country may be captured in their _perfect_ state by the active
Entomologist, yet there is no small number of them that probably he
may never meet with in that state, and to secure which he must have
recourse to other methods. He can procure _pupæ_ by digging for
them in woods, under trees, &c., as above directed[1576], keeping
them in some of their native earth till they are disclosed; or he
must collect _larvæ_, and _breed_ them; for which I shall now give
you some instructions.--The insects we are particularly concerned
with under this head are the caterpillars of _Lepidoptera_ and of
the saw-flies (_Serrifera_). If, however, in our entomological
rambles we discover the larvæ of insects of _other_ Orders upon
their appropriate food, we may often attempt to breed them with
success: but as you will seldom thus get species that you will not
also meet with in their imago state, and the general directions for
breeding will include almost all, I shall principally consider the
best mode of breeding _caterpillars_, and _pseudo-caterpillars_. The
first thing is to collect them. In beating the trees, bushes, and
plants, while hunting for _Coleoptera_, &c., the Entomologist will
often displace caterpillars, which, if unknown, he should put into
a pill-box with a portion of their food: but _Lepidopterists_ often
sally into the woods, &c., for the express purpose of collecting
these only. When engaged in this employment, the best plan is to
take a sheet with you, and when you mean to beat the branches of any
tree, place it as near them as you can, upon four or more sticks
fastened in the ground, so as to leave the upper surface concave, and
it will receive the falling caterpillars when you beat. If you aim
at the pseudo-caterpillars of the _Cimbicidæ_, you must turn your
attention principally to the different species of sallows and willows
(_Salix_). Your spoils you will put into boxes with their food, as
above directed, to bring them home.
There are several kinds of boxes recommended to receive them and
breed them in. If your only object is to get the perfect insect, a
cubical box of moderate dimensions, glazed in front or on one side
to enable you to watch their proceedings, with the other sides and
top fitted with fine canvass for the admission of air, will very
well answer this purpose; or your box may be canvassed all round,
with a door in front[1577]. In this you may place a small garden-pot
filled with earth, with a phial of water plunged in it to receive the
insects' food. This may be moved, when you wish to change the water,
without disturbing the earth, which should be kept somewhat moist.
The earth is for those caterpillars whose pupæ are subterranean. But
as you will probably wish to proceed scientifically, and ascertain
precisely the moth that comes from each caterpillar, I should
strongly recommend to you a box invented by Mr. Stephens, which he
describes in a letter to me in nearly these words:--"The length of
the box is 20 inches, height 12, and breadth 6; and it is divided
into _five_ compartments. Its lower half is constructed intirely
of wood, and the upper of coarse gauze stretched upon wooden or
wire frames: each compartment has a separate door, and is moreover
furnished with a phial in the centre for the purpose of containing
water, in which the food is kept fresh; and is half-filled with
a mixture of fine earth and the dust from the inside of rotten
trees; the latter article being added for the purpose of rendering
the former less binding upon the pupæ, as well as being highly
important for the use of such larvæ as construct their cocoons of
rotten wood. The chief advantages of a breeding cage of the above
construction are, the occupation of less room than five separate
cages, and a diminution of expense; both important considerations
when any person is engaged extensively in rearing insects. Whatever
be the construction of the box, it is highly necessary that the
larvæ be constantly supplied with fresh food, and that the earth at
the bottom should be kept damp. To accomplish the latter object,
I keep a thick layer of moss upon the surface, which I take out
occasionally (perhaps once a week during hot weather, and once a
fortnight or three weeks in winter), and saturate completely with
water, and return it to its place: this keeps up a sufficient supply
of moisture, without allowing the earth to become too wet, which is
equally injurious to the pupæ with too much aridity. By numbering the
cells, and keeping a register corresponding with the numbers, the
history of any particular larva or brood may be traced."
In attending to your insects in their cells, your expectations will
sometimes be disappointed, when, instead of a butterfly or moth,
you find only an _Ichneumon_. But this you must not regard as _all_
misfortune; for by this means you will be better instructed in the
history of each species, and learn to the attack of what enemies it
is exposed: and thus you may get many species of these parasitic
devourers of insects that you would not elsewhere meet with. If your
caterpillars, however, appear to be of a rare kind, you must watch,
and often examine them; and if you discover black specks upon any
one, that appear unnatural or like nits, they may be extracted, Mr.
