[55] See Latr. _Familles Naturelles du Règne Animal_, 429.
[56] Collet, in _Month. Mag._ xxxii. 320.
[57] Roesel I. iv. 170.
[58] _Phytologia_, 518.
[59] _Fn. Suec._ 567, 1383.
[60] Amoreux, 276.
[61] Rai. _Cat. Cant._ 45. _Hist. Ins._ 341.
[62] _Comment. in Dioscor._ I. 1. c. 23. 214. Lesser. _L._ ii. 280.
[63] De Geer, iv. 275-6.
[64] Detharding _de Insectis Coleopteris Danicis_, 9.
[65] Reaum. ii. 289. This insect and its caterpillar is finely figured
in Mr. Curtis's elegant and scientific _British Entomology_, t. 147.
[66] _Faun. Suec._ 822.
[67] _Nat. Hist. of Barbad._ 85.
[68] Quoted in Mouffet, 107.
[69] Reaum. i. 667.
[70] Reaum. vi. 99-100. Kirby _Mon. Ap. Ang._ i. 157-8.
[71] Southey's _Madoc_, 4to, Notes, 519.
[72] Haworth _Lepid. Brit._ 44. 57.
[73]
Oft have I smiled the happy pride to see
Of humble tradesmen in their evening glee,
When of some pleasing fancied good possest,
Each grew alert, was busy and was blest:
Whether the call-bird yield the hour's delight,
Or magnified in microscope the mite;
Or whether tumblers, croppers, carriers seize
The gentle mind; they rule it and they please.
There is my friend the weaver; strong desires
Reign in his breast; 'tis beauty he admires:
See to the shady grove he wings his way,
And feels in hope the rapture of the day--
Eager he looks, and soon to glad his eyes,
From the sweet bower by nature form'd arise
Bright troops of virgin moths, and fresh born butterflies.
* * * * *
He fears no bailiff's wrath, no baron's blame,
His is untax'd and undisputed game.
Crabbe's _Borough_, p. 110.
[74] _Linn. Trans._ ii. 315.
[75] Letter to Dr. Wharton. Mason's _Life of Gray_, p. 28.
[76] Illig. _Mag._ ii. 33. iv. 3.
[77] Andrews's _Anecdotes_, 152.
[78] Swartz in _Kongl. Vet. Ac. Nya. band._ ix. 40. PLATE XXIII. FIG.
10.
[79] Young's _Annals of Agriculture_, xi. 406.
[80] No one knew Reaumur's _Abeille Tapissiere_ until Latreille,
happily combining system with attention to the economy of insects,
proved it to be a new species--his _Megachile Papaveris_.--_Hist. de
Fourmis_, 297.
[81] _Bibliothek._ vii. 310.
[82] _Tour on the Continent_, iii. 150.
[83] Shakespear's intention however in this passage was evidently
not, as is often supposed, to excite compassion for the insect, but
to prove that
The sense of Death is most in apprehension,
the actual pang being trifling. _Measure for Measure_, Act iii. Scene 1.
[84] Dr. Smith's _Tour_, i. 162. _Journ. de Phys._ xxv. 336.
LETTER III.
_METAMORPHOSES OF INSECTS._
Were a naturalist to announce to the world the discovery of an animal
which for the first five years of its life existed in the form of a
serpent; which then penetrating into the earth, and weaving a shroud
of pure silk of the finest texture, contracted itself within this
covering into a body without external mouth or limbs, and resembling
more than any thing else an Egyptian mummy; and which, lastly, after
remaining in this state without food and without motion for three
years longer, should at the end of that period burst its silken
cerements, struggle through its earthy covering, and start into day a
winged bird,--what think you would be the sensation excited by this
strange piece of intelligence? After the first doubts of its truth
were dispelled, what astonishment would succeed! Amongst the learned,
what surmises!--what investigations! Amongst the vulgar, what eager
curiosity and amazement! All would be interested in the history of
such an unheard-of phenomenon; even the most torpid would flock to
the sight of such a prodigy.
