LETTER XIII.

_FOOD OF INSECTS CONTINUED._

STRATAGEMS EMPLOYED IN PROCURING IT.

The _stratagems_ of insects in obtaining their food are now to engage our attention. I shall not dwell on those inartificial modes of surprising their prey, of which examples may be found amongst almost every order of insects, such as watching behind a leaf or other object affording concealment until its approach; but shall proceed to describe the various artifices of the race of spiders, of which there are several hundred distinct species differing essentially from each other both in characters and manners.

Many of these are constantly under our eyes; and were it not that we are accustomed to neglect what is the subject of daily occurrence, we should never behold a spider's web without astonishment. What, if we had not witnessed it, would seem more incredible than that any animal should spin threads; weave these threads into nets more admirable than ever fowler or fisherman fabricated; suspend them with the nicest judgement in the place most abounding in the wished-for prey; and there concealed watch patiently its approach? In this case, as in so many others, we neglect actions in minute animals, which in the larger would excite our endless admiration. How would the world crowd to see a fox which should spin ropes, weave them into an accurately-meshed net, and extend this net between two trees for the purpose of entangling a flight of birds? Or should we think we had ever expressed sufficient wonder at seeing a fish which obtained its prey by a similar contrivance? Yet there would, in reality, be nothing more marvellous in their procedures than in those of spiders, which, indeed, the minuteness of the agent renders more wonderful.

All spiders do not spin webs. A considerable number adopt other means for catching insects. Of these I shall speak hereafter. At present I shall endeavour to give you a clear idea of the operations of the _weavers_, explaining successively the instruments by which they spin--the mode of forming their nets, together with the various descriptions of them--and the manner in which they entrap and secure their prey.

The thread spun by spiders is in substance similar to the silk of the silk-worm and other caterpillars, but of a much finer quality. As in them, it proceeds from reservoirs, into which it is secreted in the form of a viscid gum: but in the mode of its extrication is very dissimilar, issuing not from the mouth but the hinder part of the abdomen. If you examine a spider, you will perceive in this part four or six little teat-like protuberances or spinners. These are the machinery through which, by a process more singular than that of rope-spinning, the thread is drawn. Each spinner is furnished with a multitude of tubes, so numerous and so exquisitely fine, that a space often not much bigger than the pointed end of a pin, is furnished, according to Reaumur[735], with a thousand of them. From each of these tubes, consisting of two pieces, the last of which terminates in a point infinitely fine, proceeds a thread of inconceivable tenuity, which, immediately after issuing from it, unites with all the other threads into one. Hence from each spinner proceeds a compound thread; and these four threads, at the distance of about one-tenth of an inch from the apex of the spinners, again unite, and form the thread we are accustomed to see, which the spider uses in forming its web. The threads, however, are not all of the same thickness, for Leeuwenhoek observed that some of the tubes were larger than others, and furnished a larger thread. Thus a spider's thread, even spun by the smallest species, and when so fine that it is almost imperceptible to our senses, is not, as we suppose, a single line, but a rope composed of at least four thousand strands. How astonishing! But to feel all the wonder of this fact we must follow Leeuwenhoek in one of his calculations on the subject. This renowned microscopic observer found by an accurate estimation that the threads of the minutest spiders, some of which are not larger than a grain of sand, are so fine that four millions of them would not equal in thickness one of the hairs of his beard. Of such tenuity it is utterly beyond the power of the imagination to conceive: the very idea overwhelms our faculties, and humbles us under a sense of their imperfection.--Of the probable accuracy of this calculation you may any day in summer convince yourself, by taking one of the large field spiders (_Epeira Diadema_), and after pressing its abdomen against a leaf or other substance, so as to attach the threads to the surface--the same preliminary step which the spider adopts in spinning--drawing it gradually to a small distance. You will plainly perceive that the proper thread of the spider is formed of four smaller threads, and these again of threads so fine and numerous, that there cannot be fewer than a thousand issue from each spinner; and if you pursue your researches with the microscope, you will find that precisely the same takes place in the minutest species that spins.--You will inquire what can be the end of machinery so complex? One probable reason is, that it was necessary for drying the gum sufficiently to form a tenacious line, that an extensive surface should be exposed to the air; which is admirably effected by dividing it at its exit from the abdomen into such numerous threads. But the chief cause, perhaps, is the occasion (hereafter to be adverted to) which the spider sometimes has to employ its threads in their finer and unconnected state before they unite to form a single one.--The spider is gifted by her Creator with the power of closing the orifices of the spinners at pleasure, and can thus, in dropping from a height by her line, stop her progress at any point of her descent: and, according to Lister[736], she is also able to retract her threads within the abdomen; but this is doubted, and with apparent reason, by De Geer[737].

