Part 19

[484] Ibid. 364. _N. Dict. d'Hist. Nat._ xx. 365. Huber _Fourmis_ 78. M. Huber does not say expressly that the grubs of ants do not change their skin; but his account seems to imply that they change it only previously to their metamorphosis.

[485] Lyonnet 11.

[486] _N. Dict. d'Hist. Nat._ vi. 290.

[487] _De Bombycibus_, 68.

[488] _Opusc._ i. 27.

[489] _Linn. Trans._ x. 399.

[490] _N. Dict. d'Hist. Nat._ vii. 129.

[491] As the larvæ of Ephemeræ usually live in the submerged part of the banks of rivers, perhaps they may be regarded as following the economy of subterranean _terrestrial_ larvæ.

[492] A caterpillar nearly answering to the description of that of _Bombyx camelina_, which I found upon the hazel, after a few days produced sixteen grubs of some _Ichneumon_. At first these grubs were green, but they became gradually paler; and after a day or two became pupæ. But I mention this circumstance here for another reason: upon examining them after this last occurrence, I observed that they adhered to the lid of the box in which I kept the larva, arranged somewhat circularly; and at a little distance from the anus of each was a pea-green mass, consisting of about eight oval granules, which appeared like so many minute eggs. These were the excrement evacuated by each grub previously to its becoming a pupa. The appearance of this little group, with their verdant appendage, formed a curious spectacle: they are still pupæ, July 30, 1822.

[493] Except some species of _Polyammatus_ Latr. (_Thecla_, _Argynnis_ F.), _P. Argiolus_, _Corydon_, &c., and _Hesperia Rubi_, _Betulæ_ F., &c. Some of the larvæ of the former become pupæ within the stalk of some plant, or partly under the earth: those of the latter usually in a leaf to which the abdomen is fastened by various threads. These last are the _rouleuses_ of the butterfly-tribe, living, like some moths, in leaves that they have rolled up. _N. Dict. d'Hist. Nat._ xxiv. 499.

[494] PLATE XXIII. FIG. 1. _a._

[495] PLATE XXIII. FIG. 8. _a._

[496] Bonnet is of opinion that this twirling process is not with any view to get rid of the exuviæ, but is caused only by the irritation occasioned by the spines of the skin of the caterpillar when they touch that of the pupa. _Œuv._ ii. 109.

[497] For the above account see Reaum. i. _Mem._ x. xi.

[498] _N. Dict. d'Hist. Nat._ vi. 291--.

[499] _De Bombyc._ 24.

[500] i. 498.

[501] _De Bombyc._ 43.

[502] _N. Dict. d'Hist. Nat._ vi. 294.

[503] Lesser. L. ii. 150, note 22. Boyle says an English lady found that the silk of a single cocoon would extend 300 English leagues or 900 miles. But this must be a mistake.

[504] Reaum. i. 555--.

[505] PLATE XVII. FIG. 5. _b._

[506] De Geer i. _t._ xxxii. _f._ 3-6.

[507] De Geer i. 463--.

[508] Reaum. ii. _Mem._ xi. Comp. De Geer ii. 162. Reaum. ii. 424.

[509] _B. Catax_--Pupa arcte folliculata. _Fab._

[510] _Travels in Greece_, 285.

[511] See above, VOL. I. p. 476--.

[512] Merian _Surinam._ _t._ xv.

[513] Reaum. ii. _t._ xxiii. _f._ 5.

[514] Sepp. iv. _t._ viii. _f._ 5.

[515] Reaum. i. _t._ xliv. _f._ 2.

[516] PLATE XVII. FIG. 7.

[517] I have a black one from Mr. Francillon's cabinet.

[518] _N. Dict. d'Hist. Nat._ vi. 294.

[519] See above, VOL. II. p. 298--.

[520] Reaum. ii. 436.

[521] Reaum. i. 503.

[522] Peck on _Locust-tree Insects_, 69.

[523] Bonnet ii. 260.

[524] Sepp. iv. _t._ ii. _f._ 4.

[525] Brahm. _Ins. Kal._ 289.

[526] PLATE XVII. FIG. 8.

[527] The thick cocoons of _Attacus Paphia_, _Polyphemus_, &c. are also thus fastened between leaves.

[528] Merian _Europ._ ii. _t._ ix.

[529] Reaum. ii. 284.

[530] Ibid. i. 524.

