musical lovers among spiders and scorpions—colour among spiders, and its uses—the spiders’ dance of death—spiders and conjugal bliss—how pairing is accomplished—scorpions in love—musical crabs—quarrelsome fiddler-crabs—crabs and courtship in the deep sea—amazons among prawns—brine-shrimps and water-fleas—“natural” v. “sexual” selection.
it is a curious and significant fact that in the most brilliantly coloured of the invertebrates—the butterflies and moths—” courtship” in the sense of “wooing” is extremely rarely met with; and this is quite contrary to what the sexual selection theory of darwin demands, for, according to this, the colours are the result of that selection. on the other hand, spiders, which are for the most part dull-coloured creatures, and the scorpions, which are also dull-coloured, are commonly extraordinarily demonstrative during the early stages of “mate-hunger.” some practise the form of instrumental music known as “stridulation,” others dance and indulge in other forms of posturing.
in the spiders the stridulating apparatus is formed either between the limb-bearing portions of the body, or “cephalothorax,” and the abdomen; between the 237palps or leg-like feelers, and the jaws; or between these feelers and the front legs. but the construction is similar in all. in some spiders the abdomen bears a horny collar, which is toothed, and these teeth, as the abdomen is raised and depressed, scrape against a number of delicate ridges on the thorax, or “chest,” which form a surface recalling that of a file. the grating of these opposing surfaces against one another produces shrill rasping or chirping sounds, which, in some cases at any rate, seem to be designed to inform the female of the presence of a suitor. those who will, may examine this strange instrument for themselves if they will take the trouble to seek for it in one of our commonest english spiders (steatoda bipunctata). that it serves as a sexual excitant, or as an aid to mate-hunting, is indicated by the fact that it is found in males only, or in a very rudimentary condition in the female. there is a large spider in assam (chilobrachys stridulatus) which produces a sound like the drawing of the back of a knife along the edge of a strong comb; and there are others which, by the friction of the feelers against the jaws, produce sounds like the buzzing of bees. one of the wolf-spiders (lycosa kochy) is known as the “purring” or “drumming” spider from its custom, at mating-time, of rapidly drumming on dead leaves with its feelers. it is a wood-haunting species, and runs hither and thither over the ground as if searching for something, and pausing frequently to “purr.” this singular method of producing sound recalls that of the drumming of woodpeckers on the hollow branches of trees, and similarly is produced without any special mechanism.
that the scorpions should possess similar stridulating organs is only what we should expect, having regard to 238their kinship with the spiders. in the great rock scorpions of india and africa the stridulating apparatus lies between the basal segment of the pincers and that of the first pair of legs, and consists of a set of tubercles and a cluster of curved, hair-tipped spines. during moments of excitement the pincers are waved up and down so that the spinules scrape against the tubercles, emitting a rustling sound, which has been compared to that produced by rubbing a stiff tooth-brush with one’s finger-nails. in the south african opisthophthalmus the mechanism differs, consisting of leaf-like hairs placed on the inner surface of the jaws. but since both sexes possess these strange sound-producing mechanisms it has been suggested that their main, if not their only purpose, is to serve as a warning to enemies to keep their distance. some of the great bird-eating spiders (aviculariid?) produce a kind of whistle; others, sounds like the dropping of shot upon a plate.
these stridulating contrivances present some curious and puzzling features. in the first place the sounds they produce are never loud to human ears; therein they differ from the shrill piercing sounds produced by like mechanism by the crickets and grasshoppers, though even with some of these the notes are, to us, inaudible. in the second, it has been suggested that where both sexes possess a stridulating apparatus its purpose is solely to warn off enemies, and this because the performers have no sense of hearing, and are thus, we presume, unaware of the sounds they produce. there is something unsatisfactory about this line of argument. there seems to be no evidence either that the sounds produced are loud enough to terrify an enemy, or that the performers are really deaf.
239in cases where the males alone stridulate it is always supposed that this “music” serves the purpose of a lure, or acts as an excitant, to the female, even though inaudible to human ears. but there are many people who are unable to hear the shrill squeal of our native bats. yet no one doubts but that all bats hear it. the argument as to the absence of any sense of hearing in certain spiders is based on their failure to respond to the vibrations of a tuning-fork, but this evidence is not conclusive. neither is it safe to infer that the presence of stridulating organs in the adult and immature stages of both sexes, in some species, precludes their recognition as secondary sexual characters. they may serve the double purpose of sexual excitants and terrifying enemies, their motive being expressed by the quality of the sound as certainly as the timbre of the human voice may express rage or pleasure.
