first, third, fifth, seventh, ninth, eleventh,
twelfth, and thirteenth, are much the most important in the number and
variety of their species; the other five form comparatively small
groups. The Strepsiptera are minute insects, parasitic on Hymenoptera:
Rossi, by whom they were discovered, regarded them as Hymenopterous;
Lamarck placed them among the Diptera; by others they have been
considered to be most closely allied to the Coleoptera, but they are now
generally treated as an independent order.
The Euplexoptera or Earwigs are only too familiar to most of us. Linnæus
classed them among the Coleoptera, from which, however, they differ in
their transformations. Fabricius, Olivier, and Latreille regarded them
as Orthoptera; but Dr. Leach, on account of the structure of their
wings, considered them as forming the type of a distinct order, in which
view he has been followed by Westwood, Kirby, and many other
entomologists.
The Thysanoptera, consisting of the Linnæan genus _Thrips_, are minute
insects well known to gardeners, differing from the Coleoptera in the
nature of their metamorphoses, in which they resemble the Orthoptera and
Hemiptera. The structure of the wings and mouth-parts, however, are
considered to exclude them from these two orders.
The Trichoptera, or Caddis worms, offer many points of resemblance to
the Neuroptera, while in others they approach more nearly to the
Lepidoptera. According to Westwood, the genus _Phryganea_ "forms the
connecting link between the Neuroptera and Lepidoptera."
The last of these small aberrant orders is that of the Aphaniptera,
constituted for the family Pulicidæ. In their transformations, as in
many other respects, they closely resemble the Diptera. Strauss
Durckheim indeed said that "_la puce est un diptère sans ailes_."
Westwood, however, regards it as constituting a separate order.
As indicated by the names of these orders, the structure of the wings
affords extremely natural and convenient characters by which the various
groups may be distinguished from one another. The mouth-parts also are
very important; and, regarded from this point of view, the Insecta have
been divided into two series--the Mandibulata and Haustellata, or
mandibulate and suctorial groups, between which, as I have elsewhere
shown,[4] the Collembola (_Podura_, _Smynthurus_, &c.) occupy an
intermediate position. These two series are:--
MANDIBULATA.
Hymenoptera.
Strepsiptera.
Coleoptera.
Euplexoptera.
Orthoptera.
Trichoptera?
Thysanoptera?
HAUSTELLATA.
Lepidoptera.
Diptera.
Aphaniptera.
Hemiptera.
Homoptera.
Again--and this is the most important from my present point of
view--insects have sometimes been divided into two other series,
according to the nature of their metamorphoses: "Heteromorpha," to use
the terminology of Prof. Westwood,[5] "or those in which there is no
resemblance between the parent and the offspring; and Homomorpha, or
those in which the larva resembles the imago, except in the absence of
wings. In the former the larva is generally worm-like, of a soft and
fleshy consistence, and furnished with a mouth, and often with six short
legs attached in pairs to the three segments succeeding the head. In the
Homomorpha, including the Orthoptera, Hemiptera, Homoptera, and certain
Neuroptera, the body, legs, and antennæ are nearly similar in their form
to those of the perfect insect, but the wings are wanting."
HETEROMORPHA.
Hymenoptera.
Strepsiptera.
Coleoptera.
Trichoptera.
Diptera.
Aphaniptera.
Lepidoptera.
HOMOMORPHA.
Euplexoptera.
Orthoptera.
Hemiptera.
Homoptera.
Thysanoptera.
Neuroptera.
But though the Homomorphic insects do not pass through such striking
changes of form as the Heteromorphic, and are active throughout life,
still it was until within the last few years generally (though
erroneously) considered, that in them, as in the Heteromorpha, the life
fell into four distinct periods; those of (1) the egg, (2) the larva,
characterized by the absence of wings, (3) the pupa with imperfect
wings, and (4) the imago, or perfect insect.
I have, however, elsewhere[6] shown that there are not, as a matter of
fact, four well-marked stages, and four only, but that in many cases the
process is much more gradual.