[531] Bonnet ii. 297.

[532] Ibid. ix. 181.

[533] Reaum. v. 102.

[534] Ibid. iv. 269.

[535] De Geer ii. 1084. Comp. Ray _Hist. Ins._ Præf. xi. It is the opinion of M. P. Huber, that in this case the _naked_ pupæ are deprived of their cocoons by the neuters: he states, indeed, that he has often seen them pulled off by them, and also by those of _F. canicularia_; and he seems to think that these larvæ are never developed. _Mœurs des Fourmis_, 84. note 1.

[536] II. viii. 16.

[537] _Linn. Trans._ vii. _t._ ii. _f._ 5, 6.

[538] _Wien. Verz._ I possess a cocoon of this kind from New Holland, even now quite solid, and retaining its form. No silk appears to have been used in its composition.

[539] Reaum. i. 579.

[540] Ibid. vi. 368.

[541] Ibid. i. 542.

[542] Ibid. 543.

[543] _Linn. Trans._ i. 196.

[544] Reaum. i. 545--.

[545] _Pyral._ 8. 3. _t._ iii. _f._ 16.

[546] See above, VOL. I. p. 172--.

[547] Reaum. ii. 491.

[548] Reaum i. 540.

[549] See above, VOL. I. 167--. II. 264.

[550] See above, VOL. I. p. 67.

[551] _N. Dict. d'Hist. Nat._ xvi. 269--. xxii. 76.

[552] Reaum. iv. 32. The author here quoted asserts that the grub of _Ichneumon Larvarum_ L. retains its skin, which, he says, is so transparent that the form of the nymph can be seen through it. Ibid. ii. 447. De Geer, however, found that this really did cast its skin, which is so transparent as to be scarcely visible, by pushing it gradually towards the anus, where it soon dries up and cannot then be discovered. De Geer ii. 893--. According to Rösel the same circumstance attends the transformation of _Coccinella renipustulata_ Illig. (_C. Cacti_ Ent. Brit.), which at first perplexed him not a little. It is probable that in this case the retention of the skin was accidental; for some of the grubs of a _Mycetophila_, the transformation of which I observed, became pupæ within their last skin, while others wholly disengaged themselves from it. The cause of this variation, I conjectured, arose from the former being too weak to extricate themselves from the skin.

[553] See above, VOL. I. p. 238. _Byrrhus Musæorum_ belongs to this genus.

[554] _N. Dict. d'Hist. Nat._ ii. 161.

[555] _Pezold._ 102.

[556] De Geer i. 339--.

[557] Reaum. ii. 423, and iii. 497.

[558] Ibid. i. 605.

[559] De Geer ii. 941.

[560] Brahm _Insek._ 72.

[561] Reaum. _ubi supra._

LETTER XXXI.

_STATES OF INSECTS._

PUPA STATE.

We have now traced our little animals through their egg and larva states, and have arrived at the third stage of their existence, _the Pupa State_. This, to include all, can only be defined,--that state intervening between the larva and imago, in which the parts and organs of the perfect insect, particularly those of sex, though in few cases fully developed, are prepared and fitted for their final and complete development in the last-mentioned state; and in which the majority of these animals are incapable of locomotion, or of taking food.

Pupæ, like larvæ, may be separated into two great divisions:--

I. Those which, in general form, more or less resemble the larvæ from which they have proceeded.

II. Those which are wholly unlike the larvæ from which they have proceeded.

I. To the first division belong, with some exceptions[562], the _Dermaptera_, _Orthoptera_, _Hemiptera_, and most _Aptera_, with the neuropterous tribes of _Libellulina_, _Ephemerina_, and the genus _Termes_, in the class _Insecta_; and the majority of the _Arachnida_. This, like the first division of larvæ, may be subdivided into two corresponding smaller sections; the first including those pupæ which resemble the larvæ, except in the relative proportion and number of some of their parts; and the second those that resemble them, except in having the rudiments of wings, or of wings and elytra.

