Mimicry.

From: American Spiders and their Spinningwork
Henry C. McCook


I.

An interesting example of the power of spiders to adapt themselves and their industry to circumstances occurred under my observation in the case of a Turret spider, Lycosa arenicola. Wishing to preserve a nest to study the life history of its occupant, I carefully took up the sod containing the tube, carrying away with me several inches in depth of the burrow. The upper and lower openings were plugged with cotton to retain the spider during transit. Upon arrival of the nest in Philadelphia the cotton plug guarding the entrance was removed, but the other was forgotten, and thus allowed to remain. The nest with the enclosing sod was imbedded in the soil inside of a tub, and the spider left to work out naturally its industrial instincts. It immediately began removing the cotton at the bottom of its burrow, and cast some of it out upon the surface. But finally, guided, apparently by its sense of touch, to the knowledge that the softer fibres of the cotton would be an excellent material with which to line its tube, she put it to that use, and had soon spread a smooth layer over the inner surface and upon the opening. In this manner the interior was padded for about four inches from the summit of the tower downward. It may be taken for granted that this Turret spider for the first time had come in contact with such material as cotton, and had immediately utilized its new experience by substituting the soft fibre for the ordinary silken lining, or rather by adding it thereto. This nest, with the cotton wadding, is represented at Fig. 38. The cotton was distributed quite evenly over the walls of the burrow and tower, and had evidently been beaten down and pushed in after the manner of Lycosids and Agalenads when beating in the spinningwork of their cocoons and the silk lining of their burrows and tubes.

Arachnids

Tarantulas
Other spiders
Scorpions
Other arachnids

Mrs. Treat having learned how this spider, which had been taken from her grounds, had used the cotton, was led to make several experiments. She placed cotton by the side of seventeen burrows, both of the Turret and Tiger spiders, situated upon her lawn, and found eight of the number used the cotton as a lining, but none as artistically as the one above described. She then went to the edge of a wood, some distance away, and placed cotton by the side of eleven burrows there located. None of the occupants availed themselves of the artificial lining. This seems a curious fact, but the theory which the author uses to account for it, namely, that the individuals upon the lawn must have been descendants of species colonized from New England in the neighborhood of a cotton manufactory, can hardly be accepted. My recollection is that all these creatures were natives of New Jersey. I am sure at least that the one which wove the cotton lining for me was a native New Jerseyman.

One specimen of those situated upon the lawn not only used the cotton fibre for the lining, but also for a cover or door of its dwelling. This door she made smooth on the side, and fastened it firmly down on the outer edge of her wall. (Fig. 39.) She did not make the same use of the cotton that she would of soft moss, which she sometimes uses in building. The fibre of the cotton was drawn out and interwoven among the sticks around the upper portion of the tower, and made to take the place of ordinary web work.1 I have this nest in my collection and give a drawing thereof, Fig. 39. The use of the cotton is curious and interesting, and remotely suggestive of a door, perhaps. But such use is not clearly shown. These examples suggest no little elasticity of intellect on the part of these spiders, for they were at once able to perceive the usefulness of the new material brought within the range of their experience, and easily adapted it to their special needs in lining the interior of their towers. Were they conscious that such soft, pliable material permitted economy of silk secretion, and could that have been a motive for its use? These facts start a most interesting train of reflection and conjecture, and suggest a fruitful field of inquiry and experiment to one who may have both disposition and opportunity to engage therein.

II.

I took a female Epeira trifolium from her nest in order to observe the changes of color. She was kept within a glass vessel for forty-eight hours, and then returned to her old web and placed upon it near the centre. The web was about as when she left it. She paused about a half minute, seized the trapline, taking precisely the position and in the exact spot which she had occupied for several days before. Did she remember her nest after the forty-eight hours’ interval? The same fact as to memory of local snare and nest was tested upon another Trifolium, with the same results. The example above quoted indicates that Epeira trifolium preserved during twenty-four to forty-eight hours a recollection, or at least a perception of some sort, of its old quarters within its home nest.

Yet stronger examples may be cited of spiders remembering their homes. The Trapdoor spider, for example, that constructs its ingenious hinged door upon a bed of moss or lichen, and then covers the lid with plants precisely like those surrounding it, when it leaves its den and goes out upon excursions for food, and returns without difficulty to its home, certainly has preserved distinct recollection of the location of that home.