neither spiders nor scorpions exhibit any very striking secondary sexual characters. as a rule the female is the larger, often strikingly so. bright colours are rare, and are met with only among the spiders, wherein sometimes the male, sometimes the female, is the more resplendent; where bright colours—apple-green, red and yellow—do occur, they seem rather to be of the type known as anti-cryptic, or aggressive resemblance colours. that is to say, they are hues developed to deceive prey by reason of the likeness they afford the wearer to its surroundings. thus, for example, one of our native spiders (tibellus oblongus) is straw-coloured, and has an elongated body, which is therefore seen with difficulty amid dry grass and rushes which are the haunts of the species. misumena vatia, one of the crab-spiders, resembles the flowers on which it is accustomed to lurk for its prey. it is of a 240variable hue, commonly yellow or pink, and a favoured lurking-place is near the blooms of the great mullein (verbascum thapsus), where it seizes upon bees coming for honey. exotic relatives of this species afford far more striking illustrations of this kind. one has a pink, three-lobed body which bears a striking likeness to a withered flower, and it exhales a sweet odour of jasmine. insects attracted by the smell are thus readily pounced upon. dr. trimen, of cape town, describes a rose-red species which exactly matches an oleander flower, and to complete the deception the abdomen is marked with white. the same observer, approaching a bush of the yellow-flowered senecio pubigera, noticed that two of the numerous butterflies settled upon it did not fly away with their companions. each of these he found to be in the clutches of a spider whose remarkable resemblance to the flower lay not only in its colour, but in the attitude it assumed. “holding on to the flower-stalk by the two hinder pairs of legs, it extended the two long front pairs upwards and laterally. in this position it was scarcely possible to believe that it was not a flower seen in profile, the rounded abdomen representing the central mass of florets, and the extended legs the ray florets; while to complete the illusion the femora of the front pair of legs, addressed to the thorax, have each a longitudinal red stripe which represents the ferruginous stripe on the sepals of the flower.” but more remarkable still is the case cited by my friend dr. h. o. forbes. this came under his notice while butterfly hunting in java. the butterflies of the family hesperid? have a habit of settling on the excreta of birds. forbes noticed one on a leaf apparently enjoying a feast. creeping up, he seized hold of this victim 241of a depraved taste and found it mysteriously held down. on further examination of this “excreta” he found that it was really a spider! later, when in sumatra, the same species once more in like manner deceived him. the deception is more than usually remarkable, for it is not due to the coloration of the body, but to what may almost be described as a diabolically ingenious display of intelligence. for the creature weaves upon a leaf a small white patch of web exactly resembling the fluid excrement of a bird sliding down the smooth surface of the leaf. having completed this, the weaver lies on its back in the middle of the web holding on by the spines with which the legs are furnished. it then awaits its victim with the disengaged portions of the legs ready to close in a deadly embrace the moment the lure has done its work. though somewhat in the nature of a digression, these facts show that colour often plays a vital part in well-being; though in the matter of courtship its r?le has probably been overestimated. colour as an aid to “mate hunting “probably nowhere plays so important a part as was at one time believed. the warblers among the birds, and the spiders among more lowly animals, seem to demonstrate this fact.
the actual mating of spiders, the act of coition, is peculiar, and demands notice, for the orgasm is not accomplished at the moment of the ejection of the sexual products. the male discharges the seminal fluid upon a small web woven for the purpose, and the liberated spermatozoa are then sucked up into a tube—the receptaculum seminis—which lies coiled up within a hollow bulb attached to the base of the last joint of the leg-like feeler, or “pedipalp” at the base of the head. the precious fluid is there stored and retained until the moment arrives when these palps can be thrust into die 242genital aperture of the female, and their contents discharged for the second and last time. this is the critical moment of the spider’s life, and it is noteworthy that it should occur now, instead of at the moment of the discharge from the body. the ejection from the palpal organ is effected by means of a fibro-elastic bag, in its normal, collapsed, state spirally disposed round the base of the bulb which contains the sperm tube. immediately preceding copulation this elastic bag or “h?matodocha” becomes turgid with blood, and it is probably the pressure thus exerted on its base which affords the final fury of desire without which, indeed, one might well imagine the necessary courage for copulation would never be raised, at any rate, in the case of some species.
strange as these facts are, the nice adjustment of the instincts for their effectual performance is, by comparison, stranger still. by what subtle sense is the male spider informed of the importance of the fertilizing fluid which escapes his body? what prompts him before its escape to prepare a web for its reception? what prompts him after its deposition to collect it within the palp till it shall be needed? the least defect in the instincts appertaining to these vitally important acts would mean the extinction of the race. we cannot suppose that the nature of their performance is in any way realized by the performer, and this makes their orderly execution the more wonderful.
plate 34.
male astia displaying before the less brilliant female.
from drawings, t. carreras, in “marvels of the universe.”
male icius displaying.
the “courtship” of the male spider takes the form of a “display” recalling that of birds. he commonly ends in being eaten by his mate.
