of an anonymous author in the _Journal de Physique_[745], founded
as he asserts on actual observation. He says that he saw a small
spider, which he had forced to suspend itself by its thread from
the point of a feather, shoot out obliquely in opposite directions
other smaller threads, which attached themselves in the still air of
a room, without any influence of the wind, to the objects towards
which they were directed. He therefore infers that spiders have
the power of shooting out threads and directing them at pleasure
towards a determined point, judging of the distance and position of
the object by some sense of which we are ignorant. Something like
this manœuvre I once myself witnessed in a male of the small garden
spider (_Epeira? reticulata_). It was standing midway on a long
perpendicular fixed thread, and an appearance caught my eye of what
seemed to be the emission of threads from its projected spinners.
I therefore moved my arm in the direction in which they apparently
proceeded, and, as I suspected, a floating thread attached itself to
my coat, along which the spider crept. As this was connected with the
spinners of the spider, it could not have been formed in the same way
with the secondary thread of _E. Diadema_ above described.
Probably in this case, as in so many others, we bewilder ourselves by
attempting to make nature bend to generalities to which she disdains
to submit. Different spiders may lay the foundations of their net in a
different manner; some on the plan adopted by _E. Diadema_; others, as
Lister long ago conjectured[746], by shooting out threads in the mode
of the flying species, as in the instances recorded by the anonymous
observer, and Mr. Knight. Nor is it improbable that the same species
has the power of varying its procedures according to circumstances.
How far these suppositions are correct it is impossible to determine
without further experiments, which it is somewhat strange should
not before now have been instituted. Pliny thought it nothing to
the credit of the philosophers of his day, that while they were
disputing about the number of heroes of the name of Hercules, and
the site of the sepulchre of Bacchus, they should not have decided
whether the queen bee had a sting or not[747]; but it seems much more
discreditable to the entomologists of ours, that they should yet be
ignorant how the geometric spiders fix their nets. One excuse for
them is, that these insects generally begin their operations in the
night, so that, though it is very easy to see them spinning their
concentric circles, it is seldom that they can be caught laying the
foundations of their snares. Yet doubtless the lucky moment might
be hit by an attentive observer, and I shall be glad if my attempt
to describe their more ordinary operations should induce you to aim
at signalizing yourself by the discovery. If you failed in solving
every difficulty, you would at least be rewarded by witnessing their
industry, ingenuity, and patience.
For the latter virtue they have no small occasion. Incapable of
actively pursuing their prey, they are dependent upon what chance
conducts into their toils, which, especially those spread in
neglected buildings, often remain for a long period empty. Even
the geometrical spiders, which fix themselves in the midst of a
well-peopled district in the open air, have frequently to sustain
a protracted abstinence. A continued storm of wind and rain will
demolish their nets, and preclude the possibility of reconstructing
them for many days or sometimes weeks, during which not a single
gnat regales their sharp-set appetites. And when at length formed
anew or repaired, an unlucky bee or wasp, or an overgrown fly, will
perversely entangle itself in toils not intended for insects of its
bulk, and in disengaging itself once more leave the net in ruin.--All
these trials move not our philosophic race. They patiently sit in
their watching-place in the same posture, scarcely ever stirring but
when the expected prey appears. And however repeatedly their nets are
injured or destroyed, as long as their store of silk is unexhausted,
they repair or reconstruct them without loss of time.
The web of a house spider will, with occasional repairs, serve for
a considerable period; but the nets of the geometric spiders are
in favourable weather renewed either wholly, or at least their
concentric circles, every twenty-four hours, even when not apparently
injured. This difference in the operations of the two tribes depends
upon a very remarkable peculiarity in the conformation of their
snares. The threads of the house spider's web are all of the same
kind of silk, and flies are caught in them from their claws becoming
entangled in the fine meshes which form the texture. On the other
hand the net of the garden spider is composed of two distinct
kinds of silk; that of the radii not adhesive, that of the circles
extremely viscid[748]. The cause of this difference, which, when
it is considered that both sorts of silk proceed from the same
instrument, is truly wonderful, may be readily perceived. If you
examine a newly formed net with a microscope, you will find that the
threads composing the outline and the radii are simple, those of the
circles closely studded with minute dew-like globules, which from the
elasticity of the thread are easily separable from each other. That
these are in fact globules of viscid gum, is proved by their adhering
to the finger and retaining dust thrown upon the net, while the
unadhesive radii and exterior threads remain unsoiled. It is these
gummed threads alone which retain the insects that fly into the net;
and as they lose their viscid properties by the action of the air, it
is necessary that they should be frequently renewed.