Again, the Tiger spider makes a burrow underneath beds of moss, erecting over it a vestibule or dome composed of the material everywhere surrounding the spot. From this she sallies forth into the vicinage, often making wide excursions after prey, and returns either by day or night to her nest, notwithstanding its general likeness to the environment. This is true of Lycosids generally. The mother Lycosa in the cocooning period oftens erects a cell or cave, underneath a stone or in like positions, which is partly lined with silk, and sometimes has a pretty approach to the surface between the sprays of grass, clover, or other vegetation, as may be seen in Vol. II., Fig. 175, with the nest of Lycosa scutulata.2 From this retreat Lycosa will sally forth after food, dragging her egg sac behind her. It may seem a little strange that she should do so, and one might be inclined to think her rather stupid not to leave this treasure at home. Nevertheless, she attaches it to her spinnerets, and carries it with her in all her excursions, and thereby, no doubt, saves it from parasitic and other enemies. Having secured her food she returns to her cell, and notwithstanding the manner in which it is secreted, finds it without difficulty.

So also Saltigrade spiders, and others of like habit, who issue from their silken cells to stalk their prey on walls and trees, appear to find their way to their homes without difficulty. These facts indicate on the part of these spiders a good memory of the location of their domiciles, and a sense of direction sufficiently developed to bring them upon the return path with accuracy.

Of course there is nothing remarkable about this, for such facts are true of the insect world generally. It is known by all bee hunters, and by all keepers of bees, that either the wild or the hive bee will find its way home after a long excursion in search of honey. So also I have frequently observed the mud dauber wasp erecting its clay cell upon a wall or, building, making excursions to all points to secure mud for her masonry, and invariably return with her mandible hod full to complete her nidus. The same accuracy of memory, again, is shown when, having finished her nest, she prowls through all the neighborhood in search of spiders, winging her course to all points of the compass, prying into nooks and crannies and out of the way places, mousing under leaves and diving into flowers, and yet always directing her return course without the slightest hesitation to her mud daub cell. It is needless to multiply such examples, and I only allude to them to show that in this respect the spider is not peculiar, but is gifted, like other Arthropods, with a memory sufficient for all the purposes of its life.

III.

Mr. F. M. Webster recently wrote me from the Ohio Agricultural Experiment Station (February 17th, 1892) a note which contributes an interesting item to the subject of mimicry as discussed Vol. II., Chapter XII., especially under Color Mimicry and Mimicry of Environment. A spider observed by him had mimicked the white excreta of birds so perfectly as to deceive this thoroughly trained and accurate observer. The color of the spider was whitish, with the dorsal abdominal portion clouded with blackish, exactly resembling a mass of bird droppings. The deception was further carried out by the spider having spun a thin irregular sheet of white web on an elm leaf, in the midst of which it was situated with legs drawn up. At the distance of a few feet the observer was completely deceived; he thought it the excrement of a bird until he had the leaf in his hand. The appearance of the semisolid mass within the white splash of semifluid matter was so closely counterfeited, that Mr. Webster says he was truly provoked that such an animal could so befool his eyes after all his years of training. Judging from the general description sent, I infer the species to be our old friend Misumena vatia, so famous both in America and elsewhere for its color mimicry.

Mr. Webster’s observation is all the more interesting because of its exact correspondence with one of which he was not informed until I called his attention to it, which has received considerable attention from naturalists. Mr. Henry O. Forbes relates a similar experience of deception.3 He had been allured into a vain chase after a large stately flitting butterfly (Hestia) through a thicket of Pandanus horridus, when on a bush that obstructed further pursuit he observed one of the Hesperidæ resting on a leaf upon a splash of bird dropping. He had often observed small Blues at rest on similar spots on the ground, and had wondered what the members of such a refined and beautifully painted family (Lycenidæ) could find to enjoy in food so seemingly incongruous for a butterfly. He approached with gentle steps and ready net to see, if possible, how the present individual was engaged. It permitted him to get quite close, and even to seize it between his fingers. To his surprise, however, part of the body remained behind; and in adhering, as he thought, to the excreta it recalled an observation of Mr. Wallace’s on certain Coleoptera falling a prey to their inexperience by boring in the bark of trees, in whose exuding gum they became unwittingly entombed. He looked closely at the excreta to find if it were glutinous, and finally touched it with the tip of his finger. To his delighted astonishment he found that his eyes had been most perfectly deceived, and that the excreta was a most artfully colored spider lying on its back, with its feet crossed over and closely adpressed to the body.