Haworth assures us[1578], by a pair of small pliers; and if the
operation is adroitly performed, the caterpillar will recover and do
well. You will often meet Lepidopterous larvæ travelling over roads
and pathways: at such times they have usually done feeding, and are
seeking a spot in which they may assume the pupa with safety. These
you may place in one of your cells, and they will select a station
for themselves. You must be careful frequently to examine the boxes
in which you have pupæ, that you may take the imago as soon as it
appears, and before it has had time to injure itself in attempting to
escape. I mentioned to you on a former occasion Reaumur's experiments
to accelerate the appearance of the butterfly[1579];--there is
another still more remarkable, to which he had recourse for this
purpose: it was by hatching his pupæ under a _hen_!! You will wonder,
perhaps, how this could be effected, and be disposed to maintain
that the pupæ must be crushed by the weight of the brooding animal.
How did the ingenious and illustrious experimentalist prevent this?
He prepared a hollow ball of glass, open at one end, about the
shape and size of a turkey's egg. Having several chrysalises of the
nettle-butterfly (_Vanessa Urticæ_) suspended to a piece of paper,
he cut out some of these singly, with a square portion of the paper
attached to them, and covered with paste the side opposite to that
from which the chrysalis was suspended: these he introduced into the
ball through the aperture, placing them as near to each other as
possible, taking care so to apply the pasted surface to the inside of
the ball, that when the side to which they were fixed was uppermost
they all hung as from a vault. This being done, he stopped the
aperture with a linen plug, but not so completely as to cut off all
communication with the atmosphere: he next placed the egg under a hen
that had been sitting some days, who always kept it at the side of
the nest, where it nevertheless derived benefit from her incubation.
After the first day its interior was covered with vapour transpired
by the chrysalises. Upon this Reaumur took the egg, and removing the
linen plug it soon became dry again: he replaced it under the hen,
and no vapour afterwards appeared. In about _four_ days the first
butterfly ever hatched under a hen made its appearance; it would
probably have required _fourteen_ under ordinary circumstances. He
tried the same experiment with some Dipterous pupæ; but the heat was
too great for them, and they all perished[1580].
* * * * *
Having properly prepared and set your specimens as above directed,
the next step, when they have remained a sufficient time to be
perfectly dry, is to place them in your cabinet. If you collect
_foreign_ insects as well as British, you may either preserve
the latter in a separate cabinet, or keep both in the same,
distinguishing the indigenous species by a particular mark. The
letter B in red ink, if the pin which transfixes the insect be run
through it, or, in the case of _Lepidoptera_, placed before the
specimen, would be a very distinct and sufficient indication of
them. The drawers of your cabinets should be about 18 inches square,
and from the glass to the corked bottom about an inch and a half in
depth: but the larger _Dynastidæ_, as _Megasoma Actæon_, &c., will
require _two_ inches. The frame of the glass should be rabbeted
underneath; and parallel with the sides of the drawer, but a little
lower, there should be inner side-pieces fixed, so as to form a
cavity all round of a proper width to closely receive the rabbet,
and likewise to contain the camphor for preserving your insects from
the attack of mites, &c.; to emit the scent of which, many holes
should be bored in the side-pieces. Each cabinet may contain _forty_
of these drawers in a double series, protected by folding doors; and
you may place one cabinet upon another, if your space admits it. You
will find a tool used by bell-hangers for cutting their wire very
convenient to behead or otherwise curtail the pins, as those with
which foreign insects are transfixed are often too long. If you cut
them off below the insect, cut them obliquely, which will leave a
point that will enter the cork.
When your drawers are _smoothly_ corked[1581] and neatly papered,
first divide each transversely by a _full_ black line; parallel with
this, on each side, draw a line with red ink: then, for arranging
your insects, draw _pencil_ lines, which are easily obliterated, at
right angles with the others, according to the general size of the
insects that are to occupy them. Insects look better thus arranged
in double columns, than if the pencil lines traversed the whole
width of the drawers. In arranging them, you may either place them
in a straight line _between_ the pencil lines,--which I think is
best,--or _upon_ them. You will begin your columns from the red
lines in the middle, and not from the sides of the drawer; thus the
heads of those on one side of it will be in an opposite direction
to those on the other. Where your pins are very fine and weak, you
must make a hole first with a common lace-pin; otherwise, in forcing
them into the cork, they will bend. In labelling your specimens, you
should stick the appellation of the genus or subgenus with a pin
before the species that belong to it. As to the species themselves,
you may either number them 1, 2, 3, &c., sticking the pin they are
upon through the number, and denoting them by a corresponding one
in your catalogue; or you may at once write the trivial name, with
the initial of the genus upon a label transfixed in the same manner.