In this renewal, as above hinted, the geometrical spiders are
constantly regulated by the future probable state of the atmosphere,
of which they have such a nice perception, that M. Q. D'Isjonval,
to whom we are indebted for the fact, has proposed them as most
accurate barometers. He asserts that if the weather be about to
be variable, wet and stormy, the main threads which support the
net will be certainly short; but if fine settled weather be on
the point of commencing, these threads will be as invariably very
long[749]. Without going the length with M. D'Isjonval of deeming his
discoveries important enough to regulate the march of armies, or the
sailing of fleets, or of proposing that the first appearance of these
barometrical spiders in spring should be announced by the sound of
trumpet, I have reason to suppose from my own observations that his
statements are in the main accurate, and that a very good idea of
the weather may be formed from attending to these insects.
The spiders which form geometrical nets differ from the weavers also
with respect to the situation in which they watch for their prey.
They do not conceal themselves under their net, but are placed in the
centre with their head downwards, and retire to a little apartment
formed on one side under some leaf of a plant, only when obliged by
danger or the state of the weather. The moment an unfortunate fly or
other insect touches the net, the spider rushes towards it, seizes
it with her fangs, and if it be a small species at once carries it
to her little cell, and, having there at leisure sucked its juices,
throws out the carcase. If the insect be larger and struggle to
escape, with surprising address she envelops it with threads in
various directions, until both its wings and legs being effectually
fastened, she carries it off to her den. If the captured insect be a
bee or a large fly so strong that the spider is sensible it is more
than a match for her, she never attempts to seize or even entangle
it, but on the contrary assists it to disengage itself, and often
breaks off that part of the net to which it hangs, content to be rid
of such an unmanageable intruder at any price.--When larger booty
is plentiful, these spiders seem not to regard smaller insects. I
have observed them in autumn, when their nets were almost covered
with the Aphides which filled the air, impatiently pulling them off
and dropping them untouched over the sides, as though irritated that
their meshes should be occupied with such insignificant game.--A
species of spider described by Lister, (_Epeira conica_,) more
provident than its brethren, suspends its prey in the meshes above
and below the centre, and it is not uncommon to see its larder thus
stored with several flies[750].
You must not infer that the toils of spiders are in every part of the
world formed of such fragile materials as those which we are accustomed
to see, or that they are every where contented with small insects for
their food. An author in the _Philosophical Transactions_ asserts,
that the spiders of Bermudas spin webs between trees seven and eight
fathoms distant, which are strong enough to ensnare a bird as large as
a thrush[751]. And Sir G. Staunton informs us, that in the forests of
Java, spiders' webs are met with of so strong a texture as to require a
sharp-cutting instrument to make way through them[752].
Nor must you suppose that all the spiders of this country which
catch their prey by means of snares, follow the same plan in
constructing them as the weavers and geometricians whose operations
I have endeavoured to describe. The form of their snares and the
situation in which they place them are so various, that it is
impossible to enumerate more than a few of the most remarkable.