The only other instruments employed by the spider in weaving are her feet, with the claws of which she usually guides, or keeps separated into two or more, the line from behind; and in many species these are admirably adapted for the purpose, two of them being furnished underneath with teeth like those of a comb, by means of which the threads are kept asunder. But another instrument was wanting. The spider in ascending the line by which she has dropped herself from an eminence, winds up the superfluous cord into a ball. In performing this the pectinated claws would not have been suitable. She is therefore furnished with a _third_ claw between the other two[738], and is thus provided for every occasion.

The situations in which spiders place their nets are as various as their construction. Some prefer the open air, and suspend them in the midst of shrubs or plants most frequented by flies and other small insects, fixing them in a horizontal, a vertical, or an oblique direction. Others select the corners of windows and of rooms, where prey always abounds; while many establish themselves in stables and neglected out-houses, and even in cellars and desolate places in which one would scarcely expect a fly to be caught in a month. It is with the operations of these last especially, that we are accustomed to associate the ideas of neglect and desertion by man--associations which both in painting and allegory have been often happily applied. Hogarth, when he wished to produce a speaking picture of neglected charity, clothed the poor's box in one of his pieces with a spider's web: and the Jews, in one of the fables with which they have disfigured the records of holy writ, have not less ingeniously availed themselves of the same idea. They relate that the reason why Saul did not discover David and his men in the cave of Adullam[739] was, that God had sent a spider which had quickly woven a web across the entrance of the cave in which they were concealed; which being observed by Saul, he thought it useless to investigate further a spot bearing such evident proofs of the absence of any human being[740].

The most incurious observer must have remarked the great difference which exists in the construction of spiders' webs. Those which we most commonly see in houses are of a woven texture similar to fine gauze, and are appropriately termed webs; while those most frequently met with in the fields are composed of a series of concentric circles united by _radii_ diverging from the centre, the threads being remote from each other. These last, which in their simple state, or still more when studded with dew drops, you must have a thousand times admired, are with greater propriety termed _nets_; and the insects which form them proceeding on geometrical principles may be called _geometricians_, while the former can aspire only to the humbler denomination of _weavers_. I shall endeavour to describe the process followed in the construction of both, beginning with the latter.

The weaving spider which is found in houses, having selected some corner for the site of her web, and determined its extent, presses her spinners against one of the walls, and thus glues to it one end of her thread. She then walks along the wall to the opposite side, and there in like manner fastens the other end. This thread, which is to form the outer margin or selvage of her web, and requires strength, she triples or quadruples by a repetition of the operation just described; and from it she draws other threads in various directions, the interstices of which she fills up by running from one to the other, and connecting them by new threads until the whole has assumed the gauze-like texture which we see. Books of natural history, all copying from one another, have described these kinds of web as fabricated of a regular warp and woof, or of parallel longitudinal lines crossed at right angles by transverse ones glued to them at the points of intersection. This, however, is clearly erroneous, as you will see by the slightest examination of a web of this kind, in which no such regularity of texture can be discovered.

The webs just described present merely a simple horizontal surface, but others more frequently seen in outhouses and amongst bushes possess a very artificial appendage. Besides the main web, the spider carries up from its edges and surface a number of single threads often to the height of many feet, joining and crossing each other in various directions. Across these lines, which may be compared to the tackling of a ship, flies seem unable to avoid directing their flight. The certain consequence is, that in striking against these ropes they become slightly entangled, and, in their endeavours to disengage themselves, rarely escape being precipitated into the net spread underneath for their reception, where their doom is inevitable.

But the net is still incomplete. It is necessary that our hunter should conceal her grim visage from the game for which she lies in wait. She does not therefore station herself upon the surface of her net, but in a small silken apartment constructed below it, and completely hidden from view. "In this corner," to use the quaint translation of Pliny by Philemon Holland, Doctor in Physic[741], "with what subtiltie doth she retire making semblance as though she meant nothing less than that she doth, and as if she went about some other business! nay, how close lieth she, that it is impossible to see whether any one be within or no!" But thus removed to a distance from her net and entirely out of sight of it, how is she to know when her prey is entrapped? For this difficulty our ingenious weaver has provided. She has taken care to spin several threads from the edge of the net to that of her hole, which at once inform her by their vibrations of the capture of a fly, and serve as a bridge on which in an instant she can run to secure it.