_Lepidoptera_ cannot easily be arranged in columns. Perhaps if
_squares_, corresponding with the size and number of the specimens
of any given species you wish to preserve, were made with pencil, a
label of the trivial name of the species, or a number being placed
at its head, it would be as good a way as any other. But every one
must be left to his own taste in these matters. Wherever you can,
procure a specimen of each _sex_ of an insect, and where _important_
characters require it, let some of your Lepidopterous specimens
exhibit the _under side_ of the wings.
In arranging insects in your cabinet, if you wish to have it
scientific, as much as the nature of the subject will admit, follow
the series of _affinities_; but you may reserve a few drawers to
place in contrast _analogous_ forms. As your numbers of species
increase you will have to alter your arrangement; but as pencil lines
are easily rubbed out, this will occasion you less trouble than if
they were drawn with ink. You should always be careful under each
genus to leave space for new species.
As certain _Acarina_, _Tineidæ_, _Ptinidæ_, &c., prey upon dead
insects, you will of course wish to know how they may be kept out of
your drawers, or banished when detected there. _Camphor_ is the general
remedy recommended. The cavity closed by the rabbet of the glass frame
affords a good receptacle for this necessary article: put some roughly
powdered into each side, and be careful to renew it when evaporated.
This will generally preserve your insects, as will be seen from the
result of the following experiment.--Some insects in a chip box having
become much infested by mites and _Psocus pulsatorius_, I placed under
a wine-glass several of each along with roughly-powdered camphor: at
the end of twenty-four hours the mites were alive; but at the end of
forty-eight they were all apparently dead, and did not revive upon the
removal of the camphor. The specimens of _Psocus_ all appeared dead in
an hour, and never revived. If the camphor be put only into one side of
a drawer, and in a lump, though perhaps it may keep out mites, &c., it
will not expel them.
I am, &c.
FOOTNOTES:
[1554] _Entomologist's Useful Compendium._ _t._ xi. _f._ 5.
[1555] PLATE XXIV. FIG. 1.
[1556] _Lepidopt. Britann._ 20.
[1557] VOL. I. p. 187.
[1558] PLATE XXIV. FIG. 3.
[1559] PLATE XXIV. FIG. 4.
[1560] Samouelle's _Compendium_. _t._ xi. _f._ 1, 2.
[1561] PLATE XXIV. FIG. 5.
[1562] PLATE XXIV. FIG. 2. N.B. The net is represented too _shallow_
in this figure.
[1563] _Voyage to the Cape._ i. 63. Eng. Trans.
[1564] LETTER II.
[1565] Illig. _Mag._ iii. 222. Mr. Stephens however, whose experience
is great in the best modes of collecting, is of opinion that insects
that have been immersed in spirits of wine are apt to become mouldy.
We have not ourselves observed this.
[1566] PLATE XXIV. FIG. 7. _c._
[1567] Ibid. _a, b._
[1568] Ibid. _b._
[1569] Ibid. _a._
[1570] PLATE XXIV. FIG. 8.
[1571] In the figure just quoted the artist has represented the
insect as transfixed in this way.
[1572] PLATE XXIV. FIG. 9.
[1573] Mr. Samouelle (_Useful Compendium_, 321) recommends a somewhat
different method.
[1574] VOL. III. p. 623--.
[1575] Some other methods are recommended by Mr. Samouelle, which the
reader will find in his _Useful Compendium_, 318.
[1576] See above, p. 529.
[1577] PLATE XXIV. FIG. 6.
[1578] _Lepidopt. Britann._ 87.
[1579] VOL. III. p. 262--.
[1580] Reaumur ii. 12--.
[1581] See Mr. Samouelle's _Compendium_, 311.
LETTER LI.