_Agelene labyrinthica_ extends over the blades of grass a large white
horizontal net having at its margin a cylindrical cell, in the bottom
of which, secure from birds and defended from the rays of the sun,
the spider lies concealed, whence on the slightest movement of her
net she rushes out upon her prey. _Aranea latens_, F. conceals itself
under a small net spun upon the upper surface of a leaf, and thence
seizes upon any insect that chances to pass over it. _Theridium_
13-_guttatum_ forms under stones and in slight furrows in the
ground a net consisting of threads spun without any regularity in
all directions, but so strong as to entrap grasshoppers, which are
said to be its principal food; and a similar inartificial snare of
simple threads is often spun in windows by _Theridium bipunctatum_
and several other species. _Segestria senoculata_ and its affinities
conceal themselves in a long cylindrical straight silken tube, from
the mouth of which they stretch out their six anterior feet, whose
extremities rest upon as many diverging threads: thus, as soon as an
insect walks across any of the threads (which are eight or ten inches
long) the insect's toes give it warning of prey being at hand, when
it rushes out and seldom fails to secure its victim.
"The spider's touch how exquisitely fine!
Feels at each thread, and lives along the line."
M. Homberg tells us that he has seen a vigorous wasp carried off and
destroyed by one of these species.
* * * * *
The spiders, to which I have hitherto adverted, seize their prey by
means of webs or nets; but a very large number, though, like the
former, they spin silken cocoons for containing their eggs, never
employ the same material in constructing similar snares, of which
they make no use.
These may be separated into two grand divisions: the first comprising
those which conceal themselves and lie in ambuscade for their prey,
and sometimes run after it to a short distance; the second, those
which are constantly roaming about in every direction in search of
it, and seize it by open violence. The former Walckenaer, in his
admirable work on spiders, has designated by the name of _Vagrants_,
the latter by that of _Hunters_; terming those already mentioned
which spin webs and nets, _Sedentaries_: if to these you add the
_Swimmers_, or those species which catch their prey in the water, you
will have an idea of the general manners of the whole race of spiders.
The artifices of that tribe which Walckenaer has named vagrants are
various and singular. _Clubiona holosericea_ and many other species
conceal themselves in a little cell formed of the rolled-up leaf of a
plant, and thence dart upon any insect which chances to pass; while
_C. atrox_ and its affinities select for their place of ambush a hole
in a wall, or lurk behind a stone, or in the bark of a tree. _Aranea
calycina_, L. more ingeniously places herself at the bottom of the
calyx of a dead flower, and pounces upon the unwary flies that come
in search of honey; and _A. arundinacea_ buries herself in the thick
panicle of a reed, and seizes the luckless visitors enticed to rest
upon her silvery concealment. Many of this tribe at times quit their
habitations, and by various stratagems contrive to come within reach of
their prey, as by pretending to be dead, hiding themselves behind any
slight projection, &c. A white species I have often observed squatted
in the blossom of the hawthorn or on the flowers of umbelliferous
plants, and is thus effectually concealed by the similarity of colour.
Foremost amongst the spiders comprehended by Walckenaer under the
general name of hunters, which search after and openly seize their
prey, must be enumerated the monstrous _Mygale avicularia_, at least
two inches long, which takes up its abode in the woods of South
America, and has been reputed to seize and devour even small birds;
but this is wholly denied by Langsdorf, who declares that it eats only
insects[753]. This species, as well as another tropical one, _Thomisus
venatorius_, the European _Cteniza cementaria_, and many others,
construct in the ground very singular cylindrical cavities, and therein
carry and devour their prey. These, being rather the habitations of
insects than snares, I shall describe in a subsequent letter. _Lycosa
saccata_, the species whose affection for its young I have before
detailed, and not a few others of the same family, common in this
country, in like manner seize their prey openly, and when caught
carry it to little inartificial cavities under stones. _Dolomedes
fimbriatus_ hunts along the margins of pools; and _Lycosa piratica_ and
its congeners not only chase their prey in the same situation, but,
venturing to skate upon the surface of the water itself,
"... bathe unwet their oily forms, and dwell
With feet repulsive on the dimpling well."
The Rev. R. Sheppard has often noticed in the fen ditches of Norfolk
a very large spider which actually forms a _raft_ for the purpose of
obtaining its prey with more facility. Keeping its station upon a
ball of weeds about three inches in diameter, probably held together
by slight silken cords, it is wafted along the surface of the water
upon this floating island, which it quits the moment it sees a
drowning insect,--not, as you may conceive, for the sake of applying
to it the process of the Humane Society, but of hastening its exit by
a more speedy engine of destruction. The booty thus seized it devours
at leisure upon its raft, under which it retires when alarmed by any
danger.