But you ask, "To what do all these improbable suppositions tend?"
Simply to rouse your attention to the _metamorphoses_ of the insect
world, almost as strange and surprising, to which I am now about to
direct your view,--miracles, which, though scarcely surpassed in
singularity by all that poets have feigned, and though actually
wrought every day beneath our eyes, are, because of their commonness,
and the minuteness of the objects, unheeded alike by the ignorant and
the learned.
That butterfly which amuses you with its aërial excursions, one while
extracting nectar from the tube of the honeysuckle, and then, the
very image of fickleness, flying to a rose as if to contrast the hue
of its wings with that of the flower on which it reposes--did not
come into the world as you now behold it. At its first exclusion from
the egg, and for some months of its existence afterwards, it was a
worm-like caterpillar, crawling upon sixteen short legs, greedily
devouring leaves with two jaws, and seeing by means of twelve eyes so
minute as to be nearly imperceptible without the aid of a microscope.
You now view it furnished with wings capable of rapid and extensive
flights: of its sixteen feet ten have disappeared, and the remaining
six are in most respects wholly unlike those to which they have
succeeded; its jaws have vanished, and are replaced by a curled-up
proboscis suited only for sipping liquid sweets; the form of its head
is entirely changed,--two long horns project from its upper surface;
and, instead of twelve invisible eyes, you behold two, very large,
and composed of at least twenty thousand convex lenses, each supposed
to be a distinct and effective eye!
Were you to push your examination further, and by dissection to
compare the internal conformation of the caterpillar with that of the
butterfly, you would witness changes even more extraordinary. In the
former you would find some thousands of muscles, which in the latter
are replaced by others of a form and structure entirely different.
Nearly the whole body of the caterpillar is occupied by a capacious
stomach. In the butterfly this has become converted into an almost
imperceptible thread-like viscus; and the abdomen is now filled by
two large packets of eggs, or other organs not visible in the first
state. In the former, two spirally-convoluted tubes were filled with
a silky gum; in the latter, both tubes and silk have almost totally
vanished; and changes equally great have taken place in the economy
and structure of the nerves and other organs.
What a surprising transformation! Nor was this all. The change from
one form to the other was not direct. An intermediate state not
less singular intervened. After casting its skin even to its very
jaws several times, and attaining its full growth, the caterpillar
attached itself to a leaf by a silken girth. Its body greatly
contracted: its skin once more split asunder, and disclosed an
oviform mass, without exterior mouth, eyes, or limbs, and exhibiting
no other symptom of life than a slight motion when touched. In this
state of death-like torpor, and without tasting food, the insect
existed for several months, until at length the tomb burst, and out
of a case not more than an inch long, and a quarter of an inch in
diameter, proceeded the butterfly before you, which covers a surface
of nearly four inches square.
Almost every insect which you see has undergone a transformation as
singular and surprising, though varied in many of its circumstances.
That active little fly, now an unbidden guest at your table[85],
whose delicate palate selects your choicest viands, one while
extending his proboscis to the margin of a drop of wine, and then
gaily flying to take a more solid repast from a pear or a peach; now
gamboling with his comrades in the air, now gracefully currying his
furled wings with his taper feet,--was but the other day a disgusting
grub, without wings, without legs, without eyes, wallowing, well
pleased, in the midst of a mass of excrement.
The "grey-coated gnat," whose humming salutation, while she makes
her airy circles about your bed, gives terrific warning of the
sanguinary operation in which she is ready to engage, was a few
hours ago the inhabitant of a stagnant pool, more in shape like a
fish than an insect. Then to have been taken out of the water would
have been speedily fatal; now it could as little exist in any other
element than air. Then it breathed through its tail; now through
openings in its sides. Its shapeless head, in that period of its
existence, is now exchanged for one adorned with elegantly tufted
antennæ, and furnished, instead of jaws, with an apparatus more
artfully constructed than the cupping-glasses of the phlebotomist--an
apparatus which, at the same time that it strikes in the lancets,
composes a tube for pumping up the flowing blood.