[face page 242.
our knowledge of spiders under the afflatus of sexual desire has been immensely increased by the long and patient observations of mr. and mrs. peckham. the fact that their investigations were carried on with captive specimens, and therefore under artificial conditions both as to environment and the number of individuals placed 243together at one time, must not be lost sight of; nor must we forget that they worked under the firm conviction that the sexual selection theory of choice by the females was an indisputable fact. wherever colour was present they looked for, and saw, evidence that the female appreciated such hues, though from their observations it would seem that dull-coloured species behaved as though they were suffused with resplendent hues. in the course of their studies the courtship of several species was investigated, but a summary of their results is all that can be given here. saitis pulex formed the subject of one of their experiments. a male was placed in a box containing a mature female. “he saw her as she stood perfectly still, twelve inches away; the glance seemed to excite him and he moved towards her; when some four inches from her he stood still, and then began the most remarkable performance that an amorous male could offer to an admiring female. she eyed him eagerly, changing her position from time to time so that he might be always in view. he, raising his whole body on one side by straightening out the legs, and lowering it on the other by folding the first two pairs of legs up and under, leans so far over as to be in danger of losing his balance, which he only maintains by sidling rapidly towards the lowered side. the palpus, too, on this side was turned back to correspond to the direction of the legs nearest to it. he moved in a semicircle for about two inches, and then instantly reversed the position of the legs and circled in the opposite direction, gradually approaching nearer and nearer to the female. now she dashes towards him, while he, raising his first pair of legs, extends them upwards and forwards as if to hold her off, but withal slowly retreats. again and again he 244circles from side to side, she gazing towards him in a softer mood, evidently admiring the grace of his antics. this is repeated until we have counted one hundred and eleven circles made by the ardent little male. now he approaches nearer and nearer, and when almost within reach whirls madly around and around her, she joining and whirling with him in a giddy maze. again he falls back and resumes his semicircular motions with his body tilted over; she, all excitement, lowers her head and raises her body so that it is almost vertical; both draw nearer; she moves slowly under him, he crawling over her head, and the mating is accomplished. after they have paired once the preliminary courtship is not so long. on one occasion a female was the more eager of the two, but this is evidently very exceptional. the female always watches the antics of the male intently, but often refuses him in the end, even after dancing before her for a long time.”
of another species—epiblemum scenicum—they write: “the females seemed to have some difficulty in choosing from among the males, but after a decision has been reached and a male accepted, there appeared to be complete agreement.” a species of the genus iritis, which seems to have baffled identification, was watched for hours under natural conditions as well as in confinement.” a dozen or more males, and about half as many females, were assembled together within the length of one of the rails. the males were rushing hither and thither, dancing opposite now one female, now another; often two males met each other, when a short passage of arms followed. they waved their first legs, sidled back and forth, and then rushed together and clinched, but quickly separated, 245neither being hurt, only to run off in search of fairer foes.”
these most patient observers seem to have been convinced that whenever spiders possess vividly coloured areas on their bodies they are not only conscious of this fact, but desire to make the most of such splendour during the period of love-making. thus they interpret the behaviour of a curiously ant-like spider—synageles picata—which has the first pair of legs especially thickened, flattened on the anterior surface, and of a highly iridescent steel-blue colour. as he approaches the female he pauses “every few moments to rock from side to side, and to bend his brilliant legs so that she may look full at them; ... he could not have chosen a better position than the one he took to make a display.” and similarly they interpret the movements of another species—dendryphantes capitatus—which has a bronze-brown face, rendered conspicuous by snow-white bands. the attitude he assumes when sexually excited is one which seems, to them at any rate, to serve admirably to expose this feature to the watchful female. but he has other charms, and his “antics are repeated for a very long time, often for hours; when at last, the female, either won by his beauty or worn out by his persistence, accepts his addresses.” habrocestum splendens—unhappily these creatures have no names in common speech—possesses an abdomen of a magnificent purplish red, and the attitude which he assumes at courtship they regard as one designed to display this to the full. another case of quite remarkable interest is that of astia vittata, because the males appear to be dimorphic. that is to say, they appear under two quite distinct forms, the one red, like the female; and the other black, with three tufts of hair just behind the head. the attitudes and 246the movements of courtship, it is significant to remark, are entirely different in the two varieties: the black form, assumed to be the later development, “is much the more lively of the two, and whenever the varieties were seen to compete for a female, the black one was successful.”
professor poulton, commenting on this particular case, contends that “it must be admitted that these facts afford the strongest support to the theory of sexual selection.” but do they? a further examination of the facts will probably show that the red “form” is but an immature example, and this being so, the difference in performance and the invariable success of othello is at once accounted for. the fact that the “two forms pass into each other” and that the “tufts only occur in the fully developed niger form” is an additional reason for regarding the red form as immature.
professor poulton remarks: “when the males possess any special adornment they make a point of displaying them as fully as possible.” if this be so it seems to be a very foolhardy proceeding, akin to holding the proverbial “red rag” to a bull: for it is well known that the male spider seeking a mate carries his life in his hands, at any rate in the case of many species. mr. and mrs. peckham observed several instances of this remarkable sequel to love’s embraces. in describing the female of phidippus morsitans they remark that she was “a savage monster. the two males we provided for her had offered her only the merest civilities, when she leaped upon them and killed them.” the first pair of legs in the males of this species possess “special adornments” in the shape of long white hairs, and it was “while one of the males was waving these handsome 247legs over his head that he was seized by his mate and devoured.” again, in the case of a male of phidippus rufus, the display of his “ornaments” was his undoing, for he was “caught and eaten when he insisted upon showing off his fine points too persistently.” thus the females seem to “select” the more resplendent males as much for eating as for mating! the ogre-like habits of the females in this regard, indeed, are almost without parallel in the animal kingdom.