_INVESTIGATION OF INSECTS._
An entomologist who aspires to more than the character of a mere
amateur, will not be content with filling his cabinet with nameless
objects for the sole amusement of the eye; but will also be anxious
to acquire some knowledge of what he has collected, and to ascertain
by what _names_, whether indicating their genus or species, they have
been distinguished by scientific writers who have described insects
either in general or those of particular districts. Thus only can he
himself derive profit from any discoveries he may make, or contribute
to the further progress of the science[1582].
But in order to accomplish this object effectually, you must remember
and practise the _Onslow_ motto--_Festina lente_:--you must not be
too eager to name your _species_, but begin first with _grouping_
your collection. The only way to acquire, in any degree, a correct
knowledge of the Natural System, or of the general plan of the
CREATOR, which is the _primum_ and _ultimum_ of true science, is by
studying _groups_. The knowledge of species is indeed indispensable
for the registry of facts and other practical purposes, but the
knowledge of groups leads to a higher wisdom; and indeed it is
through these that we best descend to the study of species.
I will suppose you have made yourself master of so much of the
technical language, particularly the names and most important
attributes of the principal organs of insects, as will suffice for
understanding descriptions, or knowing these parts when you see them.
I will also further suppose that what was formerly said on these
subjects has been sufficiently studied, to enable you without much
difficulty or hesitation to say whether any given object belongs to
the Class _Insecta_ or _Arachnida_, or to which of their respective
Orders[1583]. You are therefore qualified to arrange your collection
into its _primary_ groups. But you have seen that many _others_
intervene between the Order and the genus or species. As the _genera_
of Linné are mostly primary groups of Orders, perhaps, setting aside
such insects included in them by him as your eye and their apparent
characters convince you have no claim to a place there, your next best
step would be to make yourself thoroughly acquainted with them. When
you have accurately marshalled and intimately studied these groups,
you will probably have acquired an eye and a tact, _experto crede_,
for grouping without book, and may proceed by analysis to resolve your
whole collection, as nearly as possible, into as many as nature seems
to indicate to you. In doing this you will doubtless at first fall
into many errors; but these, practice and a closer examination will
in time enable you to rectify. Having thus got your groups as near
to nature as you can, you may now have recourse to those authors,
particularly Fabricius and Latreille, who have subdivided the genera
of Linné; and you will see which of your groups agree with theirs,
detect your own errors, and often theirs, and be enabled to label each
of your genera and higher groups, if already known, with its modern
appellation. You are now qualified also to enter scientifically into
the study of the _characters_ that distinguish groups, and may proceed,
wherever opportunity is afforded, to examine the _trophi_, which may
often be displayed sufficiently by the means recommended in my last
letter[1584]. In this way you may learn also to know your groups as
well by character as by habit, and be qualified to trace the gradual
progress of nature from form to form; and may look upon yourself as
duly prepared to put the last hand to your labours, and proceed to the
examination of _species_.
It will have occurred to you, in making out your genera or _lowest_
groups, that some consist of a vastly greater number of species than
others. It seems advisable therefore, when you apply yourself seriously
to ascertain what described ones your cabinet contains, to begin with
those genera which appear to be poor in them; for here your labour
will be comparatively light, from the small number you will have to
examine; and you will become practised in the employment before you
are called upon to attack those that overflow. Had Fabricius and other
describers of species taken the trouble to subdivide the larger groups,
as might easily have been done, into more _genera_ and _subgenera_,
the student would have been spared a most discouraging labour. To be
obliged to compare a single individual with the descriptions of from
100 to 300 species[1585], to ascertain its name, seems enough to make
you start aside with horror from the employment, and be content that
your species should remain unnamed, rather than expose yourself to such
a waste of time and patience. But to lessen your alarm and encourage
you to proceed, I must observe to you, though in a few instances it
may be necessary to advert to the description of every single species
in a section, yet that this is seldom requisite; and where it is,
there are many helps to diminish the labour and abridge the process.
A large number of insects are characterized by their _colour_; and
it is the practice of all good describers to begin their definition
of the species with that which predominates, and then to enumerate
the variations from it. Thus, if an insect be all _black_ except the
_thorax_, _antennæ_, and _legs_, you will find it thus characterized,
"_Black_: _with thorax, antennæ, and legs ferruginous_"; and so on.
