I alluded, is chiefly remarkable for the element in which it is
constructed and the materials that compose it. It is built in the
midst of water, and formed, in fact, of air! Spiders are usually
terrestrial, but this is aquatic, or rather amphibious; for though
she resides in the midst of water, in which she swims with great
celerity, sometimes on her belly but more frequently on her back,
and is an admirable diver, she not unfrequently hunts on shore,
and, having caught her prey, plunges with it to the bottom of the
water. Here it is she forms her singular and unique abode. She would
evidently have but a very uncomfortable time were she constantly wet,
but this she is sagacious enough to avoid; and by availing herself of
some well-known philosophical principles, she constructs for herself
an apartment in which, like the mermaids and sea-nymphs of fable,
she resides in comfort and security. The following is her process.
First she spins loose threads in various directions attached to the
leaves of aquatic plants, which may be called the frame-work of her
chamber, and over them she spreads a transparent varnish resembling
liquid glass, which issues from the middle of her spinners, and which
is so elastic that it is capable of great expansion and contraction:
and if a hole be made in it, it immediately closes again. Next she
spreads over her belly a pellicle of the same material, and ascends
to the surface. The precise mode in which she transfers a bubble
of air beneath this pellicle is not accurately known; but from an
observation made by the ingenious author of the little work from
which this account is abstracted, he concludes that she draws the
air into her body by the anus, which she presents to the surface of
the pool, and then pumps it out from an opening at the base of the
belly between the pellicle and that part of the body, the hairs of
which keep it extended. Clothed with this aërial mantle, which to
the spectator seems formed of resplendent quicksilver, she plunges
to the bottom, and, with as much dexterity as a chemist transfers
gas with a gas-holder, introduces her bubble of air beneath the
roof prepared for its reception. This manœuvre she repeats ten or
twelve times, until at length in about a quarter of an hour she has
transported as much air as suffices to expand her apartment to its
intended extent, and now finds herself in possession of a little
aërial edifice, I had almost said an enchanted palace, affording her
a commodious and dry retreat in the very midst of the water. Here
she reposes unmoved by the storms that agitate the surface of the
pool, and devours her prey at ease and in safety. Both sexes form
these lodgings. At a particular season of the year the male quits his
apartment, approaches that of the female, enters it, and enlarging it
by the bubble of air that he carries with him, it becomes a common
abode for the happy pair[818].--The spider which forms these singular
habitations is one of the largest European species, and in some
countries not uncommon in stagnant pools.
I am, &c.
FOOTNOTES:
[758] _Melitta._ *. a. K.
[759] Grew's _Rarities of Gresham Colledge_, 154. Kirby, _Mon. Ap.
Angl._ i. 131. _Melitta._ *. a.
[760] Curtis _Brit. Ent. t._ 61.
[761] _Mon. Ap. Angl._ i. 173. _Apis._ **. c. 2. α. From later
observations I am inclined to think that these cells may possibly,
as in the case of the humble-bee, be in fact formed by the larva
previously to becoming a pupa, after having eaten the provision of
pollen and honey with which the parent bee had surrounded it. The
vermicular shape, however, of the masses with which the cases are
surrounded, does not seem easily reconcileable with this supposition,
unless they are considered as the excrement of the larva.
[762] _Apis._ **. d. 2. β. K.
[763] Reaum. vi. 39-50. _Mon. Ap. Angl._ i. 189. _Apis._ **. α. 2. β.
[764] _Ann. du Mus._ x. 236.
[765] Reaumur plausibly supposes that it has been from observing this
bee thus loaded, that the tale mentioned by Aristotle and Pliny, of
the hive-bee's ballasting itself with a bit of stone previously to
flying home in a high wind, has arisen.
[766] Reaum. vi. 57-88. _Mon. Ap. Angl._ i. 179.
[767] _Apis._ **. c. 2. δ. K.
[768] _Apis._ **. c. 2. α. K.
[769] Reaum. vi. 139-148.
[770] Latr. _Hist. Nat. des Fourmis_, 297.
[771] Reaum. vi. 971-24. _Mon. Ap. Angl._ i. 157. Apis. **. c. 2. α.
[772] Reaum. vi. 251-7. _t._ xxvi. _f._ 1.
[773] Latr. _Fourmis_, 419.
[774] See above, p. 317--.
[775] Aikin's _Dictionary of Chemistry_, i. 455. What have probably
been taken by Mr. Aikin for "kernels," in the imperforated nuts, are
the cocoons of the inhabitants of these galls in the pupa state,
which often extremely resemble the seeds of a capsule, as Reaumur
(iii. 429.) has remarked.