anyone who cares to take the trouble to watch the web of the large garden spider (epeira diademata) may witness one of these connubial tragedies. in this species, the males are conspicuously smaller than the females, and it is possible that this disparity has been brought about by sexual selection, the largest and least active males having been exterminated. in some species the discrepancy in size is most striking, as for example in nephila chrysogaster, the female of which measures two inches in length, the male not more than one-tenth of an inch, and less than one one-thousand-three-hundredth part of her weight.
the males, apparently, fully realize the perils which their amours may lead them into. they haunt the borders of the webs of unmated females, but exhibit a hesitating, irresolute manner. for hours they will linger near her, feeling the silken carpet cautiously with their legs, and apparently trying to ascertain the nature of the welcome likely to be extended to them. the odds are against them: for even if allowed to mate, unless they are extraordinarily agile in slipping away the moment they have attained their object, the chances are they will be slain and eaten!
among some species, however, matters are otherwise: 248for the males of the genus linyphia, for example, are generally to be found living peacefully with their consorts.
more rarely the male weaves a small nuptial tent, into which he partly leads and partly drives the female: though the “driving” would appear to be merely for form’s sake! the habits of the cellar spider (tegenaria parietina), a long-legged species fairly common in the south of england, affords a yet further interesting and instructive contrast with the foregoing accounts. the pairing habits of this species have been studied by many observers, but perhaps the best account is that of mr. f. m. campbell. he found, to begin with, that in this species the tender ties of mating are at any rate rarely violated by the horrible aftermath of cannibalism so common a feature with so many other spiders.
one or two illustrations from mr. campbell’s work must suffice. on one occasion he placed together a male and a female. for four days they took no notice of one another; then the female cast what proved to be her last skin, and within three hours after, the male began to show signs of interest in her presence—which is a fact of some significance, for not till then had she attained maturity. “after a few convulsive twitchings of the legs, the male pressed forwards, moving his palpi”—the leg like “feelers” on each side of the head which form the genital organs (page 241)—“up and down, when, as they touched the palpi of the female, the pair played with these organs like two friendly bees with their antenn?. after a few minutes the female raised herself, leaning a little on her left side, and the male crept forward until his head was under the breast of his mate, while his first pair of legs were resting upon hers. he now 249advanced his right palpus, leaning a little to the left and using the left palpus as part of his support. the right palpus was slightly twisted so as to bring the surface (containing the fertilizing germs) opposite the sexual organs of the female.... he now rapidly raised his palpus up and down for four or more seconds, and with such energy as to compel her to assume a vertical position. he then retired and again approached her, repeating the movements ... occasionally pausing before he withdrew his palpus.... at times he would leave the female for five minutes, and strut with straightened legs round the vase, wagging his abdomen. now and then he would remain perfectly still with the palpus withdrawn, or play with the palpi of the female, while she seemed in a comatose state. he would then renew the union with undiminished vigour, appearing on each occasion less desirous of changing his position. i left them at 12–30 a.m. and returned at 7 a.m. the male was still using his right palpus. i saw no application of the left palpus, but have no doubt that it was employed during the night, as in other cases. i have not observed the pairing ever interrupted by a fresh collection of semen, although there is no reason to think this may not occur. the duration of pairing is long; but i am inclined to think it is more dependent on the difficulty in inserting the palpus than on sexual endurance. the impregnation appeared to take place when the male retained his palpi in front of the bursa copulatrices for about thirty seconds, which was frequently the case.” there are occasions, however, when a very different sequel attends this dalliance. in one instance, for example, mr. campbell placed a pair together, and at once the male began to pay his addresses. “shortly 250afterwards he rapidly applied one of his palpi to the female ... apparently with her consent.” five hours later “he charged her, tore away two legs ... and began to suck one, using the mandibles to hold the limb as a human being would a stick of asparagus.” it is not surprising to find she died an hour afterwards. an examination of her remains brought to light the fact that she was not mature. but this does not apparently explain the ferocity of her partner, for this investigator on two other occasions saw males similarly dismember their spouses an hour or so after impregnation. this horrid feast cannot have been prompted by hunger, for one of these males had, but a few hours previously, eaten a daddy-long-legs and two blow-flies. only twice did this investigator see a female of this species drive away a male, and in each case immediately after union. “on the other hand,” he says, “i have kept an adult pair together from the 22nd of august to the 28th of october, and they lived in perfect amity. the male never ceased paying unrequited attentions except to feed.” it will have been remarked that the behaviour of this species in regard to mating differs conspicuously from the accounts of observations on other species, wherein the aggressive instincts are displayed by the female. mr. campbell, commenting on these facts, remarks that such conduct is just what one would expect from creatures which lead solitary lives, and must have “come to regard weaker forms of animal life as food, or as an inconvenience, if we except its young or its mate when in the act of pairing.” instincts which are habitually practised throughout the greater portion of the life of the species, and on which existence depends, would scarcely be suspended for a longer period than necessary for sexual 251union. spiders frequently eat one another, and such an occurrence after pairing is only curious if considered apart from their habits. when the sexual desire is satisfied, their actions would again be directed by the dominant instinct of destruction.