Hence, having noticed the predominant colour of your unknown species,
in many genera you may compare it with the descriptions contained in a
whole page at a single glance, and only read the further descriptions
when the colour agrees. A practised Entomologist will thus investigate
his insects with a rapidity which to an unlearned bystander would seem
impossible. Though I have instanced _colour_ as being the character
most commonly employed in describing species of insects, you will
readily conceive that in some tribes other characters afford more
prominent distinctions. Thus in the _Dynastidæ_ and many other
Petalocerous beetles, the principal specific character is derived
from the _horns_ or _tubercles_ that arm the head and thorax: in
_Lucanus_ from the _mandibulæ_; and in _Prionus_ from the marginal
_teeth_ of the thorax. If the insect, then, you want to name belongs
to any of these genera, having observed its peculiar characters in
this respect, you may ascertain in a very few minutes whether any
already described exhibit the same. This facility of investigation can
be better acquired by practice than precept, and cannot be attained
all at once. The above hints, however, may be of some use; and cannot
fail to be so, if you always endeavour to make yourself acquainted by
a previous careful examination with the characters of every new insect
you acquire,--whether those of form, colour, or sculpture,--before you
attempt to discover its name in Fabricius or any other author.
When you have made such proficiency in the study as to be familiar
with a few species of each section of an extensive genus, the labour
of investigation will sometimes be greatly facilitated by attending
to that conformity between the proportions, general aspect, and
figure of a known and an unknown insect, which Naturalists express
by the name of _habit_, and which, though easily perceived by
a practised eye, is described with such difficulty. Scientific
Entomologists in their descriptions have usually taken care to place
near to each other, species agreeing in habit. When therefore you
know the name of one species, and find another of the same general
habit, you may commonly take it for granted that if described at all
by your author, it will be placed near that already known to you.
Thus, supposing you are acquainted with that common weevil _Cionus
Scrophulariæ_, and find its near relation _C. Blattariæ_; instead
of comparing it one by one with the 161 species which compose the
_Longirostres femoribus dentatis_ of the Fabrician genus _Rhynchænus_
in the _Systema Eleutheratorum_, you would at once turn to the
former, very near which you would without further trouble discover
it. Fortunate, would it be, could the Entomologist always depend on
thus finding descriptions of allied species in the neighbourhood
of each other; but unhappily the most distinguished authors have
sometimes violated this important rule, so that we cannot always be
certain that any given species is not elsewhere described than in
its right place. Fabricius in many instances often removes widely
asunder insects not merely related, but which are in reality scarcely
more than varieties of the same species[1586]. In fact, the attention
of this celebrated author was so distracted by the immensity of the
materials he had to arrange, by the distance of the cabinets, in many
cases, from each other, the new species of which he undertook to
describe, and the rapidity with which they necessarily passed under
his eye, that he seems never to have attained any nice perception of
the _affinities_ of insects.
You must not conclude, however, that the investigation of a new
insect is even to an adept always a work of ease and dispatch.
Often, when seemingly ascertained by the rapid process above
indicated, a further inquiry will be requisite; the more detailed
description must be read, and figures consulted, before its name can
be indisputably determined. In addition to the difficulty arising
from the insufficient characters frequently given by Fabricius and
the older authors, obstacles arising from their errors not seldom
intervene. Thus they have sometimes selected for a _specific_
character,--as in the case of _Megachile centuncularis_, _Nomada
ruficornis_, and various other insects,--what really only indicates
a _family_. At other times _sexual_ characters common to many,--as
in _Eucera longicornis_, _Locusta perspicillata_, &c.,--have
been had recourse to. In these cases, in order satisfactorily to
ascertain your species, you must further consult the _synonyms_ and
_habitat_ given by the original describer, especially the figures
he has referred to. When all these fail, as they sometimes will,
the _dernier resort_ is a reference to the cabinet containing the
original specimen from which the description was drawn. British
Entomologists possess an invaluable privilege, which their
continental brethren may well envy them, in having the most liberal
access, indulged to them by the learned President of the Linnean
Society, to Linné's collection of insects, from which a large
proportion of the species he described may be ascertained[1587].
Several of the cabinets, especially the Banksian,--now the property
of the Linnean Society,--from which Fabricius described his insects,
may also still be consulted; and thus many mistakes rectified, which
would otherwise greatly mislead[1588].