Part 39

Although a very large proportion of the insect inhabitants of any 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.