it is to be noticed that the attack, when made by a female, often immediately follows the sexual union, while in the case where males assume the aggressive it takes place some time afterwards. mr. campbell explains this by the supposition that the action of the female, when satiated, would be precipitated by the threatened and unacceptable continued application of the hard, spiny palpus, while the more lasting desire of the male would have to subside before he became directed by another instinct. by that time, other attractions, if not his wandering disposition, would take him away from the web.
the fact that male spiders are comparatively rare is perhaps explained by the fact that they are very short-lived; they probably die soon after pairing—even if they are not eaten! the snares they spin, it is to be noted, are very imperfect, though curiously enough, when young they make perfect snares on a small scale.
it will have been noticed, in the course of the foregoing descriptions, that spiders display a more or less conspicuous wariness, a cool, deliberate “counting on the cost” in their matrimonial ventures that is often wanting in such matters in the human race. but, then, the risks involved are more patent, more imminent. mr. campbell comments on this intelligent behaviour in the case of the cellar spider, remarking that they measure “each other’s strength when on the same web by the tension and motion of the threads.”
252a word as to the scorpions. these creatures are near relations of the spiders, and in many things resemble them, notably in regard to their ferocity. one does not meet here, however, with the same disparity in size between the sexes, nor are vivid colours ever developed. this, according to some, would be accounted for by the fact that though these creatures possess numerous eyes they are practically blind, and depend for their information as to what is going on around them by their sense of touch, which is excessively delicate. they are morose in disposition and always solitary. it has been said that if two are found under the same stone—a favourite lurking-place—one is engaged in eating the other! nevertheless, they are of abstemious habits, for the naturalist fabre found that from october to march they last, though throughout this time they remain alert, and always ready to resent disturbance. in april they exhibit more activity, though even then they eat but little. but now they begin to wander in search of mates.
fabre’s observations on their mating habits are exceedingly interesting, and they have brought to light some very extraordinary phenomena. his notes were made on the species common in the south of france—buthus occitans. mr. cecil warburton, referring to the distinguished frenchman’s work, quotes the following noteworthy passage in the cambridge natural history: “after some very curious antics, in which the animals stood face to face with raised tails, which they intertwined ... they always indulged in what fabre calls a ‘promenade à deux’ hand in hand, so to speak, the male seizing the chel? of the female with his own and walking backwards, while the female followed, usually without any reluctance. this promenade occupied an 253hour or more, during which the animals turned several times. at length, if in the neighbourhood of a suitable stone, the male would dig a hole, without for a moment entirely quitting his hold of the female, and presently both would disappear into the newly-formed retreat.”
plate 35.
photo by p. h. fabre.
scorpions.
the early stages in the courtship of the scorpions are full of romance. the two prospective partners for life engaging in a kind of waltz, holding each other’s “hands.”
[face page 252.
after the mating, as with the spiders, the male is often devoured by the female. after any combat with an enemy, such as a lycosa or a scolopendra, it seems to be de rigueur to eat the vanquished.
if the mating period in the case of the higher animals rouses the males to the pitch of frenzy, that frenzy is dangerous only to possible rivals. with the more lowly spiders and scorpions ferocity of disposition is a normal feature, and one which can with difficulty be held in check long enough to permit the all-important act of mating to take place. in how far this is accounted for by the extremely deficient senses of sight and hearing, which are such marked features in these animals, it would be difficult to estimate. but that the manner of their display is governed by these deficiencies there can be no doubt. the spider, having a more or less efficient vision at short range, executes more or less elaborate antics in front of the female, designed, as in the case of the birds, to serve as excitants to fan sexual desire, already smouldering, to a flame. with the purblind scorpion the spider-antics are useless; he must proclaim his desire by a pressure of the hand, and by intertwining his tail with that of his prospective mate as they “walk out” together. but scorpions at one time were credited with a very acute sense of hearing; later investigations, however, fail to yield any evidence whatever that they possess this sense, though experiment has proved that 254their sense of touch is excessively delicate and seems to reside in the hairs which are thickly distributed over the legs and body. now, hearing and touch are senses near akin, and the vibrations produced by stridulation may be, and probably are, received by, and interpreted through, the medium of these hairs. for though the scorpion may not respond to sounds made by curious investigators, it may be that they can perceive notes of a low pitch imperceptible to our ears, such as are made by stridulating organs, as in the case of the spiders.
perchance certain comb-like structures known as the “pectines” may play a part in mate-hunting. these are placed on either side of the under-surface of the body between the last two pairs of legs. the fact that they are larger in the male, and sometimes strangely modified in the female, seems to show that they have some function in relation to sex. they also appear to serve as sources of information as to the nature of the ground traversed by the animal, since they are long in species which walk with the body raised high off the ground and short in such as adopt a more grovelling posture. that the scorpions possess but a very limited means of gleaning information of the outer world there can be no doubt. how, then, do they find one another when that insistent desire to mate begins to make itself felt? are the “pectines” their informants through the sense of smell? do the hairs scattered over the body act as sound-collectors responding to the notes emitted by the stridulating organs? these are points on which information is much to be desired.
plate 36.
photo by p. h. fabre.
death of the male scorpion.
but by the time the nuptial rites have been performed the female has thrown off her “sweetness,” and ends by eating her lover!