[776] Reaum. iii. 417, &c.
[777] _Introd. to Botany_, 349.
[778] Reaum. iii. 474.
[779] Ibid. 479.
[780] Ibid. 501.
[781] Ibid. 479.
[782] _De Insectis_, 233 &c.
[783] Reaum. iii. t. 38. f. 2, 3.
[784] Ibid. iii. 448.
[785] Ibid. 455.
[786] De Geer, vi. 409.
[787] De Geer, vi. 421.
[788] Jacquin _Collect._ ii. 255.
[789] Reaum. iii. 427.
[790] Lyonet, _Anat. of Coss._ 9.
[791] P. 307, 392.
[792] Lewin's _Prodromus Entomology_ (sic!), p. 8.
[793] Bonnet, ix. 188.
[794] Reaum. iii. 100-120.
[795] Ibid. 146.
[796] Forsyth _on Fruit Trees_, 4to edit. 271.
[797] Goeze _Natur. Menschenleben und Vorsehung_. Anderson's
_Recreations_, ii. 409. See above p. 16.
[798] Reaum. iii. 206. PLATE XVII. FIG. 9.
[799] Germar's _Mag. für Entomologie_, i. 40.
[800] x. 458.
[801] Reaum. iii. 183.
[802] The larvæ of the males intermix with the pieces of twigs, which
are less closely and regularly arranged, bits of dried leaves and other
light materials. See the excellent elucidation of the history of this
tribe, whose mode of generation is so singular, by Von Scheven, in the
_Naturforscher_ Stk. xx. 61, &c. also a valuable paper by Dr. Zincken
genannt Sommer, in Germar's _Mag. für Ent._ i. 19-40.
[803] Reaum. iii. 148-9. T. 11. f. 10. 11.
[804] Fuessly, _Archiv._ 53. _t._ 31. Germar's _Mag. für Ent._ i. 136.
[805] See above, p. 165.
[806] Aristot. _Hist. Anim._ l. viii. c. 27.
[807] Reaum. iii. mem. 8.
[808] _Nat. Theol._ 230.
[809] Reaum. iii. 130.
[810] PLATE XVII. FIG. 10.
[811] Reaum. iii. 156-9.
[812] Sowerby's _Nat. Miscell._ _No._ ix. _t._ 51.
[813] De Geer, ii. 564.
[814] De Geer, ii. 564.
[815] Reaum. iii. 179.
[816] Sauvages _Hist. de l'Acad. des Sc. de Paris_, 1758, p. 26.
Perhaps this, as well as _M. cæmentaria_, belongs to Latreille's
genus _Cteniza_. _Familles Naturelles du Règne Animal_, 313.
[817] Latr. _Hist. Nat._ vii. 165.
[818] _Mémoire pour servir à commencer l'Histoire des Araignées
Aquatiques_, 12mo.
LETTER XV.
_HABITATIONS OF INSECTS
CONTINUED._
The habitations of insects which I shall next proceed to describe,
are those formed by the united labour of several individuals.
The societies which thus combine their operations may be divided into
two kinds: 1st, those of which the object is simply the conservation
of the individuals composing them; and 2dly, those whose object is
also the nurture and education of their young. To the last head
belong bees, wasps, &c.: to the former the larvæ of some species of
moths, whose labours being the most simple I shall first describe.
* * * * *
You cannot fail to have observed in gardens the fruit-trees disfigured,
as you would probably think them, with what at first view seem very
strong and thick spiders' webs. If you have bestowed upon these webs
the slightest attention, you must have likewise remarked that they
differ very materially in their construction from those spun by
spiders, inclosing on every side an angular space, and being besides
filled with caterpillars. These are the larvæ of _Arctia chrysorrhœa_,
and the web which contains them is spun by their united labour for
the protection of the common society. As soon as the cluster of eggs
deposited by the parent moth is hatched, the young caterpillars, to the
number of three or four hundred, commence their operations. At first
they content themselves by forming a sort of hammock of the single
leaf upon which they find themselves assembled, covering it with a
roof composed of a number of silken threads drawn from one edge to
the other; and under one or more of these temporary habitations they
reside for a few days, until they are become large and strong enough
to undertake a more solid and spacious building sufficient to contain
the whole society. In constructing this new habitation, they spin a
close silken web round the end of two or three adjoining twigs and the
leaves attached to them, so as to include the requisite space. They are
not curious in giving any particular form to the edifice: sometimes it
is flat, often roundish, but always more or less angular. The interior
is divided by partitions of silk into several irregular apartments,
to each of which there is purposely left an appropriate door. Within
these the caterpillars retire at night, or in rainy weather, quitting
the nest on fine days, and dispersing themselves over the neigbouring
leaves, upon which they feed. Here too they repose during the critical
period of the change of their skins. On the approach of winter the
whole community shut themselves up in the nest, which, by the addition
of repeated layers of silk, has at this time become so thick and strong
as to be impervious to the wind and rain. They remain in a state of
torpidity during the cold months, but towards the beginning of April
are awakened to activity by the genial breath of spring, and begin
to feed with greediness upon the young leaves that surround their
habitation, which, as they soon greatly increase in size, they find
it necessary to enlarge. One might fear that a structure formed of
such materials would at this period be sadly damaged by the growth of
the young shoots and leaves of the twigs which it incloses; but the
inhabitants, as if to guard against such an accident, have gnawed off
all the buds within their dwelling, and thus secured themselves from
this inconvenience[819].