The species belonging to the order Hymenoptera are among the most
interesting of insects. To this order belong the gallflies, the
sawflies, the ichneumons, and, above all, the ants and bees. We are
accustomed to class the Anthropoid apes next to man in the scale of
creation, but if we were to judge animals by their works, the chimpanzee
and the gorilla must certainly give place to the bee and the ant. The
larvæ of the sawflies, which live on leaves, and of the Siricidæ or
long-tailed wasps, which feed on wood, are very much like caterpillars,
having three pairs of legs, and in the former case abdominal pro-legs
as well: but in the great majority of Hymenoptera the larvæ are legless,
fleshy grubs (Plate II., Figs. 7-9); and the various modes by which the
females provide for, or secure to, them a sufficient supply of
appropriate nourishment constitutes one of the most interesting pages of
Natural History.
The species of Hymenoptera are very numerous; in this country alone
there are about 3,000 kinds, most of which are very small. In the pupa
state they are inactive, and show distinctly all the limbs of the
perfect insect, encased in distinct sheaths, and folded on the breast.
In the perfect state they are highly organized and very active. The
working ants and some few species are wingless, but the great majority
have four strong membranous wings, a character distinguishing them at
once from the true flies, which have only one pair of wings.
The saw-flies are so called because they possess at the end of the body a
curious organ, corresponding to the sting of a wasp, but which is in the
form of a fine-toothed saw. With this instrument the female sawfly cuts
a slit in the stem or leaf of a plant, into which she introduces her
egg. The larva much resembles a caterpillar, both in form and habits. To
this group belongs the nigger, or black caterpillar of the turnip, which
is often in sufficient numbers to do much mischief. Some species make
galls, but the greater number of galls are formed by insects of another
family, the Cynipidæ.
[Illustration: PLATE I.[7]--MATURE INSECTS.
Fig. 1, Cricket; 2, Earwig; 3, _Aphis_; 4, _Scolytus_; 5, Anthrax;
6, _Balaninus_; 7, _Cynips_; 8, Ant; 9, Wasp.]
[Illustration: PLATE II.--LARVÆ OF THE INSECTS REPRESENTED ON PLATE I.
Fig. 1, Larva of Cricket; 2, Larva of Aphis; 3, Larva of Earwig; 4,
Larva of _Scolytus_ (Beetle); 5, Larva of _Anthrax_ (Fly); 6, Larva of
_Balaninus_ (Nut Weevil); 7, Larva of _Cynips_; 8, Larva of Ant;
9, Larva of Wasp.]
In the Cynipidæ (Plate I., Fig. 7) the female is provided with an organ
corresponding to the saw of the sawfly, but resembling a needle. With
this she stings or punctures the surface of leaves, buds, stalks, or
even roots of various plants. In the wound thus produced she lays one or
more eggs. The effects of this proceeding, and particularly of the
irritating fluid which she injects into the wound, is to produce a
tumour or gall, within which the egg hatches, and on which the larva, a
thick fleshy grub (Plate II., Fig. 7), feeds. In some species each gall
contains a single larva; in others, several live together.
The oak supports several kinds of gallflies: one produces the well-known
oak-apple, one a small swelling on the leaf resembling a currant,
another a gall somewhat like an acorn, another attacks the root; the
species making the bullet-like galls, which are now so common, has only
existed for a few years in this country; the beautiful little spangles
so common in autumn on the under side of oak leaves are the work of
another species, the _Cynus longipennis_. One curious point about this
group is, that in some of the commonest species the females alone are
known, no one yet having ever succeeded in finding a male.
Another great family of the Hymenoptera is that of the ichneumons; the
females lay their eggs either in or on other insects, within the bodies
of which the larvæ live. These larvæ are thick, fleshy, legless grubs,
and feed on the fatty tissues of their hosts, but do not attack the
vital organs. When full-grown, the grubs eat their way through the skin
of the insect, and turn into chrysalides. Almost every kind of insect
is subject to the attacks of these little creatures, which are no doubt
useful in preventing the too great multiplication of insects, and
especially of caterpillars. Some species are so minute that they
actually lay their eggs within those of other insects (Figs. 15, 16).
These parasites assume very curious forms in their larval state.