[face page 254.
plate 37.
photo by paul h. fabre.
the female mantis devouring her mate.
with these insects, as with the spiders and scorpions, the male is often eaten by the female.
our survey of the “arthropoda,” as those limb-bearing jointed animals invested in a horny, or, more exactly, a “chitinous” external skeleton are called has so far 255been confined to such as, during adult life, at least, are land-dwellers. but the aquatic types known as the “crustacea” furnish some extremely interesting facts in regard to the problems of sex. in the first place, they too possess a stridulating apparatus. this is curious, but not surprising, because, although the skeleton of such creatures is of a harder and almost stone-like character, the development of roughened surfaces working in opposition to one another might well have been foretold to occur, at least in some individuals. colonel alcock—a naturalist who has contributed largely to our knowledge of marine animals by his researches in the indian ocean—in his most delightful book “a naturalist in indian seas,” describes what he calls a “musical crab.” this is the great-horned coromandel strand crab (ocypoda macrocera). in both sexes of this remarkable genus he says, “the nippers, or chelipeds, are singularly unequal in size, and in all the species but one there is present on the inner surface of the ‘hand’ of the larger cheliped a transverse row of five teeth, which, when the cheliped is flexed, can be made to play against a ridge or another row of teeth on its ‘arm’ ... much as a man might rub one side of his chest with the palm of the corresponding hand. the whole mechanism, except that it is on a larger scale and has a more finished appearance, is very much like that by means of which crickets and grasshoppers produce their shrill music, and no one has ever doubted that it is used for the same purpose, though very few people have actually heard it in action. i myself ... was beginning to think that the structure must, after all, have some quite other function, when one morning ... on the sandy wastes 256of the godavari delta, i at last, like ancient pistol, heard with ears that which i had been so long waiting for. that is to say, i heard a noise very much like that which an angry squirrel makes, and discovered that it came from a red ocypode crab into whose burrow another individual had trespassed.
“in order to understand the matter it should be known that these crabs ... are gregarious, and that each one has a burrow of its own. though they may be seen marching in battalions across the sand, yet as a rule they stay close to their burrows, methodically searching and sifting the surrounding sand for any food that may have been thrown up by the tide, and flying to their burrows with headlong speed when alarmed. at first sight one does not understand the necessity for so much wariness, and for such a deep system of entrenchment, for the creatures seem to hold undisputed possession of the whole shore; but as a matter of fact they are preyed upon all day long by brahminy kites, and when the jackals come out in the evening, by them. now, although each crab may on ordinary peaceful occasions know its own home, yet when a crowd of them are running for their lives they may sometimes, one would think, act on the devil take the hindmost principle and try to squeeze into the nearest burrow. but as ancient philosophers do report, things may be done upon occasion which it is inexpedient to make a habit of doing, and this seems to be one of those things; for if many crabs made a practice of crowding into one small burrow they would certainly run the risk of being suffocated, if not crushed to death outright. it seems probable, therefore, that it would be advantageous to the species as a whole if the rights of property in burrows were rigidly respected, and if each individual 257member possessed some means of giving notice that its burrow was occupied ... and i think that this consideration gives us a clue to the use of the stridulating mechanism. at any rate, i was often able, after my first accidental discovery, to elicit the sound, by catching one of these crabs and forcing it into a burrow which i knew was already occupied: the intruder would never go far in, but would crouch just inside the mouth of the burrow, and if it were made to travel deeper, then the voice of the rightful owner would be heard in indignant remonstrance from the depths.” another species, the grey ocypode crab (ocypoda ceratophthalmus), possesses a similar instrument, and makes therewith a loud, croaking noise. but it does not often burrow deeply. colonel alcock therefore suggests that in this case it may be used for scaring enemies.
that these curious musical instruments may also be used in mate-hunting seems highly probable. if the stridulation is produced on one occasion to announce the fact that callers are not desired, it may on another signify an equally emphatic invitation to enter, the mood of the occupant being expressed by the character of the sounds emitted. it is significant, at any rate, that there are no external sexual differences in these species; hence the probability that it is by stridulation that the sexes distinguish one another.
this view seems to obtain confirmation from the fact that the crabs of the genus gelasimus, or “fiddler-crabs,” which are near relations of the ocypode crabs, and, like them, live in burrows in large companies, and are exposed to the same enemies, which they avoid in the same way by burrowing, have no stridulating mechanism, but the sexes are strikingly different. this is especially so in the case of the nippers, or chelipeds. these, in the 258female, are slender and much shorter than the legs, being used mainly for feeding. in the adult male one of these “hands” is often twice as big as the body itself! “many uses,” remarks colonel alcock, “have been assigned to this enormous, lop-sided organ: some say that it is used as a stopper to barricade the mouth of the burrow, others that it is a sort of cradle or bridal-couch upon which the female reclines—the male, in this case, literally bestowing his hand upon the female; but from observations of gelasimus annulipes, the species which most frequents the godavari mud-flats, i believe that it primarily serves as a war-club, for the males indulge in interminable tournaments for the hand of the female; and secondarily, for it is of a most beautiful cherry-red colour, as an ornament to attract and delight the latter capricious sex.