The last of the tribe of hunters that it is necessary to
particularize, are those which, like the tigers amongst the larger
animals, seize their victims by leaping upon them. To this division
belongs a very pretty small banded species, _Salticus scenicus_,
which in summer may be seen running on every wall.
To Walckenaer's _swimmers_, the last of his grand tribes of spiders,
including _Argyroneta aquatica_, &c., the first line of the above
quotation from Dr. Darwin is particularly applicable; for these
actually seize their food by diving under the water, their bodies
being kept unwet by a coating of air which constantly surrounds
them.--Thus one single race of insects exemplify in miniature almost
all the modes of obtaining food which prevail amongst predaceous
quadrupeds--the audacious attack of the lion; the wily spring of
the tiger; the sedentary cunning of the lynx; and the amphibious
dexterity of the otter.
This general view of the stratagems by which the spider tribe obtain
their food, imperfect as it is, will, I trust, have interested you
sufficiently to drive away the associations of disgust with which
you, like almost every one else, have probably been accustomed to
regard these insects. Instead of considering them as repulsive
compounds of cruelty and ferocity, you will henceforward see in their
procedures only the ingenious contrivance of patient and industrious
hunters, who while obeying the great law of nature in procuring their
sustenance, are actively serviceable to the human race in destroying
noxious insects. You will allow the poet to stigmatize them as
"... cunning and fierce,
Mixture abhorred!"
but you will see that these epithets are in reality as unjustly
applied to them (at least with reference to the mode in which they
procure their necessary subsistence) as to the patient sportsman who
lays snares for the birds that are to serve for the dinner of his
family; and when you hear
"... the fluttering wing
And shriller sound declare extreme distress,"
you will as little think it the part of true mercy to stretch forth
"the helping hospitable hand" to the entrapped fly as to the captive
birds. The spider requires his meal as well as the Indian: and,
however to our weak capacity the great law of creation "eat or be
eaten" may seem cruel or unnecessary, knowing as we do that it is
the ordinance of a beneficent Being, who does all things well, and
that in fact the sum of happiness is greatly augmented by it, no
man, who does not let a morbid sensibility get the better of his
judgement, will, on account of their subjection to this rule, look
upon predaceous animals with abhorrence.
* * * * *
One more instance of the stratagems of insects in procuring their prey
shall conclude this letter. Other examples might be adduced, but the
enumeration would be tedious. This, from an order of insects widely
differing from that which includes the race of spiders, is perhaps more
curious and interesting than any of those hitherto recited. The insect
to which I allude, an inhabitant of the south of Europe, is the larva
of a species of ant-lion (_Myrmeleon_), so called from its singular
manners in this state. It belongs to a genus between the dragon-fly and
the Hemerobius. When full grown its length is about half an inch: in
shape it has a slight resemblance to a wood-louse, but the outline of
the body is more triangular, the anterior part being considerably wider
than the posterior: it has six legs, and the mouth is furnished with
a forceps consisting of two incurved jaws, which give it a formidable
appearance[754]. If we looked only at its external conformation and
habits, we should be apt to conclude it one of the most helpless
animals in the creation. Its sole food is the juices of other insects,
particularly ants, but at the first view it seems impossible that
it should ever secure a single meal. Not only is its pace slow, but
it can walk in no other direction than _backwards_; you may judge,
therefore, what would be such a hunter's chance of seizing an active
ant. Nor would a stationary posture be more favourable; for its grim
aspect would infallibly impress upon all wanderers the prudence of
keeping at a respectful distance. What then is to become of our poor
ant-lion? In its appetite it is a perfect epicure, never, however
great may be its hunger, deigning to taste of a carcase unless it has
previously had the enjoyment of killing it; and then extracting only
the finer juices. In what possible way can it contrive to supply such a
succession of delicacies, when its ordinary habits seem to unfit it for
obtaining even the coarsest provision? You shall hear. It accomplishes
by artifice what all its open efforts would have been unequal to. It
digs in loose sand a conical pit, in the bottom of which it conceals
itself, and there seizes upon the insects which, chancing to stumble
over the margin, are precipitated down the sides to the centre. "How
wonderful!" you exclaim: but you will be still more surprised when I
have described the whole process by which it excavates its trap, and
the ingenious contrivances to which it has recourse.