The nest of the larvæ of another species of moth, the _Lasiocampa
processionea_, unfortunately not a native of this country, to which
on account of their singular manners, that will be detailed to you in
a subsequent letter, Reaumur has given the title of _processionary_
caterpillars, is somewhat different in its construction from
that just described, though formed of the same material. As the
caterpillars which fabricate it feed upon the leaves of the oak, it
is always found upon this tree, attached not to the branches but the
trunk, sometimes at a considerable height from the ground. In shape
it resembles an irregular knob or protuberance, and the silk which
composes it being of a gray colour, at a distance it would be taken
for a mass of lichens. Sometimes this nest is upwards of eighteen
inches long, and six broad, rising in the middle about four inches
from the surface of the tree. Between the trunk and the silken
covering, a single hole is left which serves for the entrance and
exit of the inhabitants. These differ in their manners from those
last mentioned. While very young they have no fixed habitation,
contenting themselves with a succession of different temporary camps
until they have attained two-thirds of their growth. Then it is they
unite their labours in spinning the nest just described; and in this
they continue to reside in harmony until they become perfect insects,
assuming in it even the state of chrysalis[820].
Habitations similar, as to their general structure, to the above,
though differing in several minute circumstances, are formed by
the larvæ of several other moths, as of _Arctia phæorrhœa_ of
Curtis, _Trichoda neustria_, &c. as well as those of _Vanessa Io_,
_Melitæa Cinxia_, and some other butterflies: and even of some
saw-flies (_serrifera_), which, however, have each a separate silken
covering. But as it would be tedious to describe these particularly,
I pass on to the habitations formed by insects in their perfect
state, which have in view the education of their young as well as
self-preservation, describing in succession those of _ants_, _bees_,
_wasps_, and _white-ants_.
* * * * *
Of these the most simple in their structure are the nests of different
kinds of _ants_, many of which externally present the appearance of
hillocks more or less conical, formed of earth or other substances.
The nest of the large red or horse ants (_F. rufa_,) which are common
in woods, at the first aspect seems a very confused mass. Exteriorly
it is a conical mount composed of pieces of straw, fragments of wood,
little stones, leaves, grain; in short, of any portable materials
within their reach. But however rude its outward appearance, and the
articles of which it consists, interiorly it presents an arrangement
admirably calculated at once for protection against the excessive
heat of the sun, and yet to retain a due degree of genial warmth. It
is wholly composed of numerous small apartments of different sizes,
communicating with each other by means of galleries and arranged in
separate stories, some very deep in the earth, others a considerable
height above it: the former for the reception of the young in cold
weather and at night, the latter adapted to their use in the day time.
In forming these, the ants mix the earth excavated from the bottom of
the nest with the other materials of which the mount consists, and
thus give solidity to the whole. Besides the avenues which join the
apartments together, other galleries varying in dimensions communicate
with the outside of the nest at the top of the mount. These open doors
would seem ill calculated for precluding the admission of wet or of
nocturnal enemies: but the ants alter their dimensions continually
according to circumstances; and they wholly close them at night, when
all gradually retire to the interior, and a few sentinels only are left
to guard the gates. On rainy days, too, they keep them shut, and when
the sky is cloudy open them partially[821].
The habitations of these ants are much larger than those of any other
species in this country, and sometimes as big as a small haycock;
but they are mere molehills when compared with the enormous mounds
which other species apparently of the same family, but much larger,
construct in warmer climates. Malouet states, that in the forests
of Guiana he once saw ant-hills which, though his companion would
not suffer him to approach nearer than forty paces for fear of his
being devoured, seemed to him to be fifteen or twenty feet high, and
thirty or forty in diameter at the base, assuming the form of a
pyramid, truncated at one-third of its height[822], and Stedman, when
in Surinam, once passed ant-hills six feet high, and at least one
hundred feet in circumference[823].
