Popular Science Monthly/Volume 61/August 1902/Some Observations on the Behavior of the Social Wasps




LITTLE has been published concerning the social wasps since de Saussure wrote so interestingly of them nearly half a century ago. His work is justly regarded as a classic, but unfortunately it has become so rare that, nowadays, it is inaccessible to the average student, and accurate knowledge of the group, save that derived from an occasional disagreeable encounter with one of its members, is meager indeed. Moreover, the wonderful ingenuity displayed here, and among the highest Hymenoptera, the care for the young, and provisioning against the rainy day have served, not only to point a moral, but to credit these forms with an intelligence second only to the human. Even those who adopt a purely mechanical explanation of animal activities are inclined to except the bees and wasps. Mr. E. L. Thorndike, in his general conclusions concerning the nature of animal intelligence, makes reservations in favor of this group, while Mr. and Mrs. G-. W. Peckham, in their admirable study of the solitary wasps, contrast them with the social wasps in the following terms:

The social Hymenoptera are born into a community and their mental processes may be modified and assisted by education and imitation, but the solitary wasp (with rare exceptions), comes into the world absolutely alone.... It must then depend entirely upon its inherited instincts to determine the form of its activities and, although these instincts are much more flexible than has generally been supposed and are often modified by individual judgment and experience, they are still so complex and remarkable as to offer a wide field for study and speculation.

The conclusions noted here, derived from the study of a group which is among the more primitive social Hymenoptera, may then be of interest as contributing somewhat to problems which are receiving anew the attention of both the naturalist and the comparative psychologist.

General Account.

In the tropics of the Old and New World, the family of social wasps or Vespidæ comprises seven genera, but only three of these, Polistes, Polybia and Vespa are represented in the United States. Of these, Polybia is the smallest and rarest, being restricted to California and Florida; Vespa is widely known as our common hornet or yellow-jacket, while Polistes is smaller and more timid and its colonies never reach such formidable dimensions as those of Vespa.

Here, as in the other genera, the colony consists of three kinds of individuals—males, females and workers or neuters, and is founded usually[1] by a single female somewhat improperly called the queen. She, with perhaps several other females, is the sole survivor of a colony of the previous season, and has passed the winter in some warm crevice or sheltered corner. During the first warm days of spring, she may be seen seeking a suitable nesting-place and, this found, she begins the construction of the nest, which has the appearance represented in the accompanying figure. Each cell contains an egg suspended near its apex by the aboral end, and in the course of a few days this egg develops into a worm-like feeding larva. The queen works incessantly when the weather permits, increasing the number of cells, lengthening the cells already there and strengthening the stalk which supports the whole, so that when, at the end of six weeks—the first workers emerge, the nest may comprise as many as forty or fifty cells. From this time the workers gradually assume all the duties of the colony except the egg laying,[2] though, as far as I have observed, in a spirit[3] far different from that of the queen. Thus, one nest, which at the beginning of July was made up of forty-three cells, and represented the work of a single queen or mother, contained at the end of the season only one hundred and twenty-seven cells, the eighty-four additional cells being presumably the product of at least fifty workers which had emerged during the summer months. Toward the latter part of August and early September the males and females appear, and the nests are more and more deserted for the flowers and fruits of autumn. Here the males and females mate, the workers and males linger through the warmer days, while the fertilized females alone survive the winter and lay the foundation of the new colony in the spring.

The Site of the Nest.

This varies for different localities and to a certain extent in different species. In Wisconsin, where most of these studies were made, the preference seems to be for the sloping under side of old roofs, eaves and the protected casements of windows. Indeed, so strong has been the attachment to certain sites, that I have several times seen the wasps suspending one comb from another in the style of architecture characteristic of the hornet. In New England P. pallipes builds in the. open on wild rose bushes and other low shrubs, in protected recesses of stone walls, while a tin can, a water pipe perforated by rust and a sheep's skull are other nesting places which have come to my notice. At Willow Grove, Pa., great numbers have made use of the space enclosed by the sheet-iron water-table of a new car barn, thus securing a maximum of warmth and immunity from the zealous wasp hunter. In Texas, I am told, certain species build on the cacti, while others prefer stone ledges; and doubtless further observation will disclose many other interesting variations in the nesting habits.

