Part 2

Romanes finds in the Arthropoda evidences not only of intelligence, but also (in the Crustacea) of reasoning. Bethe, on the other hand, denies that either associative memory or consciousness exists in any of the Arthropoda (Crabs, Spiders, Insects, etc.) The admittedly complex behavior of these forms is ascribed by Bethe entirely to “reflex action,” wholly devoid of psychic elements.

“This opinion,” says Holmes, “is in part based on _a priori_ deductions from the organization of the nervous system and it is held to chiefly by morphologists and physiologists whose observation of the behavior of animals is limited and warped by preconceptions.” Bethe’s experiments were “obviously inadequate.” As Loeb facetiously puts it, “his conclusions are based upon a few spankings he gave a Crab which obdurately rushed into a dark corner (its instinctive action when frightened) despite the presence there of a Devil-fish (Edolene), the Crab’s natural enemy.”

Yerkes and Huggins, Cowles and other observers have found that Crabs and Crayfish are both capable of learning by experience; while Spaulding has demonstrated the capacity of Hermit-crabs (Pagurus longicarpus) to form associations.

HERMIT-CRABS

The Hermit-crab deliberately seeks a partner-Anemone if one has not chanced to attach itself to its adopted shell-home. Grasping an Anemone with its claw, it places it upon the back of the Mollusk (e.g., Periwinkle, Whelk) shell which it had appropriated for its residence, and then adds a second and a third Anemone until it is completely “camouflaged.” If the Crustacean has occasion to remove to a new shell (which it does after each moult), it sometimes carries a partner-Anemone on its great claw, as a form of protection. The Anemone is, indeed, a sort of outer defense, being richly endowed with batteries of stinging cells. Thomson remarks that the Hermit-crab’s behavior is “suffused with an appreciative awareness of what he is doing.”

Recent experiments conducted by Mr. S. Mikhailoff, of the Oceanographic Institute at Monaco, on the Hermit-crab proved conclusively that a complex neuro-psychical activity in animals having neither a cerebrum nor a central nervous system is possible. The animal was able to distinguish differences in shades of red, “refusing to respond to anything except the color which was the ‘educating’ stimulus, even when shades of red very near this were employed.” In Man the power to distinguish between colors and their shades is located in the gray matter of the cerebrum. The Hermit-crab has no cerebrum.

An important conclusion derived by Mr. Mikhailoff from his extensive experiments is that it is a mistake to compare the ganglionic nervous system of invertebrate animals to the sympathetic system of vertebrate animals. He also proved by the experiments in question that it is possible to establish an associated reflex “in response to any external stimulus whatever.”[11]

It is interesting to note in this connection that Crabs, like Birds and other animals, have their own peculiar homing instincts. Carry a shore-crab back from the beach, lay it down, and unerringly it starts back in the right direction, straight for the sea.

“Some land-crabs of the West Indies and North America combine in large swarms to travel to the sea and to deposit therein their spawn; and each such migration implies concert, co-operation and mutual support,” remarks P. A. Kropotkin (“Mutual Aid,” 1902).

FOOTNOTES:

[11] A resume of Mikhailoff’s experiments, translated from the _Revue Général de Science_ (Paris), January 15, 1921, may be found in _The Scientific American_ for April, 1921. Cf. Morgan, C. L., “Animal Behavior,” 1900.

HORSESHOE CRABS (LIMULUS)