But of all the Hymenoptera, the group containing the ant, the bee, and
the wasp is the most interesting. This is especially the case with the
social species, though the solitary ones also are extremely remarkable.
The solitary bee or wasp, for instance, forms a cell generally in the
ground, places in it a sufficient amount of food, lays an egg, and
closes the cell. In the case of bees, the food consists of honey; in
that of wasps, the larva requires animal food, and the mother therefore
places a certain number of insects in the cell, each species having its
own special prey, some selecting small caterpillars, some beetles, some
spiders. _Cerceris bupresticida_, as its name denotes, attacks beetles
belonging to the genus _Buprestis_. Now if the Cerceris were to kill the
beetle before placing it in the cell, it would decay, and the young
larva, when hatched, would find only a mass of corruption. On the other
hand, if the beetle were buried uninjured, in its struggles to escape it
would be almost certain to destroy the egg. The wasp has, however, the
instinct of stinging its prey in the centre of the nervous system, thus
depriving it of motion, and let us hope of suffering, but not of life;
consequently, when the young larva leaves the egg, it finds ready a
sufficient store of wholesome food.
Other wasps are social, and, like the bees and ants, dwell together in
communities. They live for one season, dying in autumn, except some of
the females, which hibernate, awake in the spring, and form new
colonies. These, however, do not, under ordinary circumstances, live
through a second winter. One specimen which I kept tame through last
spring and summer, lived until the end of February, but then died. The
larvæ of wasps (Plate II., Fig. 9) are fat, fleshy, legless grubs. When
full-grown they spin for themselves a silken covering, within which they
turn into chrysalides. The oval bodies which are so numerous in ants'
nests, and which are generally called ants' eggs, are really not eggs
but cocoons. Ants are very fond of the honey-dew which is formed by the
Aphides, and have been seen to tap the Aphides with their antennæ, as if
to induce them to emit some of the sweet secretion. There is a species
of _Aphis_ which lives on the roots of grass, and some ants collect these
into their nests, keeping them, in fact, just as we do cows. Moreover
they collect the eggs in the autumn and tend them through the winter
(when they are of no use) with the same care as their own, so as to have
a supply of young Aphides in the spring. This is one of the most
remarkable facts I know in the whole history of animal life. One species
of red ant does no work for itself, but makes slaves of a black kind,
which then do everything for their masters. The slave makers will not
even put food into their own mouths, but would starve in the midst of
plenty, if they had not a slave to feed them. I found, however, that I
could keep them in life and health for months if I gave them a slave for
an hour or two in a week to clean and feed them.
Ants also keep a variety of beetles and other insects in their nests.
That they have some reason for this seems clear, because they readily
attack any unwelcome intruder; but what that reason is, we do not yet
know. If these insects are to be regarded as the domestic animals of the
ants, then we must admit that the ants possess more domestic animals
than we do.
Some indeed of these beetles produce a secretion which is licked by the
ants like the honey-dew; there are others, however, which have not yet
been shown to be of any use to the ants, and yet are rarely, if ever,
found, excepting in ants' nests.
M. Lespès, who regards these insects as true domestic animals, has
recorded[8] some interesting observations on the relations between one
of them (_Claviger Duvalii_) and the ants (_Lasius niger_) with which it
lives. This species of _Claviger_ is never met with except in ants'
nests, though on the other hand there are many communities of _Lasius_
which possess none of these beetles; and M. Lespès found that when he
placed _Clavigers_ in a nest of ants which had none of their own, the
beetles were immediately killed and eaten, the ants themselves being on
the other hand kindly received by other communities of the same species.
He concludes from these observations that some communities of ants are
more advanced in civilization than others; the suggestion is no doubt
ingenious, and the fact curiously resembles the experience of navigators
who have endeavoured to introduce domestic animals among barbarous
tribes; but M. Lespès has not yet, so far as I am aware, published the
details of his observations, without which it is impossible to form a
decided opinion. I have sometimes wondered whether the ants have any
feeling of reverence for these beetles; but the whole subject is as yet
very obscure, and would well repay careful study.
[Illustration: PLATE III.--MATURE INSECTS.