The appearance of recent bird droppings on a leaf is well known. Its central and denser portion is a pure white chalk like color, streaked here and there with black, and surrounded by a thin border of the dried up more fluid part, which, as the leaf is rarely horizontal, often runs a little way towards the margin. The spider observed by Mr. Forbes, like that seen by Mr. Webster, was pure chalk white in general color, with the lower portions of its first and second pairs of legs and a spot on the head and abdomen jet black.4 It had woven on the surface of the leaf, after the fashion of its family, an irregularly shaped web of fine texture, which was drawn up towards the sloping margin of the leaf into a narrow streak, with a slightly thickened termination. This form, as described by Mr. Forbes, was doubtless determined by the concavity of the leaf, and the facility which the slightly turned up edges gave for making good points of adhesion, at the same time leaving a little space between the netted spinningwork and the leaf’s surface over which it was stretched. According to Mr. Forbes, the spider takes its place on its back upon this irregular spinningwork, holding itself in position by means of the spinal armature of the legs thrust underneath the web, and crosses its legs over its thorax. I do not remember to have observed any Thomisoids in this position, but have always seen them crouching with back upward when not using a web. I would suppose that if they used a snare at all they would rest underneath the same with their backs downward toward the leaf, after the fashion of many other spiders. However, Mr. Forbes is so precise in his statement that one feels it necessary to accept it. As thus arranged, he speaks of the whole combination of spider and web as being “so artfully contrived” as to deceive a pair of human eyes intently examining it.

This similarity of habit in spiders of the same family, at such widely separated points as Java and the United States, is in itself interesting. It is also interesting to notice that two thoroughly trained observers should have independently named the same rather outre object as the one suggested by the spider’s mimicry. Nevertheless, one is inclined to think that the suggestion of mimicry is a bit of anthropomorphism. Because suggested to the mind of the observer, it does not follow that any such deception had been devised by the spider. All the individuals of this family and tribe are in the habit of seeking their prey chiefly upon trees and plants of various sorts, stones, et cetera. They may often be found upon the white or whitish gray spots, or upon dried bits of lichen or moss found on plants. In such positions they certainly strongly suggest the idea of intentional mimicry. However, in point of fact, the combination might have been accidental so far as the spider is concerned. In the cases observed by Messrs. Forbes and Webster there appears no reason to infer that so subtle a process as that attributed to the spider could have found lodgment in its mind.

At least, if we accept Mr. Forbes’ theory of an artful contrivance, we must conclude that this lowly organized animal could intelligently survey the field, put this and that together, select certain spots for settlement after determining its own color resemblance to such spots; then deliberately proceed to spin a web which, in its general contour, would resemble the particular form which semifluid masses are wont to assume in various positions, according to the inclination of the plane upon which they fall; and then, further, arrange its own body in such relation to the web as to present the appearance of mottled black and gray characteristic of bird droppings under like circumstances. The ability for such mental processes would undoubtedly establish an order of intellect and powers of observation and reasoning beyond those which we are at present warranted in attributing to a spider. All the facts can be accounted for, and are most naturally accounted for, without introducing a factor so strongly imaginary. I am disposed to think that the web as described was spun in an ordinary position, in the form habitual to the species, and in such locality as it usually frequents; moreover, that this was done without any intention to perpetrate a mimicry such as the observer fancied, and which in fact existed simply as an analogy in his mind.

But excluding the idea of intentional deceit, the mimicry of Ornithoscatoides has been explained as a product of evolution through natural selection and survival of the fittest. The explanation implies that the existence of those individuals practicing the mimicry at first and accidentally had been preserved by the greater abundance of food or other advantage gained thereby, until it became a permanent habit. But we have only an inference that the habit is permanent in Ornithoscatoides. The facts recorded by Mr. Forbes stand entirely alone, and it seems more likely than otherwise that an extended observation of that spider would show that the same condition obtains as to its habits that we have observed in Misumena, and that it will be found to spin a web substantially as described by Mr. Forbes, in many positions which would preclude the supposition of usefulness through resemblance to the excreta of birds; as, for example, on the under side of leaves, underneath limbs of trees, between and under stones, hedges, etc.

As to Misumena, we know that the case reported by Mr. Webster is absolutely unique as yet; knowing somewhat the general economy of this species we can confidently affirm that the incident is exceptional. Misumena spreads her cocoon nest in various positions, and is by no means limited to such locations as described by Professor Webster. One of these positions has been described and figured in Vol. II., Fig. 188. The general form of the cocoon nest is as there exhibited, and in choosing the site thereof the mother appears to give herself as wide range as do other species of the order. In other words, she puts her cocoon and the nesting tube surrounding it in such place as is most convenient to herself when the maternal function urges her to action.