The "shard-born beetle," whose "sullen horn," as he directs his
"droning flight" close past your ears in your evening walk, calling
up in poetic association the lines in which he has been alluded to by
Shakespear, Collins, and Gray, was not in his infancy an inhabitant of
air; the first period of his life being spent in gloomy solitude, as
a grub, under the surface of the earth.--The shapeless maggot, which
you scarcely fail to meet with in some one of every handful of nuts
you crack, would not always have grovelled in that humble state. If
your unlucky intrusion upon its vaulted dwelling had not left it to
perish in the wide world, it would have continued to reside there until
its full growth had been attained. Then it would have gnawed itself
an opening, and having entered the earth, and passed a few months in
a state of inaction, would at length have emerged an elegant beetle
furnished with a slender and very long ebony beak: two wings, and
two wing-cases, ornamented with yellow bands; six feet; and in every
respect unlike the worm from which it proceeded.
That bee--but it is needless to multiply instances. A sufficient number
has been adduced to show, that the apparently extravagant supposition
with which I set out may be paralleled in the insect world; and that
the metamorphoses of its inhabitants are scarcely less astonishing than
would be the transformation of a serpent into an eagle.
These changes I do not purpose explaining minutely in this place: they
will be adverted to more fully in subsequent letters. Here I mean
merely to give you such a general view of the subject as shall impress
you with its claims to attention, and such an explanation of the states
through which insects pass, and of the different terms made use of to
designate them in each, as shall enable you to comprehend the frequent
allusions which must be made to them in our future correspondence.
The states through which insects pass are four: the _egg_; the
_larva_; the _pupa_; and the _imago_.
The first of these need not be here adverted to. In the _second_, or
immediately after the exclusion from the egg, they are soft, without
wings, and in shape usually somewhat like worms. This Linné called
the _larva_ state, and an insect when in it a _larva_, adopting
a Latin word signifying a _mask_, because he considered the real
insect while under this form to be as it were masked. In the English
language we have no common term that applies to the second state of
all insects, though we have several for that of different tribes.
Thus we call the coloured and often hairy larvæ of butterflies and
moths _caterpillars_; the white and more compact larvæ of flies, many
beetles, &c. _grubs_ or _maggots_[86]; and the depressed larvæ of
many other insects _worms_. The two former terms I shall sometimes
use in a similar sense, rejecting the last, which ought to be
confined to true _vermes_; but I shall more commonly adopt Linné's
term, and call insects in their second state, _larvæ_[87].
In this period of their life, during which they eat voraciously and
cast their skin several times, insects live a shorter or longer
period, some only a few days or weeks, others several months or
years. They then cease eating; fix themselves in a secure place;
their skin separates once more and discloses an oblong body, and they
have now attained the _third_ state of their existence.
From the swathed appearance of most insects in this state, in which
they do not badly resemble in miniature a child trussed up like a
mummy in swaddling clothes, according to the barbarous fashion once
prevalent here, and still retained in many parts of the continent;
Linné has called it the _pupa_ state, and an insect when under this
form a _pupa_;--terms which will be here adopted in the same sense.
In this state, most insects eat no food; are incapable of locomotion;
and if opened seem filled with a watery fluid, in which no distinct
organs can be traced. Externally, however, the shape of the pupæ of
different tribes varies considerably, and different names have been
applied to them.
Those of the beetle and bee tribes are covered with a membranous
skin, inclosing in separate and distinct sheaths the external organs,
as the antennæ, legs, and wings, which are consequently not closely
applied to the body, but have their form for the most part clearly
distinguishable. To these Aristotle originally gave the name of
_nymphæ_[88], which was continued by Swammerdam and other authors
prior to Linné, who calls them _incomplete_ pupæ, and has been
adopted by many English writers on insects[89].