Fig. 1, _Chloëon_; 2, _Meloë_ (after Shuckard); 3, _Calepteryx_;
4, _Sitaris_ (after Shuckard); 5, _Campodea_ (after Gervais);
6, _Acilius_; 7, _Termes_; 8, _Stylops_ (female); 9, _Thrips_.]
[Illustration: PLATE IV. YOUNG FORMS OF THE INSECTS REPRESENTED ON PLATE
III.--Fig. 1, Larva of _Chloëon_; 2, Larva of _Meloë_ (after Chapuis and
Candèze); 3, Larva of _Calepteryx_ (after Léon Dufour); 4, Larva of
_Sitaris_; 5, Larva of _Campodea_; 6, Larva of _Acilius_;
7, Larva of Termes (after Blanchard); 8, Larva of _Stylops_; 9, Larva
of _Thrips_.]
The order Strepsiptera are a small, but very remarkable group of
insects, parasitic on bees and wasps. The larva (Pl. IV., Fig. 8) is
minute, six-legged, and very active; it passes through its
transformations within the body of the bee or wasp. The male and female
are very dissimilar. The males are minute, very active, short-lived, and
excitable, with one pair of large membranous wings. The females (Pl.
III., Fig. 8), on the contrary, are almost motionless, and shaped very
much like a bottle; they never quit the body of the bee, but only thrust
out the top of the bottle between the abdominal rings of the bee.
In the order Coleoptera, the larvæ differ very much in form. The
majority are elongated, active, hexapod, and more or less depressed; but
those of the Weevils (Pl. II., Fig. 6), of _Scolytus_ (Pl. II., Fig. 4),
&c., which are vegetable feeders, and live surrounded by their
food,--as, for instance, in grain, nuts, &c.,--are apod, white, fleshy
grubs, not unlike those of bees and ants. The larvæ of the Longicorns,
which live inside trees, are long, soft, and fleshy, with six short
legs. The Geodephaga, corresponding with the Linnæan genera _Cicindela_
and _Carabus_, have six-legged, slender, carnivorous larvæ; those of
_Cicindela_, which waylay their prey, being less active than the hunting
larvæ of the Carabidæ. The Hydradephaga, or water-beetles (Dyticidæ and
Gyrinidæ), have long and narrow larvæ (Pl. IV., Fig. 6), with strong
sickle-shaped jaws, short antennæ, four palpi, and six small eyes on
each side of the head; they are very voracious. The larvæ of the
Staphylinidæ are by no means unlike the perfect insect, and are found in
similar situations; their jaws are powerful, and their legs moderately
strong. The larvæ of the Lamellicorn beetles (Figs. 1-6)--cockchafers,
stag-beetles, &c.--feed on vegetable substances or on dead animal
matter. They are long, soft, fleshy grubs, with the abdomen somewhat
curved, and generally lie on their side. The larvæ of the Elateridæ,
known as wireworms, are long and slender, with short legs. That of the
glowworm (Lampyridæ) is not unlike the apterous female. The male
glowworm, on the contrary, is very different. It has long, thin, brown
wing-cases, and often flies into rooms at night, attracted by the light,
which it probably mistakes for that of its mate.
The metamorphoses of the Cantharidæ are very remarkable, and will be
described subsequently. The larvæ are active and hexapod. The Phytophaga
(_Crioceris_, _Galeruca_, _Haltica_, _Chrysomela_, &c.) are vegetable
feeders, both as larvæ and in the perfect state. The larvæ are furnished
with legs, and are not unlike the caterpillars of certain Lepidoptera.
The larva of _Coccinella_ (the Ladybird) is somewhat depressed, of an
elongated ovate form, with a small head, and moderately strong legs. It
feeds on Aphides.
Thus, then, we see that there are among the Coleoptera many different
forms of larvæ. Macleay considered that there were five principal types.
1. Carnivorous hexapod larvæ, with an elongated, more or less flattened
body, six eyes on each side of the head, and sharp falciform mandibles
(_Carabus_, _Dyticus_, &c.).
2. Herbivorous hexapod larvæ, with fleshy, cylindrical bodies, somewhat
curved, so that they lie on their side.