“landing one afternoon in march upon a cheerful mud-flat of the godavari sea-face, i was bewildered by the sight of a multitude of small pink objects twinkling in the sun, and always, like will-o’-the-wisps, disappearing as i came near to them, but flashing brightly on ahead as far as the eye could reach. it was not until i stayed perfectly quiet that i discovered that these twinkling gems were the brandished nippers of a host of the males of gelasimus annulipes. by long watching, i found out that the little creatures were waving their nippers with a purpose—the purpose apparently being to attract the attention of an occasional infrequent female, who, uncertain, coy, and hard to please, might be seen unconcernedly sifting the sand at the mouth of her burrow. if this demure little flirt happened to creep near the burrow of one of the males, then that favoured individual became frantic with excitement, dancing round his 259domain on tip-toe and waving his great cherry hand as if demented. then, if another male, burning with jealousy, showed a desire to interfere, the two puny little suitors would make savage back-handed swipes at one another, wielding their cumbrous hands as if they had no weight at all. unfortunately, though i spent many a precious hour on the watch from time to time, i could never see that these combats came to anything; the males seemed always to be in a state of passionate excitement, and the females to be always indifferent and unconcerned; and though the dismembered chelipeds of vanquished males could often be seen lying on the battle-field, i never had the satisfaction of beholding a good stand-up fight, fought out to the sweet end, or a female rewarding a successful champion with her heartless person.”
photos by w. saville-kent.
the “fiddler-crab.”
this “strong right arm” is used in conflicts with rivals for the possession of the females.
plate 38.
the “fiddler-crab” among mangoe roots.
this species is remarkable for the enormous size of the right “arm,” which exceeds that of the body.
[face page 258.
the fascinating tale of colonel alcock’s observations does not end here, however, for he has brought to light some extremely interesting facts in regard to the sexual aspect of crustacean life in the deep sea; information gathered during his exploration work on board the investigatory much of which was done to enlarge our knowledge of the abysses of the ocean where the light of day never penetrates. here, he remarks, the conditions of life might seem to be reduced to a minimum of simplicity, yet evidences are not wanting that, among the higher crustacea, they are complicated, much as they are everywhere else, by the play of the sexual instincts.
in these awful depths, where reigns eternal night, most of the inhabitants, of whatever kind, from fishes downwards, are blind and eyeless, or they possess 260enormous eyes and a purblind vision responding to the only light these regions display, that of phosphorescence, which is generated by so large a number of those creatures which are condemned by fate to live this sunless life.
“it is written,” he remarks, “that the male must exert himself to find a mate, and where sight cannot help him in his search, a kind of blind-man’s buff is the only alternative. in this serious game many deep-sea crustacea, especially those of the shrimp-tribes, trust to the sense of smell, as the greatly developed outer, or olfactory, branch of the first pair of antenn? bears witness. these antenn?, again, seem to be used by the males of some species for catching their partners, and in parapeneus rectacutus ... they are turned into a sort of crook for this purpose. this has long been thought to be their function in the prawns of the oceanic genus sergestes.” in the male of certain other deep-sea prawns, the hind pair of foot-jaws are modified in a way which can only mean that they are used for hooking on to a partner of the opposite sex. in the deep-sea hermit-lobsters of the genus munida the nippers are greatly enlarged, as in many shore-crabs, for the purpose of subjugating rivals and embracing the females; and in all such cases these are much smaller in the female and immature male.
mention of numerous cases has already been made where the female is larger than the male, and is the more pugnacious, and in such cases the females are generally more numerous than the males. some of the deep-sea prawns exhibit the same peculiarity. and in these the sword-like forward prolongation of the head-shield is far larger than in the male. now this rostrum is the most formidable weapon which the prawn possesses, 261so that we may, with tolerable certainty, conclude that the females fight their rivals for the possession of the males, which are, in these species, far less numerous than the females.
among the lower crustacea, such as the “fairy-shrimps,” “brine-shrimps,” the “water-fleas,” and the “copepoda,” which play so important a part in furnishing food for many of the fishes which in turn feed us, secondary sexual characters of an extremely interesting kind are met with. these, however, are never such as appeal to the eye, for the vision in these creatures is but feebly developed. scent, as is usual where sight is defective, plays an important part in enabling the sexes to discover one another. selection here secures success only to such as have the proper odour and the most sensitive organs of smell. in these creatures, as with the butterflies and moths, the odour emanating from the female is most powerful, while the sense of smell is most developed in the male. one of the most striking illustrations of these facts is furnished by that very beautiful species leptodora hyalina—a veritable giant among these small crustacea—wherein the antenn? of the male are produced into enormously elongated comb-like structures, the teeth of the comb being formed by delicate olfactory filaments. in the female these antenn? are extremely short and their olfactory filaments are limited to a small terminal tuft to the antenn?, answering to the larger tuft at the base of the comb of the male.