You will readily conceive that the _geometrical_ spiders, in forming their concentric circled nets, follow a process very different from that just described, than which indeed it is in many respects more curious. As the net is usually fixed in a perpendicular or somewhat oblique direction, in an opening between the leaves of some shrub or plant, it is obvious that round its whole extent will be required lines to which can be attached those ends of the _radii_ that are furthest from the centre. Accordingly the construction of these exterior lines is the spider's first operation. She seems careless about the shape of the area which they inclose, well aware that she can as readily inscribe a circle in a triangle as in a square, and in this respect she is guided by the distance or proximity of the points to which she can attach them. She spares no pains, however, to strengthen and keep them in a proper degree of tension. With the former view she composes each line of five or six or even more threads glued together; and with the latter she fixes to them from different points a numerous and intricate apparatus of smaller threads. Having thus completed the foundations of her snare[742], she proceeds to fill up the outline. Attaching a thread to one of the main lines, she walks along it, guiding it with one of her hind feet that it may not touch in any part and be prematurely glued, and crosses over to the opposite side, where by applying her spinners she firmly fixes it. To the middle of this diagonal thread, which is to form the centre of her net, she fixes a second, which in like manner she conveys and fastens to another part of the lines encircling the area. Her work now proceeds rapidly. During the preliminary operations she sometimes rests, as though her plan required meditation. But no sooner are the marginal lines of her net firmly stretched, and two or three radii spun from its centre, than she continues her labour so quickly and unremittingly that the eye can scarcely follow her progress. The radii to the number of about twenty, giving the net the appearance of a wheel, are speedily finished. She then proceeds to the centre, quickly turns herself round, and pulls each thread with her feet to ascertain its strength, breaking any one that seems defective and replacing it by another. Next, she glues immediately round the centre five or six small concentric circles, distant about half a line from each other, and then four or five larger ones, each separated by a space of half an inch or more. These last serve as a sort of temporary scaffolding to walk over, and to keep the radii properly stretched while she glues to them the concentric circles that are to remain, which she now proceeds to construct. Placing herself at the circumference, and fastening her thread to the end of one of the radii, she walks up that one, towards the centre, to such a distance as to draw the thread from her body of a sufficient length to reach to the next. Then stepping across and conducting the thread with one of her hind feet, she glues it with her spinners to the point in the adjoining radius to which it is to be fixed. This process she repeats until she has filled up nearly the whole space from the circumference to the centre with concentric circles distant from each other about two lines. She always, however, leaves a vacant interval around the smallest first spun circles that are nearest to the centre, but for what end I am unable to conjecture. Lastly, she runs to the centre and bites away the small cotton-like tuft that united all the radii, which being now held together by the circular threads have thus probably their elasticity increased; and in the circular opening resulting from this procedure she takes her station and watches for her prey.

In the above description, which is from my own observations, I have supposed the spider to fix the first and main line of her net to points from one of which she could readily climb to the other, dragging it after her; and many of these nets are placed in situations where this is very practicable. They are frequently, however, stretched in places where it is quite impossible for the spider thus to convey her main line--between the branches of lofty trees having no connection with each other; between two distinct and elevated buildings; and even between plants growing in water. Here then a difficulty occurs. How does the spider contrive to extend her main line, which is often many feet in length, across inaccessible openings of this description?