3. Apod grub-like larvæ, with scarcely the rudiments of antennæ
(_Curculio_).
4. Hexapod antenniferous larvæ, with a subovate body, the second segment
being somewhat larger than the others (_Chrysomela_, _Coccinella_).
5. Hexapod antenniferous larvæ, of oblong form, somewhat resembling the
former, but with caudal appendages (_Meloë_, _Sitaris_).
The pupa of the Coleoptera is quiescent, and "the parts of the future
beetle are plainly perceivable, being encased in distinct sheaths; the
head is applied against the breast; the antennæ lie along the sides of
the thorax; the elytra and wings are short and folded at the sides of
the body, meeting on the under side of the abdomen; the two anterior
pairs of legs are entirely exposed, but the hind pair are covered by
wing-cases, the extremity of the thigh only appearing beyond the sides
of the body."[9]
In the next three orders--namely, the Orthoptera (grasshoppers, locusts,
crickets, walking-stick insects, cockroaches, &c.), Euplexoptera
(earwigs), and Thysanoptera, a small group of insects well known to
gardeners under the name of _Thrips_ (Pl. I. and II., Figs. 1 and 2)--the
larvæ when they quit the egg already much resemble the mature form,
differing, in fact, principally in the absence of wings, which are more
or less gradually acquired, as the insect increases in size. They are
active throughout life. Those specimens which have rudimentary wings
are, however, usually called pupæ.
The Neuroptera present, perhaps, more differences in the character of
their metamorphoses than any other order of insects. Their larvæ are
generally active, hexapod little creatures, and do not vary from one
another in appearance so much, for instance, as those of the Coleoptera,
but their pupæ differ essentially; some groups, namely, the Psocidæ,
Termitidæ, Libellulidæ, Ephemeridæ, and Perlidæ, remaining active
throughout life, like the Orthoptera; while a second division, including
the Myrmeleonidæ, Hemerobiidæ, Sialidæ, Panorpidæ, Raphidiidæ, and
Mantispidæ, have quiescent pupæ, which, however, in some cases, acquire
more or less power of locomotion shortly before they assume the mature
state; thus that of _Raphidia_, though motionless at first, at length
acquires strength enough to walk, even while still enclosed in the pupa
skin, which is very thin.[10]
One of the most remarkable families belonging to this order is that of
the Termites, or white ants. They abound in the tropics, where they are
a perfect pest, and a serious impediment to human development. Their
colonies are extremely numerous, and they attack woodwork and furniture
of all kinds, generally working from within, so that their presence is
often unsuspected, until it is suddenly found that they have completely
eaten away the interior of some post or table, leaving nothing but a
thin outer shell. Their nests, which are made of earth, are sometimes
ten or twelve feet high, and strong enough to bear a man. One species,
_Termes lucifugus_, is found in the South of France, where it has been
carefully studied by Latreille. He found in these communities five kinds
of individuals--(1) males; (2) females, which grow to a very large size,
their bodies being distended with eggs, of which they sometimes lay as
many as 80,000 in a day; (3) a form described by some observers as Pupæ,
but by others as neuters. These differ very much from the others, having
a long, soft body without wings, but with an immense head, and very
large, strong jaws. These individuals act as soldiers, doing apparently
no work, but keeping watch over the nest and attacking intruders with
great boldness. (4) Apterous, eyeless individuals, somewhat resembling
the winged ones, but with a larger and more rounded head; these
constitute the greater part of the community, and, like the workers of
ants and bees, perform all the labour, building the nest and collecting
food. (5) Latreille mentions another kind of individual which he regards
as the pupa, and which resembles the workers, but has four white
tubercles on the back, where the wings afterwards make their appearance.
There is still, however, much difference of opinion among entomologists,
with reference to the true nature of these different classes of
individuals. M. Lespès, who has recently studied the same species,
describes a second kind of male and a second kind of female, and the
subject, indeed, is one which offers a most promising field for future
study.
Another interesting family of Neuroptera is that of the Ephemeræ, or
Mayflies (Pl. III., Fig. 1), so well known to fishermen. The larvæ (Pl.