The spinningwork described by Mr. Forbes I take to be the cocoon nest of Ornithoscatoides, for it is not the habit of the Laterigrades generally to get their food by means of snares. They belong to the Wandering group of spiders, and stalk their prey along shrubbery, branches of trees, rocks, walls, etc. If this inference be correct, the peculiar web observed by Mr. Forbes is limited to the cocooning period, at which time Laterigrade spiders are usually found within or lurking around the little tent which overspins their egg sac. It must follow that the effect of industrial mimicry upon the preservation of that species must have been confined to a brief period at the end of the spider’s life. To account for such mimicry as a product of the survival of the fittest through natural selection, one needs to conceive of the selection as operative in the early and most impressible stages, or at least during the active period of life, and not during the few days immediately preceding death.

IV.

In the second volume of this work (Vol. II., Chapter XI.) I ventured to express a suspicion, which I have sometimes entertained, that the color surroundings of the spider, in some manner not now explicable, may so rapidly influence the organism of the creature that a change of color is produced in harmony with its environment. I there raised this query: Can a spider have the power to influence at will the chromatophores or pigment bodies, so that she may change her color with the changing sites?

Mr. H. H. J. Bell has recently communicated an observation5 which appears to be confirmatory of this suggestion. While traveling along the West Coast of Africa between two small towns on the Gold Coast (August, 1892), he was attracted by the appearance of what he supposed to be flowers upon the bushes bordering the path. On examining these he found that they were the webs of an orbweaving spider, whose spinningwork, according to the published description, resembles that of Argiope, as heretofore fully described by me. The spider’s body was a light blue color; and the legs, which were symmetrically disposed in the shape of an X across a white ribboned hub, were yellow, ringed with brown. The body of the spider resembled the corol of a flower, and the crossed legs gave it the semblance of petals. Mr. Bell speaks of the illusion as remarkable, and supposes this mimicry of an orchidlike flower serves not merely to protect the spider, but rather as an attraction to butterflies and other flower frequenting insects on which the aranead preys.

The most interesting part of the observation, however, is the strange facility which the spider possessed of changing its color. Mr. Bell captured her in a white gauze collecting net, which was placed beneath her and into which she dropped when disturbed, as is the custom of many species. As soon as she touched the net the blue body color became white. On being shaken her body turned to a dark greenish brown. She was then placed in a glass tube, and gradually resumed her blue tint, but when shaken up always turned to a greenish brown. When placed in spirits the spider’s color became a gray brown, and so remained. The observation was repeated with like result, except that the second individual did not turn white, but passed immediately from her normal blue into a dark greenish brown. I have no comments to make upon this interesting and, as it seems to me, important observation, but give it place here, as of undoubted value in its bearing upon the interesting and perplexing problem of mimicry as it is presented in the life history of the various aranead species. I have never observed and do not remember ever to have read of such instant and volitional changes of color. The slight changes which I have noted in spiders having metallic colors have been due to the play of light falling at and seen from different angles. The numerous and striking changes in the Shamrock spider (Epeira trifolium), so well illustrated in Plate I. of Vol. II., are produced gradually, and cannot be compared with the chameleonlike changes of the blue Orb-weaver observed by Mr. Bell.

V.

The trapdoor building habit is remarkable in its distribution over nearly every part of the globe in tropical and semitropical regions. From whatever part reported, Europe, Africa, Asia, Australia, or North and South America, the nest shows the same peculiarities of structure, and the architect appears to live in the same way. Even the habit of mimicking the surrounding surface by attaching sundry small plants is cosmopolitan. Moggridge in his charming book has already made us familiar with this form of mimicry in the European species; it seems also to characterize our southwestern trapdoors, and appears in Cambridge’s Idiops Colletti, a Burmese (India) spider.6 In the interesting description of General Collett, which Mr. Cambridge publishes, it is stated that the upper surface of the door is often covered with a dry black lichen growth. There are generally a few withered grass blades worked into the edge of the door, or into the edge of the mouth of the burrow, so as to form a kind of semicircular fringe, which often catches a practiced eye and leads to the detection of the hole. The grass blades are probably inserted to aid in assimilating the outside of the door to its surroundings, a purpose in which, General Collett opined, they certainly fail so far as the human animal is concerned. In a few cases he noticed also grass blades wrought into the general surface of the door, which in the dry season, when the grass is everywhere withered, certainly aid in its concealment. But during the season when the adjacent grass is green one would think that yellow withered grass blades on or near the burrow mouth would tend to make it conspicuous. I have considered at some length, Vol. II., Chapter XII., the point thus raised independently by this intelligent observer, and its relation to so called mimicry of environment. I need only add here that one can hardly be asked to consider protection against human intelligence as a factor in the action of a spider’s mind. The hostile elements which influence it are of quite another sort from the curiosity of a naturalist and the plundering of a collector.