In reference to Horseshoe-crabs Kropotkin says: “I was struck (in 1882, at the Brighton Aquarium) with the extent of mutual assistance which these clumsy animals are capable of bestowing upon a comrade in case of need. One of them had fallen upon its back in a corner of the tank, and its heavy saucepan-like carapace prevented it from returning to its natural position, the more so as there was in the corner an iron bar which rendered the task still more difficult. Its comrades came to the rescue, and for one hour’s time I watched how they endeavored to help their fellow-prisoner. They came two at once, pushed their friend from beneath, and after strenuous efforts succeeded in lifting it upright: but the iron bar would prevent them from achieving the work of rescue, and the Crab would again heavily fall upon its back. After many attempts, one of the helpers would go in the depth of the tank and bring two other Crabs, which would begin with fresh forces the same pushing and lifting of their helpless comrade. We stayed in the Aquarium for more than two hours, and, when leaving, we again came to cast a glance upon the tank: the work of rescue still continued! Since I saw that, I cannot refuse credit to the observation quoted by Dr. Erasmus Darwin--namely, that ‘the common Crab during the moulting season stations as sentinel an unmoulted or hard-shelled individual to prevent marine enemies from injuring moulted individuals in their unprotected state’.”

SPIDERS AND INSECTS

Manifestations of intelligence are much more numerous among Insects and Spiders than in the Crustacea and Mollusca. Forel goes so far as to attribute to Insects an “ability to instinctively draw inferences from analogy.”[12]

FOOTNOTES:

[12] Forel, A., “The Senses of Insects,” (Translation) London, 1908.

SPIDERS

Macfarland places the Spiders as following the Cephalopoda in order of intelligence, as does Sir A. E. Shipley. Says the latter:--

“The Arachnida, together with the Crustacea, Insects, Myriapods, and Peripatus, make up the great phylum Arthropoda, a phylum which, from the point of view of numbers of species and individuals, is the dominant one on this planet, and from the point of view of intelligence and power of co-operating in the formation of social communities is surpassed but by the Vertebrata.”[13]

Spiders possess considerable skill as weavers, hunters, miners, builders and aeronauts. Lacking ears, they “feel” sounds. With but limited visual powers, they nevertheless unerringly pick out the particular strand of the web in which a victim Insect has been trapped. It has been said that the Spider must run to the center of the web before she can know which strand to follow out and reach the entrapped victim. Says Gustav Kafka, in his “Animal Psychology,” “Spiders seem to be endowed with a very keen sense of touch, and know instantly along which strand of their web to go in order to get to any Insect or other object that may become caught in their trap.” The layman probably will wonder why the Spider does not take the shortest path to get its quarry, instead of first going to the center of the web, which involves covering a double distance, perhaps on the very next strand of silk. This is probably due to the Spider’s very limited eyesight, in spite of the six to eight eyes which it possesses--so limited, in fact, that it can see ordinarily for a distance of only a few inches.

Nature has provided the spider with an unusually sharp sense of touch, and it can tell, by the vibration of the connecting strand of silk, that some object has lighted on the web. It speeds to the center of the web, from which, by means of its eight legs and this keen sense of touch it can immediately ascertain by the vibration on which radiating strand the object may have alighted. “That is why all Spiders go first to the center of their web to catch a captive that may lie on the outer radius of the web, and that they may even have passed on the way to the center.”

One cannot but admire, says Prof. E. L. Bouvier, “the marvelous vertical orb-web made by those gifted Spiders which are called indifferently Acaneus or Epeira. Radii spaced at equal distances form the framework and connect it with the helix where Insects are captured and which adheres tenaciously to the radii. From the center where the latter converge there starts a guide-line which connects them with the ordinary retreat of the animal. Lurking at its post with one hand, so to speak, upon the guide-line, the Spider perceives the slightest tremor of the web. Has an Insect been caught in the net? If so, it runs down the guide-line until it reaches it, binds it fast, and slowly sucks its sweet juices, on the spot if it is small, but on its retreat if it is strong.”