Its first concern is to find a soil of loose dry sand, in the
neighbourhood of which, indeed, its provident mother has previously
taken care to place it, and in a sheltered spot near an old wall,
or at the foot of a tree. This is necessary on two accounts: the
prey most acceptable to it abounds there, and no other soil would
suit for the construction of its snare. Its next step is to trace in
the sand a circle, which, like the furrow with which Romulus marked
out the limits of his new city, is to determine the extent of its
future abode. This being done, it proceeds to excavate the cavity by
throwing out the sand in a mode not less singular than effective.
Placing itself in the inside of the circle which it has traced, it
thrusts the hind part of its body under the sand, and with one of
its fore-legs, serving as a shovel, it charges its flat and square
head with a load, which it immediately throws over the outside of
the circle with a jerk strong enough to carry it to the distance of
several inches. This little manœuvre is executed with surprising
promptitude and address. A gardener does not operate so quickly or
so well with his spade and his foot, as the ant-lion with its head
and leg.--Walking backwards, and constantly repeating the process, it
soon arrives at the part of the circle from which it set out. It then
traces a new one, excavates another furrow in a similar manner, and
by a repetition of these operations at length arrives at the centre
of its cavity. One circumstance deserves remark--that it never loads
its head with the sand lying on the _outside_ of the circle, though
it would be as easy to do this with the outward leg, as to remove
the sand within the circle by the inner leg. But it knows that it is
the sand in the interior of the circle only that is to be excavated,
and it therefore constantly uses the leg next the centre. It will
readily occur, however, that to use one leg as a shovel exclusively
throughout the whole of such a toilsome operation, would be extremely
wearisome and painful. For this difficulty our ingenious pioneer has
a resource. After finishing the excavation of one circular furrow,
it traces the next in an opposite direction; and thus alternately
exercises each of its legs without tiring either.
In the course of its labours it frequently meets with small stones:
these it places upon its head one by one, and jerks over the margin
of the pit. But sometimes, when near the bottom, a pebble presents
itself of a size so large that this process is impossible, its head
not being sufficiently broad and strong to bear so great a weight,
and the height being too considerable to admit of projecting so large
a body to the top. A more impatient labourer would despair, but not
so our insect. A new plan is adopted. By a manœuvre, not easily
described, it lifts the stone upon its back, keeps it in a steady
position by an alternate motion of the segments which compose that
part; and carefully walking up the ascent with the burthen, deposits
it on the outside of the margin. When, as occasionally happens, the
stone is round, the labour becomes most difficult and painful. A
spectator watching the motions of the ant-lion feels an inexpressible
interest in its behalf. He sees it with vast exertion elevate the
stone, and begin its arduous retrograde ascent: at every moment the
burthen totters to one side or the other: the adroit porter lifts
up the segments of its back to balance it, and has already nearly
reached the top of the pit, when a stumble or a jolt mocks all its
efforts, and the stone tumbles headlong to the bottom. Mortified, but
not despairing, the ant-lion returns to the charge; again replaces
the stone, on its back; again ascends the side, and artfully avails
himself, for a road, of the channel formed by the falling stone,
against the sides of which he can support his load. This time
possibly he succeeds; or it may be, as is often the case, the stone
again rolls down. When thus unfortunate, our little Sisyphus has
been seen six times patiently to renew his attempt, and was at last,
as such heroic resolution deserved, successful. It is only after a
series of trials have demonstrated the impossibility of succeeding
that our engineer yields to fate, and, quitting his half-excavated
pit, begins the formation of another.