IV., Fig. 1) are semi-transparent, active, six-legged little creatures,
which live in water; having at first no gills, they respire through the
general surface of the body. They grow rapidly and change their skin
every few days. After one or two moults they acquire seven pairs of
branchiæ, or gills, which are generally in the form of leaves, one pair
to the segment. When the larvæ are about half grown, the posterior
angles of the two posterior thoracic segments begin to elongate. These
elongations become more and more marked with every change of skin. One
morning, in the month of June, some years ago, I observed a full-grown
larva, which had a glistening appearance, owing to the presence of a
film of air under the skin. I put it under the microscope, and, having
added a drop of water with a pipette, looked through the glass. To my
astonishment, the insect was gone, and an empty skin only remained. I
then caught a second specimen, in a similar condition, and put it under
the microscope, hoping to see it come out. Nor was I disappointed. Very
few moments had elapsed, when I had the satisfaction of seeing the
thorax open along the middle of the back; the two sides turned over; the
insect literally walked out of itself, unfolded its wings, and in an
instant flew up to the window. Several times since, I have had the
pleasure of witnessing this marvellous change, and it is really
wonderful how rapidly it takes place: from the moment when the skin
first cracks, not ten seconds are over before the insect has flown away.
Another family of Neuroptera, the Dragon-flies, or Horse-stingers, as
they are sometimes called, from a mistaken idea that they sting severely
enough to hurt a horse, though in fact they are quite harmless, also
spend their early days in the water. The larvæ are brown, sluggish, ugly
creatures, with six legs. They feed on small water-animals, for which
they wait very patiently, either at the bottom of the water, or on some
aquatic plant. The lower jaws are attached to a long folding rod; and
when any unwary little creature approaches too near the larva, this
apparatus is shot out with such velocity that the prey which comes
within its reach seldom escapes. In their perfect condition, also,
Dragon-flies feed on other insects, and may often be seen hawking round
ponds. The so-called Ant-lions in many respects resemble the
Dragon-flies, but the habits of the larvæ are very dissimilar. They do
not live in the water, but prefer dry places, where they bury themselves
in the loose sand, and seize with their long jaws any small insect which
may pass. The true Ant-lion makes itself a round, shallow pit in loose
ground or sand, and buries itself at the bottom. Any inattentive little
insect which steps over the edge of this pit immediately falls to the
bottom, and is instantaneously seized by the Ant-lion. Should the insect
escape, and attempt to climb up the side of the pit, the Ant-lion is
said to throw sand at it, knocking it down again.
One other family of Neuroptera which I must mention, is the
Hemerobiidæ. The perfect insect is a beautiful, lace-winged, very
delicate, green creature, something like a tender Dragon-fly, and with
bright, green, touching eyes. The female deposits her eggs on leaves,
not directly on the plant itself, but attached to it by a long white
slender footstalk. The larva has six legs and powerful jaws, and makes
itself very useful in destroying the Hop-fly.
The insects forming the order Trichoptera are well known in their larval
condition, under the name of caddis worms. These larvæ are not
altogether unlike caterpillars in form, but they live in water--which is
the case with very few lepidopterous larvæ--and form for themselves
cylindrical cases or tubes, built up of sand, little stones, bits of
stick, leaves, or even shells. They generally feed on vegetable
substances, but will also attack minute freshwater animals. When full
grown, the larva fastens its case to a stone, the stem of a plant, or
some other fixed substance, and closes the two ends with an open grating
of silken threads, so as to admit the free access of water, while
excluding enemies. It then turns into a pupa which bears some
resemblance to the perfect insect, "except that the antennæ, palpi,
wings, and legs are shorter, enclosed in separate sheaths, and arranged
upon the breast." The pupa remains quiet in the tube until nearly ready
to emerge, when it comes to the surface, and in some cases creeps out of
the water. It is not therefore so completely motionless as the pupæ of
Lepidoptera.
The Diptera, or Flies, comprise insects with two wings only, the hinder
pair being represented by minute club-shaped organs called "haltères."
Flies quit the egg generally in the form of fat, fleshy, legless grubs.