i. The first subdivision will include the pupæ, if they may be so called[563], of insects of the _Aptera_ order, and of the class _Arachnida_: as, lice, _Poduræ_, _Lepismidæ_, centipedes, millipedes, mites, harvest-men, spiders, scorpions, &c. These mostly differ from their larvæ only in that the relative length or number of their legs, the number of the segments of the body in some, or the development of their palpi, more nearly approach the characters of the perfect insect; and in that while in their larva state they have two or more skins to cast, previously to their assumption of the imago, in their pupa state they have but one. In fact, this last circumstance is the only one which, strictly speaking, characterizes the pupæ of this subdivision; as the changes which take place in the number and proportion of the organs are partly produced with each change of the larva's skin. And hence, as it is not easy to ascertain what number of skins a spider, for example, has yet to cast, and as both the larva and pupa differ so little from the perfect insect, it is very difficult to determine in what state insects of this division are. From this difficulty has probably arisen the too great multiplication of species in some of these tribes, particularly the _Arachnida_, the larva and pupa having been mistaken for perfect insects. The pupæ of this subdivision were named by Linné _complete_, from the near resemblance which they bear to the imago.

ii. The second subdivision will include the pupæ of the _Dermaptera_, _Orthoptera_ and _Hemiptera_ orders, with few exceptions; as likewise the _Libellulina_, _Ephemerina_, and _Termitina_? amongst the _Neuroptera_: including the well-known tribes of earwigs, cockroaches, crickets, grasshoppers, locusts, lanthorn-flies, froghoppers (_Cicada_ L.), bugs, plant-lice, dragon-flies, day-flies, white ants, &c. Of these, as in the former subdivision, the pupæ are equally capable of eating and moving with the larvæ, which they resemble, except in having the rudiments of wings, or of wings and elytra. The pupæ of the three orders first enumerated differ from those of the _Neuroptera_ in resembling the perfect insect in most instances, both as to shape and the organs for taking their food; and in all other respects, except in not having their wings and elytra fully developed[564]. The resemblance of the pupæ of the _Libellulina_ and _Ephemerina_ to the perfect insects is more distant, and the above organs in the two states are very dissimilar; for the pupæ of the former are furnished with a prehensory mask similar to that of the larvæ before described[565], which the perfect insect has not; and those of the latter with the usual oral organs of masticating insects, of which the imago has scarcely the rudiments.

I have applied the term _rudiments_ to the wings and elytra in this state, not in a strict sense, but merely to denote their appearance; for in fact the wings, &c. are complete, but only folded up longitudinally and transversely, and inclosed in membranous cases, which when the last change takes place remain attached to the puparium or pupa-case. The tegmina or hemelytra in this state usually cover the wings, and the upper wings the under; but in the _Libellulina_ both are usually visible. Though commonly very small compared with the instruments of flight in the perfect insect, some of these rudiments, contrasted with the majority, are of considerable magnitude. This is the case with those of some species of _Chermes_, as we learn from De Geer[566].

II. The second grand division comprises by far the largest number of pupæ: those of all _coleopterous_, _strepsipterous_, _lepidopterous_, _hymenopterous_, _dipterous_, and _aphanipterous_, and by far the majority of _neuropterous_ insects, as well as the _hemipterous_ genus _Aleyrodes_, and one sex of _Coccus_ of the same order. These pupæ, however, though agreeing in the circumstance of being unlike the larvæ from which they proceed, differ from each other in several respects, and require to be divided into three great sections, as under:--

i. Those pupæ in which the _parts_ of the future insect, being folded up under a membranous skin closely applying to each, are distinctly _visible_. To this head belong generally, the pupæ of _coleopterous_[567] and _hymenopterous_ insects; those of the _neuropterous_ genera _Myrmeleon_ and _Hemerobius_, &c.; the _Trichoptera_; amongst the _Diptera_, _Culex_, _Tipula_ L., _Tabanus_, _Bombylius_, &c.; and that of the flea (_Pulex_). These were the _incomplete_ pupæ of Linné.

ii. Those pupæ in which the _parts_ of the future insect, being folded up under a harder skin, are _less_ distinctly _discoverable_. To this subdivision belong the pupæ of all _Lepidoptera_, and of them alone. These are what Linné termed _obtected_ pupæ.

iii. Those pupæ which are inclosed in the thick and opaque skin of the larva, through which no _trace_ of the perfect insect can be _discovered_. These, which Linné termed _coarctate_ pupæ, include a large proportion of the _dipterous_ genera; as _Œstrus_ L., _Musca_ L., _Empis_ L., _Conops_ L., &c. &c.[568]

I shall next advert, chiefly to the pupæ of the grand division last described, under the distinct heads of _substance_, _figure_, and _parts_; _colour_, _age_, _sex_, _motions_, and _extrication of the perfect insect_.

