_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.
2. The _Trunk-case_, divided into the _thorax_, or _upper_ surface,
extending from the head to the dorsal segments of the abdomen,
and consisting of three pieces, answering to the _prothorax_,
_mesothorax_, and _metathorax_ of the perfect insect: the first
answering to the prothorax small, the second covering the mesothorax
very large, and the two next representing the metathorax, at first
appearing to belong to the abdomen, but having no spiracle; and
the breast (_pectus_) or under-surface reaching from the head to
the ventral abdominal segments, from which proceed the wing-cases
(_Ptero-theca_) and leg-cases (_Podo-theca_), which organs, with the
antenna-cases and tongue-case, entirely cover, or rather form, the
breast. The arrangement of the whole is as follows:--The wing-cases,
which are more or less triangular, and exhibit the larger nervures of
the wings, are a lateral continuation of the mesothorax, which turn
downwards from the sides of the breast, and cover, or replace, the
three first ventral segments of the abdomen. The _antenna-cases_,
united to the anterior portion of the head just behind the eye-cases,
repose immediately next to those of the wings running parallel with
their inner margin. Then follow the legs, the tibiæ forming an angle
with the thigh, and the case of the anterior pair being innermost,
and representing the breast-bone in the pupa. The tongue lies over
the forelegs, except in the case of some sphinxes, which I shall
notice afterwards: so that the glosso-theca covers both them and it.