They feed principally on decaying animal or vegetable matter, and are no
doubt useful as scavengers. Other species, as the gadflies, deposit
their eggs on the bodies of animals, within which the grubs feed, when
hatched. The mouth is generally furnished with two hooks which serve
instead of jaws. The pupæ of Diptera are of two kinds. In the true
flies, the outer skin of the full-grown larva is not shed, but contracts
and hardens, thus assuming the appearance of an oval brownish shell or
case, within which the insect changes into a chrysalis. The pupæ of the
gnats, on the contrary, have the limbs distinct and enclosed in sheaths.
They are generally inactive, but some of the aquatic species continue to
swim about.
One group of Flies, which is parasitic on horses, sheep, bats, and other
animals, has been called the Pupipara, because it was supposed that they
were not born until they had arrived at the condition of pupæ. They come
into the world in the form of smooth, ovate bodies, much resembling
ordinary dipterous pupæ, but as Leuckart has shown,[11] they are true,
though abnormal, larvæ.
The next order, that of the Aphaniptera, is very small in number,
containing only the different species of Flea. The larva is long,
cylindrical, and legless; the chrysalis is motionless, and the perfect
insect is too well known, at least, as regards its habits, to need any
description.
The Heteroptera, unlike the preceding orders of insects, quit the egg in
a form differing from that of the perfect insect principally in the
absence of wings, which are gradually acquired. In their metamorphoses
they resemble the Orthoptera, and are active through life. The majority
are dull in colour, though some few are very beautiful. The species
constituting this group, though very numerous, are generally small, and
not so familiarly known to us as those of the other large orders, with
indeed one exception, the well-known Bug. This is not, apparently, an
indigenous insect, but seems to have been introduced. The word is indeed
used by old writers, but either as meaning a bugbear, or in a general
sense, and not with reference to this particular insect. In this country
it never acquires wings, but is stated to do so sometimes in warmer
climates. The Heteroptera cannot exactly be said either to sting or
bite. The jaws, of which, as usual among insects, there are two pairs,
are like needles, which are driven into the flesh, and the blood is then
sucked up the lower lip, which has the form of a tube. This peculiar
structure of the mouth prevails throughout the whole order; consequently
their nutriment consists almost entirely of the juices of animals or
plants. The Homoptera agree with the Heteroptera in the structure of the
mouth, and in the metamorphoses. They differ principally in the front
wings, which in Homoptera are membranous throughout, while in the
Heteroptera, the front part is thickened and leathery. As in the
Heteroptera, however, so also in the Homoptera, some species do not
acquire wings. The Cicada, celebrated for its chirp, and the lanthorn
fly, belong to this group. So also does the so-called Cuckoo-spit, so
common in our gardens, which has the curious faculty of secreting round
itself a quantity of frothy fluid which serves to protect it from its
enemies. But the best known insects of this group are the Aphides or
Plant-lice; while the most useful belong to the Coccidæ, or scale
insects, from one species of which we obtain the substance called lac,
so extensively used in the manufacture of sealing-wax and varnish.
Several species also have been used in dyeing, especially the Cochineal
insect of Mexico, a species which lives on the cactus. The male _Coccus_
is a minute, active insect, with four large wings; while the female, on
the contrary, never acquires wings, but is very sluggish, broad, more or
less flattened, and in fact, when full grown, looks like a small brown,
red, or white scale.
The larva of the order Lepidoptera are familiar to us all, under the
name of caterpillars. The insects of this order in their larval
condition are almost all phytophagous, and are very uniform both in
structure and in habits. The body is long and cylindrical, consisting of
thirteen segments; the head is armed with powerful jaws; the three
following segments, the future prothorax, mesothorax, and meta-thorax,
each bears a pair of simple articulated legs. Of the posterior segments,
five also bear false or pro-legs, which are short, unjointed, and
provided with a number of hooklets. A caterpillar leads a dull and
uneventful life; it eats ravenously, and grows rapidly, casting its skin
several times during the process, which generally lasts only a few
weeks; though in some cases, as for instance that of the goat-moth, it
extends over a period of two or three years, after which the larva
changes into a quiescent pupa or chrysalis.