to the majority of species, however, delicate odours seem to make little or no appeal, since excessive development of the olfactory apparatus, such as is seen in the aberrant water-flea (leptodora), is rare. this is perhaps explained by the fact that leptodora is a species which 262does not herd together in vast numbers, hence, probably, the need of some exceptional means whereby the males may discover the whereabouts of the females, while in the case of the swarming hosts formed by water-fleas and brine-shrimps, for example, no such highly specialized aid is necessary. instead, the males have developed powerful arms for the capture and retention of the females. in the case of the brine-shrimp these arms are of quite formidable proportions. the males of the copepoda, remarks weismann, “possess on their anterior antenn? an arrangement which enables them to throw a long, whip-like structure like a lasso round the head of the female as she rapidly swims away. the antenn? of the male daphnids, too, are in one genus (moina) developed into a grasping apparatus; ... the first antenn? ... are not only much longer and stronger than those of the female, but they are also armed with claws at the end, so that the males can catch their mates as with a fork, and hold them fast. and even that was not enough, for, in addition, the males of most daphnids possess a sickle-shaped but blunt claw on the first pair of legs, which enables them to cling to the smooth shell of the female, and to clamber up on to it to get into the proper position for copulation.
plate 40.
some remarkable devices.
1. a water-flea (moina rectirostris): male showing the claspers-the front pair of “legs,” for grasping the female.
2. the female of the same, in which the “claspers” appear as mere stumps.
3. the aberrant water-flea (leptodora kindlii): the male showing the long comb-like antenna for the discovery of the female (the left only is drawn), and the female, just beneath, lacking this olfactory organ.
4. an extraordinary species of bug in which the upper surface of the thorax has been produced backwards to form an overhanging pent-house, of unknown function, and illustrating the theory of “hypertely.”
[face page 262.
“if we inquire into the manner of the origin of secondary sexual characters of this kind, we shall find that both may have been increased by sexual selection, for a male with a better sickle will succeed more quickly in getting into the proper position for copulation than one with a less perfect mechanism. this assumption does not rest on mere theory, for i was once able ... to observe for a considerable time, under the microscope, a female to whose shell two males were clinging, each trying to push 263the other off. nevertheless, it seems to me very questionable whether the origin of this sickle-claw can be referred to sexual selection, for without this clamping-organ copulation in most daphnids would not be possible. it was thus not as an advantage which one male had over another that the clamping-sickle evolved, but rather as a necessary acquisition of the whole family, which must have developed in all the species at the same time as the other peculiarities, and notably those of the shell. the competition of the males among themselves is thus in this case simply an expression of the struggle for existence on the part of the species as such, and it is not a question merely of a character which makes it easier for the males to gain possession of the females, but of one which had necessarily to arise lest the species should become extinct. in other words, in this case natural selection and sexual selection coincide.
“the case of the antenn? of moina, which have been modified into grasping organs is quite different; these owe their origin, not to natural selection, but to sexual selection, for antenn? of that kind are not indispensable to the existence of the species, as we can see from the closely related genera, daphnia and simocephalus, where the males have quite short, stump-like antenn?, furnished with olfactory filaments not much more numerous than the females possess. just as these supernumerary olfactory filaments were produced by sexual selection and not by the ordinary natural selection, because those males with the more acute sense of smell had an advantage over those in which it was blunted, so the males of the genus moina which could grasp most securely had an advantage over those that gripped less firmly, and thus arose these two different kinds of male characteristics. 264neither of them is of advantage to the species as such, but only to the males in their competition for the possession of the females.”
much uncertainty would seem to exist in regard to two very extraordinary marine species of copepoda. in one, calocalanus pavo the male possesses enormous antenn?, and a remarkable development of iridescent feather-like structures at the end of the body, arranged in a sort of open fan-work; the female has what may be called “normal” antenn?, and a brush-like tuft at the end of the body. in the other species—calocalanus plumulosus—of which the female only is known, there is a similar arrangement of plume-like structures at the end of the body, but all but one are extremely small; the single plume differs from the rest in being of enormous length. commonly these structures are regarded as mechanisms to reduce the expenditure of energy necessary to keep at the surface of the water, for these creatures inhabit the surface-waters of the open ocean. many larval crustacea inhabiting similar areas are in like manner kept afloat, or at any rate aided in keeping afloat, by the excessive development of spines. but if this be the purpose of these strange excrescences of calocalanus it seems curious that the female of c. pavo should not be similarly provided. if they are to be regarded as secondary sexual characters it is curious that the females of c. pavo and c. plumulosus should be so utterly dissimilar. the male of c. plumulosus is unknown. on the whole, it seems more reasonable to regard these strange structures as mechanical aids to swimming rather than as secondary sexual characters.