The sense of touch is developed in Spiders beyond all comparison with other animals. “A female orb-weaver, at the center of her web, can tell friend from foe, male from female of her species, an Insect suitable for food from one not suitable, an Insect of a certain size from an inanimate object of the same size, and she can also distinguish between sizes of any two objects which happen to fly or be thrown into her web. This is all accomplished by touch vibrations passing along the radii of the orb on which the eyes of the female Spider rest. Moreover, during courtship of Spiders this system of touch vibrations is utilized as a means of signals to inform the male concerning the proper mood of the female for mating--but pity the dwarfed male should he misinterpret her signals, for instantly she pounces upon him and devours him without showing the least mercy.”[14]

It has been demonstrated that these little creatures distinguish colors and select a special shade of colors for a background of the marvelously constructed webs. If the observer changes the colors surrounding the web, the Spider inhabitant at once seeks a new location and builds a new web. Spiders must have a sense of light and shade, in order to conceal their webs as they do, and in the case of the so-called “trap-door” variety, to camouflage the cleverly constructed hinged entrances to their tunnel homes so as to resemble their surroundings.

The olfactory pores of both Spiders and Insects are widely scattered over the body, head and appendages. The more highly developed the Insect, the more they are arranged in groups, “most of the groups being found on the legs, wings and mouth parts. So far only a few olfactory pores have been found on the antennæ, these being present on the bases of the antennæ of Bees, Grasshoppers, Roaches and Crickets. Briefly described, an olfactory pore is nothing more than a nerve passing through a tiny hole in the ‘skin’ or chitin of the Insect” (McIndoo, _Loc. cit._, Page 470). “The so-called gustatory sense in Insects is only a phase of the olfactory sense.”

Spiders, according to the latest experiments, are deaf, and only a few are able to make sounds. Most Insects can hear, but the Cicada is said to be deaf, and the female both deaf and dumb. Modern research tends to support Forel’s conclusion that Insects cannot “hear” in the sense that we do. He compares this perception in them to that in deaf-mutes who feel the rolling of a carriage at a distance. But nothing final can at present be said on this question. Schon, for instance, has described a structure in the tibiæ of Bees which he regards as an auditory apparatus. Child thinks that he has discovered an auditory organ in the Mosquito. Many of the experimental results obtained “indicate that Insects can hear” (McIndoo).

The orb-weaving Spiders have no peers in the art of weaving. They know how to fasten marvelously regular webs between the branches of trees, how to pass over rivers on bridges of floating threads, and even when still young, they know how to use similar threads to take flight through the air as real aeronauts.

“The most difficult but not the most delicate work in the making of an orb-web,” says Prof. E. L. Bouvier, “is the establishment of the suspending cable which stretches between two points at a distance from each other and supports the whole structure. Sometimes the Spider fastens its thread at one of these points and then repairs to the other where it stretches and fastens the cord which has issued from its spinnerets during the course of its journey. But this process is not applicable over all sorts of _terrain_ and is even practically impossible when the two points are separated by a stream of water or by any other insurpassable obstacle. In this case the Spider stations itself or suspends itself at one of the points ... and emits a thread which is carried by the wind until it attaches itself at another elevated point. According to Fabre the process may differ somewhat, however: the Spider may suspend herself but soon thereafter reascends by her thread; the latter then forms a loop which is stretched out and fastened by the wind as in the preceding cases. In any case the Spider knows quite well when the attachment has occurred. She then stretches her cable and runs back and forth across it several times in order to multiply the number of threads and thus render the cable more firm. The next thing is to establish another side to the framework: the Spider suspends herself again, then reascends by means of her thread, follows the cable to the opposite end, and then seeks a suitable point further down where she stretches and fastens the thread emitted in the course of the journey.

“In the same manner, or by simply walking from one point to another, a diagonal thread is established which serves as the first radius of the web. Upon this diagonal line a point is chosen to be the center of the structure; the Spider attaches a second radius at this point and then proceeds to walk to the framework where she fastens the other extremity, after which she returns in the opposite direction to stretch this thread and make of it a definite radius; the excess length is reserved at the center to form a cushion. Now at one side and now at the other, in order to render the structure more stable, the Spider attaches new radii by the aid of those already established. When finished the radii are spaced at equal distances; they vary in number according to the species; Fabre counted twenty-one in the angular Epeira and thirty-two in the fasciated Argiope.