* * * * *

i. As to their _substance_--at first interiorly all pupæ consist of a milky fluid, in which the unformed members of the future perfect insect may be said to float, and in which they may be discerned, and separated with the point of a pin[569]. In proportion as these acquire consistency, and are more and more developed by the absorption of the surrounding fluid, they occupy its place, and fill up the cavity of the puparium. The rest of this fluid passes off by transpiration[570]. Reaumur is of opinion that it is from the epiploon, or _corps graisseux_, that this matter is prepared, which he regards as analogous to the white of an egg[571]. In _coarctate_ pupæ the included animal, or the pulp that contains its germes (in which the limbs and body at first are not discernible), fills at this period the whole skin-cocoon; but in proportion as the above evaporation takes place, and the consolidation of the body and parts proceeds, it shrinks at each end, so that when near assuming the imago, a considerable cavity appears both at the head and tail of the cocoon[572]. At this period of its existence, from the quantity of fluid included in the puparium, the animal weighs usually considerably more than it does when become a perfect insect[573].

The _exterior_ integument or _skin_ of pupæ, which is usually lined with a very thin white pellicle, is of different consistence in different orders. In the _Coleoptera_ and _Hymenoptera_ it is, with a few exceptions, of a soft and membranous texture; in the _Lepidoptera_ (especially those that are not defended by cocoons), and _Diptera_, it is more rigid and harder, being either coriaceous or corneous. Lepidopterous pupæ, however, are not excluded from the last skin of the larvæ with this hard covering. At the moment of this change the envelope is nearly as soft and membranous as in the order first mentioned. But they are besides covered with a viscous fluid, which appears to ooze out, chiefly from under the wings, and which very soon drying, forms the exterior hard shell[574]. At first the antennæ, wings, and legs, like those of _Coleoptera_ and _Hymenoptera_, can be each separated from the body; and it is only after these parts have been glued together by the fluid just mentioned, which takes place in less than twenty-four hours[575], that they are immoveably attached to the body of the pupa, as we usually see them. In fact, the essential difference between incomplete and obtected pupæ seems to be, that in the former the limbs and body are only covered each with a single membranous integument, whereas in the latter they are besides glued together by a substance which forms an additional and harder envelope. It is not easy to explain the alteration that takes place in the texture of the skin of such _dipterous_ pupæ as retain the skin of the larva. In the latter this is generally a transparent and very fine membrane: yet the very same integument becomes to the pupa an opaque and rigid case.

The surface of the skin of the greater number of pupæ is smooth, but in those of many _Papilionidæ_ it is rugose and warty: this you may see, particularly in that of _Papilio Machaon_. In many of the hawkmoths (_Sphinx_ L.) it is covered with impressed puncta. In _Attacus Io_ the upper side of the channels that separate the intermediate segments of the abdomen are curiously striated with transverse striæ, formed of very minute granula, the lower side being transversely sulcated. In some few instances, as in _Arctia Salicis_, _Laria pudibunda_ and _fascelina_, the skin of the pupa is clothed with hair[576]: as is also that of _Hesperia Bixæ_, according to Madame Merian[577]. De Geer has described a little beetle under the name of _Tenebrio lardarius (Latridius_ Latr., _Corticaria_ Marsh.), the pupa of which is beset with very fine hairs, terminating in a spherical or oval button[578].

ii. I shall include under the same head both the _figure_ or shape, and _parts_ of pupæ, as the latter in most kinds are either the same or nearly the same as those of the larva, or merely incasing those of the imago, so as not to require that detailed notice that I judged necessary when treating of the parts of larvæ.