Butterflies, moths, and some of the two-winged tribe, are in their
pupa state also inclosed in a similar membranous envelope; but their
legs, antennæ, and wings, are closely folded over the breast and
sides; and the whole body inclosed in a common case or covering of a
more horny consistence, which admits a much less distinct view of the
organs beneath it. As these pupæ are often tinged of a golden colour,
they were called from this circumstance _chrysalides_ by the Greeks,
and _aureliæ_ by the Romans, both which terms are in some measure
become anglicized; and though not strictly applicable to ungilded
pupæ, are now often given to those of all lepidopterous insects[90].
These by Linné are denominated _obtected_ pupæ[91].
I have said that _most_ insects eat no food in the pupa state. This
qualification is necessary, because in the metamorphoses of insects,
as in all her other operations, nature proceeds by measured steps,
and a very considerable number (the tribe of locusts, cockroaches,
bugs, spiders, &c.) not only greatly resemble the perfect insect in
form, but are equally capable with it of eating and moving. As these
insects, however, cast their skins at stated periods, and undergo
changes, though slight, in their external and internal conformation,
they are regarded also as being subject to metamorphoses. These pupæ
may be subdivided into two classes: first, those comprised, with some
exceptions, under the Linnean _Aptera_, which in almost every respect
resemble the perfect insect, and were called by Linné _complete_ pupæ;
and secondly, those of the Linnean order _Hemiptera_, which resemble
the perfect insect, except in having only the rudiments of wings, and
to which the name of _semi-complete_ pupæ was applied by Linné, and
that of semi-nymphs by some other authors[92]. There is still a fifth
kind of pupæ, which are not, as in other instances, excluded from the
skin of the larva, but remain concealed under it, and were hence called
by Linné _coarctate_ pupæ. These, which are peculiar to flies and some
other dipterous genera, may be termed _cased-nymphs_[93].
When, therefore, we employ the term _pupa_, we may refer
indifferently to the third state of any insect, the particular order
being indicated by the context, or an explanatory epithet. The terms
_chrysalis_, (dropping _aurelia_, which is superfluous,) _nymph_,
_semi-nymph_, and _cased-nymph_, on the other hand definitely
pointing out the particular sort of pupa meant: just as in Botany,
the common term _pericarp_ applies to all seed-vessels, the several
kinds being designated by the names of capsule, silicle, &c.
The envelope of _cased-nymphs_, which is formed of the skin of the
larva, considerably altered in form and texture, may be conveniently
called the _puparium_[94]: but to the artificial coverings of
different kinds, whether of silk, wood, or earth, &c. which many
insects of the other orders fabricate for themselves previously to
assuming the pupa state, and which have been called by different
writers, _pods_, _cods_, _husks_, and _beans_, I shall continue the
more definite French term _cocon_, anglicized into _cocoon_[95].
After remaining a shorter or longer period, some species only a few
hours, others months, others one or more years, in the pupa state,
the inclosed insect, now become mature in all its parts, bursts the
case which inclosed it, quits the pupa, and enters upon the fourth
and last state.
We now see it (unless it be an apterous species) furnished with
wings, capable of propagation, and often under a form altogether
different from those which it has previously borne--a perfect beetle,
butterfly, or other insect. This Linné termed the _imago_ state,
and the animal that had attained to it the _imago_; because, having
laid aside its _mask_, and cast off its _swaddling bands_, being no
longer disguised or confined, or in any respect imperfect, it is now
become a true representative or _image_ of its species. This state
is in general referred to when an insect is spoken of without the
restricting terms larva or pupa.