“Resting upon the cushion the Spider now revolves repeatedly about her own axis, attaching to the radii a central helix whose inter-radiary elements are straight lines. Then she advances a little farther and begins to establish a second similar helix which extends to the framework. This second helix is permanent in the Nephilæ and temporary in the Argiopæ, the Epeira and most other forms. Since it consists of cylindrical threads it is not very suitable for purposes of capture. Consequently as soon as it has carried it to the framework the animal returns along this helix, placing between its spirals a new helix whose elements are composed of threads bearing sticky globules. This helix constitutes a marvelously effective trap. In establishing it the Spider takes for a support and scaffold the auxiliary helix; but as the work proceeds the latter is destroyed except among the Nephilæ, in which it is retained to give more solidity to the structure.”[15]

Professor Bouvier does not credit the Arachnoidea with much intelligence, and such as they possess he thinks is probably dominated by a strict automatism. Yet he asks, “Is it possible to ascribe to pure automatism or to mere reflex action so judicious a bit of architectural scaffolding? Undoubtedly the psychology of Spiders offers a vast field for observation and experiment.”

It is clear that the Spider is an amazingly good judge of distance, and “can draw parallel lines or converging lines with the accuracy of a draftsman who uses a drawing board and measuring instruments.” It is also certain that they form memory associations and learn by experience: “many examples show that they display a certain degree of discernment when they establish the bases of their shell or nest. And it is by making use of these faculties that they have been able to display plasticity in their habits and undergo an evolution in their industries.

At the present time they are doubtless quite as capable of evolution as in former times, but this tendency escapes our notice because of the automatism which dominates it. We are particularly struck by the extraordinary rôle played by touch in their automatic manifestations. Spiders nearly always perform their labors at night and it is merely by touch that they are able to recognize whether their cables are sufficiently taut, their radii properly spaced, and the spirals of the helix regularly placed. With their legs and their palps they search for contacts and measure distances and the sensitiveness of the spinnerets reveals to them the moment when their silken thread is properly attached. They seem to work as if blind, being largely guided by simple tactile reflexes” (Bouvier).

Says the same authority: “The Avicularidae and the closely related Atypus possess in a very high degree the skill of the miner; they also know how to construct masonry, for before weaving for their retreat an envelope of silk they rough-coat it and make it impermeable by means of a mortar made of earth and saliva.... Fabre has likewise studied the manner in which the Lycosa of Narbonne builds the bastion which surrounds the opening of its burrow. It forms it ‘of little pebbles, bits of wood, scraps of dry leaves, etc., the whole dexterously interlaced and cemented with the silk.’ And again it is the _chelicerae_ which are employed. Many Lycosas, especially among the American species, perform similar labors. McCook reports (1889) that the Lycosa arenicola builds a bastion in the form of a chimney with small bits of straw or wood and that ... at the base of this edifice it builds a little wall of grains or quartz. More skillful still, the Lycosa carolinenses executes a neat bit of basket work; it curves, interlaces and fastens pine needles, so as to form a sort of bastion in the shape of a bird’s nest upside down.”

In discussing the mystery of the Spider’s web-weaving dexterity, Prof. J. Arthur Thomson, in his chapter on “Animal Intelligence,” (“The Outline of Science,” vol. 2) says:

“To credit animals with reason, which means experimenting with general ideas, is, in all probability, too generous. To try to reduce them to the level of automatic machines is certainly too stingy. The fact is that the behavior of animals is often intelligent, often instinctive, and often a subtle mingling of the two. But it is necessary to attach precise meanings to these terms.

“A young Spider, which never made a web before, may make its masterpiece true to the specific pattern the very first time. It does it without any model to copy, and with no trace of the prentice hand. Sometimes it can make the web in the dark, or in the course of a forenoon. This is instinctive behavior, depending on hereditary prearrangements of nerve-cells and muscle-cells, though never without its psychical aspect--a suffused awareness and a background of endeavor. But apart from theory, the fact of observation is certain that inexperienced animals suddenly blossom out into extraordinary intricacies and niceties of behavior, perfect the very first time, not requiring to be learned. This is instinct.”