The nest of _Formica brunnea_ is composed wholly of earth, and
consists of a great number of stories, sometimes not fewer than
forty, twenty below the level of the soil, and as many above,
which last, following the slope of the ant-hill, are concentric.
Each story, separately examined, exhibits cavities in the shape of
saloons, narrower apartments, and long galleries which preserve the
communication between both. The arched roofs of the most spacious
rooms are supported by very thin walls, or occasionally by small
pillars and true buttresses; some having only one entrance from
above, others a second communicating with the lower story. The main
galleries, of which in some places several meet in one large saloon,
communicate with other subterranean passages, which are often carried
to the distance of several feet from the hill.--These insects work
chiefly after sunset.--In building their nest they employ soft clay
only, scraped from its bottom when sufficiently moistened by a
shower, which, far from injuring, consolidates and strengthens their
architecture. Different labourers convey small masses of this ductile
material between their mandibles, and with the same instruments they
spread and mould it to their will, the antennæ accompanying every
movement. They render all firm by pressing the surface lightly with
their fore feet; and however numerous the masses of clay composing
these walls, and though connected by no glutinous material, they
appear when finished one single layer well united, consolidated,
and smoothed. Having traced the plan of their structure, by placing
here and there the foundations of the pillars and partition-walls,
they add successively new portions: and when the walls of a gallery
or apartment which are half a line thick are elevated about half
an inch in height, they join them by springing a flattish arch or
roof from one side to the other. Nothing can be a more interesting
spectacle than one of these cities while building. In one place
vertical walls form the outline, which communicate with different
corridors by openings made in the masonry; in another we see a true
saloon whose vaults are supported by numerous pillars; and further on
are the cross ways or squares where several streets meet, and whose
roofs, though often more than two inches across, the ants are under
no difficulty in constructing, beginning the sides of the arch in the
angle formed by two walls, and extending them by successive layers
of clay till they meet; while crowds of masons arrive from all parts
with their particle of mortar, and work with a regularity, harmony,
and activity, which can never enough be admired. So assiduous are
they in their operations, that they will complete a story with all
its saloons, vaulted roofs, partitions and galleries, in seven
or eight hours. If they begin a story, and for want of moisture
are unable to finish it, they pull down again all the crumbling
apartments that are not covered in[824].
Another species of ants (_F. fusca_) are also masons. When they wish to
heighten their habitations, they begin by covering the top with a thick
layer of clay which they transport from the interior. In this layer
they trace out the plan of the new story, first hollowing out little
cavities of almost equal depth at different distances from each other,
and of a size adapted to their purposes. The elevations of earth left
between them serve for bases to the interior walls, which, when they
have removed all the loose earth from the floors of the apartments, and
reduced the foundations to a due thickness, they heighten, and lastly
cover all in. M. Huber saw a single working ant make and cover in a
gallery which was two or three inches long, and of which the interior
was rendered perfectly concave, without assistance[825].
The societies of _F. fuliginosa_ make their habitations in the
trunks of old oaks or willow-trees, gnawing the wood into numberless
stories more or less horizontal, the ceilings and floors of which
are about five or six lines asunder, black, and as thin as card,
sometimes supported by vertical partitions, forming an infinity of
apartments which communicate by small apertures; at others by small
light cylindrical pillars furnished with a base and capital which
are arranged in colonnades, leaving a communication perfectly free
throughout the whole extent of the story[826].
Two other tribes of carpenter ants (_F. æthiops_ and _F. flava_) use
saw-dust in forming their buildings. The former applies this material
only to the building of walls and stopping up chinks: the latter
composes whole stages or stories of it made into a sort of _papier
mâché_, with earth and spiders' web[827].
Some ants form their nests of the leaves of trees. One of these was
observed by Sir Joseph Banks in New South Wales, which was formed
by glueing together several leaves as large as a hand. To keep these
leaves in a proper position, thousands of ants united their strength,
and if driven away, the leaves spring back with great violence[828].