The Nest and its Construction.

The nest, as is well known, consists of a single layer of hexagonal paper cells. It is modeled from a soft gray pulp which is a mixture of fibers of weather-worn wood and a secretion from the wasp's mouth. The little ball of semi-fluid pulp is applied roughly by means of the fore legs, all along the edge of the cell to be extended, making an irregular addition about four times as thick as the cell wall. The wasp then walks back and forth for two or three minutes continually touching the material with her antennae, and with her mandibles pats and smooths it into shape. This operation extends the wall each time from one eighth to one fourth of an inch, depending of course on the size of the ball of material at the beginning. In addition to this, the wasp applies a glutinous secretion which renders the paper tough and waterproof, the nests built in the open being more thickly coated than those sheltered from the rain and dew.

The geometrical sense of the bees and wasps has long been a matter of controversy. In Polistes, so far as I have observed, the first cells always approach a circle in cross-section, and the six-sided form is the result of the flexibility and the consequent compressing of the walls. Once pressed into shape, the material added may take the same form, and the artificer appears to possess a superior mathematical sense; but that the cells are not intentionally fashioned thus may be seen by examining those first formed, or those comprising the margin of the nest at any later stage of construction. These are always circular in outline.

The Care of the Young.

The larvae, which develop in a few days from the eggs, are fed from this time until the beginning of the pupal stage both with nectar and proteid matter. The nectar is obtained from flowers, is stored for a time in the crop of the mother or the nurse, and then regurgitated into the mouth of the larvae. This process may be easily watched in the case of captive wasps. They nearly always make the round of the cells containing feeding larvæ some minutes after partaking of the sugar solution provided as their store of food. The animal food consists of caterpillars which have been worked by the mandibles into a mass about the consistency of marmalade.

This wasp does not sting her prey. Her habit is to seize the squirming caterpillar in her fore legs, pass it back and forth several times between her mandibles until it is quite limp and dead, and then to roll it deftly into a ball and hold it between the fore legs while she flies to the nest. There, the operation is continued three or four minutes longer, until the malaxation is complete. In distributing the food, the mass is held firmly against the ventral side of the thorax, by means of the femora of the first pair of legs and a bit partly pinched off with the mandibles. Next, the wasp inserts her head into a cell, lightly touches the larva with her antennas, causing it to stir and open its mouth, and then pushes the bit of food into the mouth with the tarsal joints of the fore legs. With the remainder, the wasp now passes to another cell and the process is repeated until the ball of food is used up. Observations on the social Hymenoptera indicate that the polymorphism occurring here is in large measure dependent on the kind of food given to the larvae. So far I have no evidence that Polistes exercises any selection in the quality or amount of food furnished the larvae which are to develop into the various members of the wasp community.

The foregoing constitute the chief activities of Polistes, but several other minor performances may be briefly noted. Among these are the stroking and rubbing movements which serve to keep the body clean. They are chiefly six in number: (1) Hanging by the four posterior legs, while doubling the first pair backward over the head and repeatedly passing them forward over the face and antennæ. The latter are thus drawn between the tibiæ and the spurs which these bear on their distal ends. (2) Drawing the first pair of legs alternately between the mandibles, and thereby removing any foreign substances accumulated by them during the first step of the process. (3) Doubling the first pair of legs as above mentioned and passing them backward over the dorsal surface of the thorax and the bases of the wings. (4) Hanging by the two anterior pairs of legs and passing the hindmost pair backward over the abdomen and the folded wings. (5) Suspending the body by the first pair of legs and drawing each of the others in turn between the tibial spurs of one of the remaining legs. (6) Drawing the wings alternately on each side between the abdomen and the hindmost leg of that side. These are sometimes gone through in the order given, but not necessarily so; some of the steps may be altogether omitted, although the movements of the anterior usually precede those of the posterior appendages.