“With reference to the intelligence of Spiders,” remarks Mr. Garrett P. Serviss, “I find among Mr. Belt’s records an account of the terrible panics caused by the advance of armies of Ants through the forest, all sorts of Insects fleeing wildly before them. But a Spider sometimes escaped by running out to the end of a branch and suspending itself from a single thread of silk, between the enemies above and the enemies below.

“There is exhibited an extraordinary repugnance by many people against admitting that any living being on this earth has been furnished with anything in the slightest degree resembling the peculiar gifts that assure to our race its immensely superior status. This seems to me a petty jealousy. When we dissect the motives of the human heart do we discover any reason why Man should be the exclusive possessor of sparks of Divine light?”

FOOTNOTES:

[13] Cambridge Natural History, IV (1909).

[14] McIndoo, Dr. N. E., “The Senses of Insects,” Annual Report Smithsonian Institution for 1920, Washington, 1922.

[15] _Scientific American_, February, 1920.

BEETLES

Although the Burying Beetles (Necrophorus) live an isolated life, generally speaking, they know how to call for help when it is needed, and their appeals for assistance never go unheeded. As is well known, they must have some decaying organic matter to lay their eggs in, thus providing their larvæ with food. But the food must not decay too rapidly, and in order to slow up the process of decay the Beetles bury the corpses of all kinds of small animals.

Occasionally they find the corpse of a Bird or Mouse, which is too heavy for them to “handle” unaided. They thereupon call on their fellow Beetles for assistance, and from four to ten Beetles respond. Uniting their efforts they transport, if necessary, the corpse to a suitable soft ground, where together they bury it. When Gladitsch attached a dead Bird to a cross made out of two sticks, or suspended a Toad to a stick planted in the soil, “the little Beetles would in the same friendly way combine their intelligence to overcome the artifice of Man.” The same evidence of intelligent mutual aid has been noticed among the Dung-beetles.

WASPS

Not many years ago it was confidently asserted that “Man is the only tool-using animal.” Now we know that not only do members of the Ape family employ sticks for weapons and even for crowbars, and also use various objects for missiles, but even in the Insect world we find a creature, the Solitary Wasp (Ammophila), which makes a door of soft earth for its nest and then picks up a small pebble in its mandibles and hammers the edges of the door more securely, just as a man would use a pounding-iron. This phenomenon, observed by the Peckhams in 1898,[16] has been verified by other investigators.

“Before we could recover from our astonishment at this performance,” wrote these now famous observers, “she had dropped her stone and was bringing more earth, and in a moment we saw her pick up the pebble and again pound the earth into place with it. Once more the whole process was repeated, and then the little creature flew away.”

Professor Thomson came to the conclusion that the Wasp’s use of the pebble for a mallet “is not part of the instinctive routine but is an individual touch, probably with more vivid awareness than is associated with the rest of the agency. The difficulty is to think of the origin of either the routine or the finishing touch without postulating intelligence or at least some appreciation of significance.”

Bouvier points out that the use of the little stone is not yet a fixed habit with Ammophila urania, belonging “only to certain individuals more highly endowed than others, and is perhaps only accidental even with them. Maybe it will finally pass into the instinctive habits of the species; for the present it belongs to the domain of individual intelligent acts.”

It should here be noted that in the psychological history of the Articulata we witness the gradual transformation of intelligent acts into instinctive acts, whereas the path of evolution in the Vertebrates seems to lead from instinct toward intelligence. It is reasonable to infer, however, that the instincts of the Vertebrates were preceded by an intelligent process and the establishment of new habits, “which by heredity became part of the patrimony of instinct, modifying the latter and constituting elements essential to its evolution.” (Bouvier, E. L., “La vie psychique des Insectes.”) “It is intelligence,” continues this same high authority, that “regulates by appropriate selection all manifestations of race memory; intelligence again, in the sundry forms of association and individual memory, that puts together the most complicated mechanisms of instincts.”