With regard to _incomplete_ pupæ, nothing further can be said of their extremely various _figure_, than that it has a general resemblance to that of the perfect insect. The head, trunk, abdomen, and their respective external organs, are alike visible in both; but in the pupæ, the latter, instead of occupying their natural situation, are all closely folded under the breast and abdomen: or, as in the case of the long ovipositors of some Ichneumons, laid along the back. In a specimen of some coleopterous insect now before me, the following is the order of the arrangement of the parts:--The head is inflexed; the mandibulæ are open; between them are seen the labium and labial palpi; these appear to cover and conceal the maxillæ, and the maxillary palpi extend on each side beyond them; the antennæ pass above the thighs of the two anterior pair of legs, and then turning down over the breast between them and the posterior legs, repose upon the base of the wings; which also are turned down between the intermediate and posterior pair of legs, and rest upon the latter; the tibiæ are bent in and folded upon the thigh, and the tarsi turn outwards[579]. In another coleopterous species, the wings and elytra are placed under the hind-legs. In _Hymenopterous_ pupæ the antennæ appear usually to lie between the legs[580]. In many _Tipulæ_ the long legs are bent into three folds in the pupæ; but the tarsi are extended, and lie close to each other, the anterior pair being the shortest[581]. In a specimen belonging to this tribe in my cabinet, which I think contained _Ctenocera pectinicornis_, the six leg-cases are of the same length, exactly parallel and adjacent, and being annulated wear the appearance of tracheæ[582]. These parts have each their separate case, so that a pin may be introduced between them and the body: which cases, as well as the general envelope, are usually formed of a fine soft transparent membrane; but sometimes, as in the lady-bird (_Coccinella_), the tortoise-beetle (_Cassida_), the crane-fly (_Tipula_), &c. it is harder and more opaque, so that though it is usually easy for a practised Entomologist from an examination of the pupa, particularly in the _Hymenoptera_, to predict to what genus the insect to be disclosed from them will belong, yet in these cases the organs being not so conspicuous, a less experienced examiner might be perplexed, and unable to come to a conclusion.

Although _hymenopterous_ pupæ have usually no parts but what are afterwards seen in the perfect insect, this is not the case with several _coleopterous_ and _dipterous_ ones, which are furnished with various temporary appendages, indispensable to them to bring about their final change, or for other purposes. Thus, the pupa of the male of _Lucanus Cervus_ has two short, jointed anal processes[583]. That of _Hydrophilus caraboides_ has a pedunculated lunulate one; and moreover, the sides of the abdominal segments, and the top of the thorax, are beset with hairs, which are not seen in the perfect insect[584]. The abdomen of many, also, is armed with spines. That, the arrangement of whose organs I lately described, has a quadruple series in the back of this part; viz. on each of the first five segments, 3, 2, 2, 3. The five first ventral segments also have on each side three spines; the inner are incurved, the intermediate nearly upright, and the outer one recurved. These spines, except those of the innermost ventral series, terminate in a bristle. In another coleopterous species the back part of the head is armed with a pair of lateral spines, and that of the thorax with three processes, the external ones armed with a single spine, and the intermediate one with a pair. De Geer has figured the pupa of an _Asilus_, the head of which is armed with eight spines--two robust ones in front, and three smaller ones, connected at the base on each side. The abdominal segments, also, are fringed with spines[585]. The abdomen of the pupa of _Ctenocera pectinicornis_ is armed with several strong conical spines, pointing mostly towards the tail, which is likewise the case with that of _Tipula lunata_[586]. As the above pupæ are usually subterranean or subcortical, the spines assist in pushing them out of the ground, &c. The respiratory horns that proceed from the thorax of the pupæ of many of the aquatic gnats will be noticed in another place. Those of _Corethra culiciformis_ and of some other aquatic gnat-like _Diptera_, have their anus furnished with a pair of oars, or natatory laminæ, by which they rise to the surface[587].

The figure of _obtected_ pupæ, or chrysalises, is more uniform. They are commonly obtuse at the anterior extremity, and gradually contracted to a point at the posterior, or tail. The outline usually inclines to a long oval or an ellipse; but in some, as _Attacus Io_ and _Luna_, the pupa is shorter and more spherical. In _Geometra sambucaria_ it represents an elongated cone, and in _Hepialus_ it is nearly cylindrical. In the butterfly tribe (_Papilio_ L.) the outline is frequently rendered angular by various protuberances.

In all these pupæ may be distinguished the following parts:--_first_, the _Head-case_ (_Cephalo-theca_), or anterior extremity; _secondly_, the _Trunk-case_ (_Cyto-theca_), or intermediate part; and _thirdly_, the _Abdomen-case_ (_Gastro-theca_).

1. The _Head-case_ covers and protects the _head_ of the inclosed imago. From its sides behind proceed the antennæ-cases (_Cera-theca_); and before from the middle, the tongue-case (_Glosso-theca_). Just below the base of the antennæ-case you may discern the eye-cases (_Ophthalmo-theca_), surrounded on their inner side by a crescent-shaped lævigated piece, which may perhaps transmit some light to the inclosed prisoner.