With the view of deciding this question, to which I could find no very satisfactory answer in books, I made an experiment, for the idea of which I am indebted to a similar one recorded by Mr. Knight[743], who informs us that if a spider be placed upon an upright stick having its bottom immersed in water, it will, after trying in vain all other modes of escape, dart out numerous fine threads so light as to float in the air, some one of which attaching itself to a neighbouring object furnishes a bridge for its escape. It was clear that if this mode is pursued by the geometric spiders, it would go considerably towards furnishing a solution of the difficulty in question. I accordingly placed the large field spider (_Epeira Diadema_) upon a stick about a foot long, set upright in a vessel containing water. After fastening its thread (as all spiders do before they move) at the top of the stick, it crept down the side until it felt the water with its fore feet, which seem to serve as antennæ: it then immediately swung itself from the stick (which was slightly bent) and climbed up by the thread to the top. This it repeated perhaps a score times, sometimes creeping down a different part of the stick, but more frequently down the very side it had so often traversed in vain. Wearied with this sameness in its operations, I left the room for some hours. On my return I was surprised to find my prisoner escaped, and not a little pleased to discover, on further examination, a thread extended from the top of the stick to a cabinet seven or eight inches distant, which thread had doubtless served as its bridge. Eager to witness the process by which the line was constructed, I replaced the spider in its former position. After frequently creeping down and mounting up again as before, at length it let itself drop from the top of the stick, not as before by a single thread, but by _two_, each distant from the other about the twelfth of an inch, guided as usual by one of its hind feet, and one apparently smaller than the other. When it had suffered itself to descend nearly to the surface of the water, it stopped short, and, by some means which I could not distinctly see, broke off close to the spinners the smallest thread, which still adhering by the other end to the top of the stick floated in the air, and was so light as to be carried about by the slightest breath. On approaching a pencil to the loose end of this line, it did not adhere from mere contact. I therefore twisted it once or twice round the pencil, and then drew it tight. The spider, which had previously climbed to the top of the stick, immediately pulled at it with one of its feet, and, finding it sufficiently tense, crept along it, strengthening it as it proceeded by another thread, and thus reached the pencil[744].

That this therefore is one mode by which the geometric spiders convey the main line of their nets between distant objects, there can be no doubt, but that it is the _only_ one is not so clear. If the position of the main line be thus determined by the accidental influence of the wind, we might expect to see these nets arranged with great irregularity, and crossing each other in every direction; yet it is the fact, that however closely crowded they may be, they constantly appear to be placed not by accident but design, commonly running parallel with each other at right angles with the points of support, and never interfering. Another objection too presents itself. From the experiment related, it is clear that the main line of the net can never be longer than the height of the object from which the spider dropped in forming it. But it is no uncommon thing to see nets in which these lines are a yard or two long, fastened to twigs of grass not a foot in height, and yet separated by obstacles effectually precluding the possibility of the spiders having _dragged_ the lines from one to the other. Here therefore some other process must have been used.

Both these difficulties would be removed by adopting the explanation 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.

When all obstacles are overcome, and the pit is finished, it presents itself as a conical hole rather more than two inches deep, gradually contracting to a point at the bottom, and about three inches wide at the top[755]. The ant-lion now takes its station at the bottom of the pit, and, that its gruff appearance may not scare the passengers which approach its den, covers itself with sand all except the points of its expanded forceps. It is not long before an ant on its travels, fearing no harm, steps upon the margin of the pit, either accidentally or for the purpose of exploring the depth below. Alas! its curiosity is dearly gratified. The faithless sand slides from under its feet; its struggles but hasten its descent; and it is precipitated headlong into the jaws of the concealed devourer. Sometimes, however, it chances that the ant is able to stop itself midway, and with all haste scrambles up again. No sooner does the ant-lion perceive this, (for, being furnished with six eyes on each side of his head, he is sufficiently sharp-sighted,) than, shaking off his inactivity, he hastily shovels loads of sand upon his head, and vigorously throws them up in quick succession upon the escaping insect, which, attacked by such a heavy shower from below and treading on so unstable a path, is almost inevitably carried to the bottom. The instant his victim is fairly within reach, the ant-lion seizes him between his jaws, which are admirable instruments, at the same time hooked for holding, and hollow, furnished with a lateral piston, for sucking, and at his leisure extracting all the juices of the body, regales upon formic acid. The dry carcase he subsequently jerks out of his den, that it may not encumber him in his future contests, or betray the "horrid secrets of his prison-house:" and if the sides of the pit have received any damage, he leaves his concealment for awhile to repair it: which having done, he resumes his station.

In this manner in its larva state this insect lives nearly two years, during all which time it receives no food but what has been caught through the artifice above described. Though all living insects, for I have fed it with flies, are equally acceptable to it, as the winged tribe can easily take flight from its pit should they chance to fall into it, its prey consists chiefly of apterous species, of which ants form by far the largest portion, with occasionally an unwary spider or wood-louse. When the full period of its growth is attained it retires under the sand; spins with its anus a silken cocoon; remains a chrysalis a few weeks; and then breaks forth a four-winged insect resembling, as before observed, the dragon-fly both in appearance and manners, and preying in like manner on moths, butterflies, and other insects[756].