* * * * *
The most profound philosopher, equally with the most incurious of
mortals, is struck with astonishment on inspecting the interior of a
_bee-hive_. He beholds a city in miniature. He sees this city divided
into regular streets, these streets composed of houses constructed on
the most exact geometrical principles and the most symmetrical plan,
some serving for store-houses for food, others for the habitations of
the citizens, and a few, much more extensive than the rest, destined
for the palaces of the sovereign. He perceives that the substance of
which the whole city is built, is one which man, with all his skill,
is unable to fabricate; and that the edifices in which it is employed
are such, as the most expert artist would find himself incompetent to
erect. And the whole is the work of a society of insects! "_Quel abîme_
(he exclaims with Bonnet) _aux yeux du sage qu'une ruche d'Abeilles!
Quelle sagesse profonde se cache dans cet abîme! Quel philosophe osera
le fonder!_" Nor have its mysteries yet been fathomed. Philosophers
have in all ages devoted their lives to the subject; from Aristomachus
of Soli in Cilicia, who, we are told by Pliny, for fifty-eight years
attended solely to bees, and Philiscus the Thracian, who spent his
whole time in forests investigating their manners, to Swammerdam,
Reaumur, Hunter, and Huber of modern times. Still the construction of
the combs of a bee-hive is a miracle which overwhelms our faculties.
You are probably aware that the hives with which we provide bees
are not essential to their labours, and that they can equally form
their city in the hollow of a tree or any other cavity. In whatever
situation it is placed, the general plan which they follow is the
same. You have seen a honey-comb, and must have observed that it is a
flattish cake, composed of a vast number of cells, for the most part
hexagonal, regularly applied to each other's sides, and arranged in
two strata or layers placed end to end. The interior of a bee-hive,
consists of several of these combs fixed to its upper part and sides,
arranged _vertically_ at a small distance from each other, so that
the cells composing them are placed in a horizontal position, and
have their openings in opposite directions--not the best position
one would have thought for retaining a fluid like honey, yet the
bees find no inconvenience on this score. The distance of the combs
from each other is about half an inch, that is, sufficient to allow
two bees busied upon the opposite cells to pass each other with
facility. Besides these vacancies, which form the high roads of
their community, the combs are here and there pierced with holes
which serve as posterns for easy communication from one to the other
without losing time by going round.
The arrangement of the combs is well adapted for its purpose, but
it is the construction of the cells which is most admirable and
astonishing. As these are formed of wax, a substance secreted by the
bees in no great abundance, it is important that as little as possible
of such a precious material should be consumed. Bees, therefore,
in the formation of their cells have to solve a problem which would
puzzle some geometers, namely, a quantity of wax being given, to form
of it similar and equal cells of a determinate capacity, but of the
largest size in proportion to the quantity of matter employed, and
disposed in such a manner as to occupy in the hive the least possible
space. Every part of this problem is practically solved by bees. If
their cells had been cylindrical, which form seems best adapted to the
shape of a bee, they could not have been applied to each other without
leaving numberless superfluous vacuities. If the cells were made
square or triangular, this last objection, indeed, would be removed;
but besides that a greater quantity of wax would have been required,
the shape would have been inconvenient to a cylindrical-bodied animal.
All these difficulties are obviated by the adoption of hexagonal
cells, which are admirably fitted to the form of the insect, at the
same time that their sides apply to each other without the smallest
vacant intervals.--Another important saving in materials is gained
by making a common base serve for two strata of cells. Much more wax
as well as room would have been required, had the combs consisted of
a single stratum only. But this is not all. The base of each cell is
not an exact plane, but is usually composed of three rhomboidal or
lozenge-shaped pieces, placed so as to form a pyramidal concavity. From
this form it follows that the base of a cell on one side or stratum of
the comb is composed of portions of the bases of _three_ cells on the
other. You will inquire, Where is the advantage of this arrangement?
First, a greater degree of strength; and secondly, precisely the same
as results from the hexagonal sides--a greater capacity with less
expenditure of wax. Not only has this been indisputably ascertained,
but that the angles of the base of the cell are exactly those which
require the smallest quantity of wax. It is obvious that these angles
might vary infinitely; but by a very accurate admeasurement Maraldi
found, that the great angles were in general 109° 28', the smaller
ones 70° 32'. Reaumur ingeniously suspecting that the object of
choosing these angles from amongst so many was to spare wax, proposed
to M. Kœnig, a skilful geometrician, who was ignorant of Maraldi's
experiments, to determine by calculations what ought to be the angle
of a hexagonal cell, with a pyramidal bottom formed of three similar
and equal rhomboid plates, so that the least matter possible might
enter into its construction. For the solution of this problem the
geometrician had recourse to the infinitesimal calculus, and found that
the great angles of the rhombs should be 109° 26', and of the small
angles 70° 34'[829]. What a surprising agreement between the solution
of the problem and the actual admeasurement[830]!