Such being the singularity of the transformations of insects, you
will not think the ancients were so wholly unprovided with a show of
argument as we are accustomed to consider them, for their belief in
the possibility of many of the marvellous metamorphoses which their
poets recount. Utterly ignorant as they were of modern physiological
discoveries, the conversion of a caterpillar into a butterfly, must
have been a fact sufficient to put to a nonplus all the sceptical
oppugners of such transformations. And however we may smile in this
enlightened age at the inference drawn not two centuries ago by Sir
Theodore Mayerne, the editor of Mouffet's work on insects, "that if
animals are transmuted so may metals[96]," it was not, in fact, with
his limited knowledge on these subjects, so very preposterous. It
is even possible that some of the wonderful tales of the ancients
were grafted on the changes which they observed to take place in
insects. The death and revivification of the phœnix, from the ashes
of which, before attaining its perfect state, arose first a _worm_
(σκωληξ), in many of its particulars resembles what occurs in the
metamorphoses of insects. Nor is it very unlikely that the doctrine
of the metempsychosis took its rise from the same source. What
argument would be thought by those who maintained this doctrine more
plausible in favour of the transmigration of souls, than the seeming
revivification of the dead _chrysalis_? What more probable, than that
its apparent reassumption of life should be owing to its receiving
for tenant the soul of some criminal doomed to animate an insect of
similar habits with those which had defiled his human tenement[97]?
At the present day, however, the transformations of insects have
lost that excess of the marvellous, which might once have furnished
arguments for the fictions of the ancients, and the dreams of
Paracelsus. We call them metamorphoses and transformations, because
these terms are in common use, and are more expressive of the sudden
changes that ensue than any new ones. But, strictly, they ought
rather to be termed a series of developments. A caterpillar is not,
in fact, a simple but a compound animal, containing within it the
germ of the future butterfly, inclosed in what will be the case of
the pupa, which is itself included in the three or more skins, one
over the other, that will successively cover the larva. As this
increases in size these parts expand, present themselves, and are
in turn thrown off, until at length the perfect insect, which had
been concealed in this succession of masks, is displayed in its
genuine form. That this is the proper explanation of the phenomenon
has been satisfactorily proved by Swammerdam, Malpighi, and other
anatomists. The first-mentioned illustrious naturalist discovered,
by accurate dissections, not only the skins of the larva and of
the pupa incased in each other, but within them the very butterfly
itself, with its organs indeed in an almost fluid state, but still
perfect in all its parts[98]. Of this fact you may convince yourself
without Swammerdam's skill, by plunging into vinegar or spirit of
wine a caterpillar about to assume the pupa state, and letting it
remain there a few days for the purpose of giving consistency to its
parts; or by boiling it in water for a few minutes. A very rough
dissection will then enable you to detect the future butterfly; and
you will find that the wings, rolled up into a sort of cord, are
lodged between the first and second segment of the caterpillar;
that the antennæ and trunk are coiled up in front of the head; and
that the legs, however different their form, are actually sheathed
in its legs. Malpighi discovered the eggs of the future moth, in
the chrysalis of a silkworm only a few days old[99], and Reaumur
those of another moth (_Hypogymna dispar_) even in the caterpillar,
and that seven or eight days before its change into the pupa[100].
A caterpillar, then, may be regarded as a locomotive egg, having
for its embryo the included butterfly, which after a certain
period assimilates to itself the animal substances by which it is
surrounded; has its organs gradually developed; and at length breaks
through the shell which incloses it.
This explanation strips the subject of every thing miraculous, yet by
no means reduces it to a simple or uninteresting operation. Our reason
is confounded at the reflection that a larva, at first not thicker than
a thread, includes its own triple, or sometimes octuple, teguments;
the case of a chrysalis, and a butterfly, all curiously folded in each
other; with an apparatus of vessels for breathing and digesting, of
nerves for sensation, and of muscles for moving; and that these various
forms of existence will undergo their successive evolutions, by aid of
a few leaves received into its stomach. And still less able are we to
comprehend how this organ should at one time be capable of digesting
leaves, at another only honey; how one while a silky fluid should be
secreted, at another none; or how organs at one period essential to the
existence of the insect, should at another be cast off, and the whole
system which supported them vanish.