The larva of _Myrmeleon Formicaleo_ is not the only insect which avails itself of a trap for obtaining its prey. A plan in most respects similar is adopted by that of a fly (_Leptis Vermileo_) in form somewhat resembling the common flesh maggot. This also digs a funnel-shaped cavity in loose earth or sand, but deeper in proportion to its width than that of _M. Formicaleo_, and excavated not by regular circles, but by throwing out the earth obliquely on all sides. When its trap is finished, it stretches itself near the bottom, remaining stiff and without motion like a piece of wood, and the last segment bent at an angle with the rest, so as to form a strong point of support in the struggles which it often necessarily has with vigorous prey. The moment an insect falls into the pitfall, the larva writhes itself round it like a serpent, transfixes it with its mandibles, and sucks its juices at its ease. If the insect escapes, the larva casts above it jets of sand with surprising rapidity[757].

I am, &c.

FOOTNOTES:

[735] Reaum. _Mem. de l'Acad. de Paris_, An. 1713.211.--De Geer, vii. 187. See also Hoole's _Leeuwenhoek_, i. 41.--_t._ 2. _f._ 20-22. Leeuwenhoek examined a spinner that was not so big as a common grain of sand, and the number of tubes issuing from it was more than a hundred. He affirms that, besides the larger spinners, in the space between them there are four smaller ones, each furnished with organs for spinning threads, but smaller and fewer in number. Latreille speaks only of a thousand spinners from each teat, and of six thousand threads from the whole--but he does not enter further into the subject. _Nouv. Dict. d'Hist. Nat._ ii. 278.

[736] _Hist. Anim. Ang._ p. 8.

[737] De Geer, vii. 189.

[738] Leeuw. _Opusc._ iii. 317. f. 1.

[739] 1 Sam. xxiv. 4.

[740] Lesser, _L._ ii. 291.

[741] L. xi. c. 24.

[742] I am not certain whether the garden spider does not more frequently form one or two of the principal radii of the net, before she spins the exterior lines.

[743] _Treatise on the Apple and Pear_, p. 97.

[744] Some time after making this experiment I stumbled upon a passage in Redi (_De Insectis_, p. 119.) from which it appears that Blancanus, in his _Commentaries upon Aristotle_, has related a series of observations which led him to precisely the same result. Lehmann, too, in a paper in the _Transactions of the Society of Naturalists at Berlin_ (translated in the _Philosophical Magazine_, xi. 323.) has given an explanation somewhat similar of the operations of this very spider, but I am inclined to think erroneous in some particulars. He describes it as emitting _numerous_ floating threads at the _commencement_ of its descent. That he is mistaken in supposing these threads to be more than one, is proved by the fact which I have observed--that even that one sometimes breaks by the weight of the spider. How then could an insect almost as big as a gooseberry be supported by a line of the tenuity here attributed to it?

[745] _An._ vii. _Vindemiaire_. Translated in _Phil. Mag._ ii. 275.

[746] _Hist. Anim. Ang._ p. 7.

[747] Plin. _Hist. Nat._ l. xi. c. 17.

[748] May not the spinners mentioned by Leeuwenhoek (see above p. 404, note) be peculiar to the retiary spiders, and furnish this viscid thread?

[749] Brez, _La Flore des Insectophiles_, 129.

[750] Lister, _Hist. Anim. Ang._ 32, tit. 4.

[751] _Phil. Tr._ 1668, p. 792.

[752] _Embassy to China_, i. 343.

[753] _Bemerkungen auf einer Reise um die Welt._ i. 63.

[754] PLATE XIX. FIG. 8.

[755] The nests of this animal which I saw at Fontainebleau (in the pit producing the fossil named after that place) were scarcely half the dimensions here given, but they might probably be younger insects. I kept one in a box of sand several days, in which it regularly formed its pit, whenever obliterated by shaking. The bottom of the box unfortunately came out as I was upon my return to England, and the animal was killed.

[756] Reaum. vi. 333-78. Bonnet, ii. 380.

[757] Bonnet, ix. 414. De Geer, vi. 168. _t._ 10.