Then the wasp makes frequent careful inspection of the cells of her nest. She may return every few minutes in the interval of her other activities apparently for the sole purpose of satisfying herself that all is well. To test the wasp's power of observation I have several times cut away a bit of the cell wall. In one case, the mutilation was immediately detected and an attempt made to repair the breach. Once, one of the eggs was replaced by one from another nest. When, in the course of the customary examination, this cell was reached, the wasp paused, gazed long and fixedly, as if unable to believe the evidence of her senses, and then with signs of great agitation, cleaned the cell out and deposited a new egg of her own. To ascertain whether the mucilage by which the egg was attached was the exciting cause, several eggs were smeared with it and left in their original positions. In this case the mucilage was carefully removed, but the eggs were left untouched.

Polistes is said also to store honey in the cells from which the perfect imagines have emerged. In the height of the season these cells are used a second time for the development of the young. They are then carefully renovated before the egg is deposited. I have never yet found honey stored in the nests taken, but in two nests which were kept indoors for the purpose of experimentation, many of the cells were found to contain a few grains of perfectly transparent sweetish substance which undoubtedly had been elaborated from the sugar solution forming the food store of the little colony.

The Larval and Pupal Periods.

The sole activity of the young during the three weeks' larval period appears to be the feeding on the elaborated nectar and proteid matter furnished by the mothers or the workers. At the end of this time the larva spins a silken lining and a covering for its cell. This is done by passing the head from point to point of the cell wall while a glairy fluid issues from its mouth and hardens into a delicate silken thread. I have noticed a considerable difference in the form of the cell covering. Under normal conditions, the cell is lengthened by the workers or queen to suit the increasing size of the larva, but in captivity the wasps cease the work of construction though they may still continue to feed the larva?. The cell is therefore too short for the full-grown larva. In such cases it not only lines the cell but extends the wall with the same silken substance, finally capping it with a dome-shaped cover. This apparent forethought on the part of the larva is entirely accounted for, when we see that in spinning its cocoon the larva begins near the bottom of the cell, gradually approaches its mouth and finally stretches as far as possible beyond it. If the cell wall is already sufficiently extended, this serves solely as a lining, if not, as, in part, extension to the original cell, providing the space necessary for the metamorphosis.

During the three weeks of the pupal period the pupa is quiescent, except for occasional twitchings of the abdomen. About two days before emergence the muscles of the appendages begin to undergo periodic contractions, which carry the pupa to the end of the cell, and rotate it to some degree. At the same time the jaws become functional, and the continued action results in the removal of the lid of the cell and the emergence of the wasp to assume its share in the duties of the wasp community.

Behavior of the Newly Excluded Worker.

The study of the newly excluded wasp is extremely interesting and throws some light, I think, on the character of its mental activities. There is at the outset considerable variation observable in its actions. Sometimes the little worker does not take the trouble to cut the lid of its cell entirely away, occasionally it not only cuts away the lid, but neatly trims the edges of the cell, and very rarely it pushes its head into the cell, as if to satisfy a curiosity concerning the place whence it has come, even making comparisons from the contents of neighboring cells. But I question whether this performance is rewarded by any intelligence.

Emergence accomplished, there ensues a period of quiescence, which for the most part is passed on the back of the nest, and which is probably necessary to the proper hardening of the tissues. Meanwhile the queen does not cease her labors, but makes it her first duty to clean out the cell left vacant by the newly excluded imago and lay an egg in it. Returning, perhaps, a little later with a ball of food, she thrusts it into the face of the worker, but no notice is taken of it, and she proceeds alone with the work of malaxation and distribution. This may be repeated several times before the young worker finally accepts the urgent invitation to take up its family responsibilities. There is no doubt that the worker sees what the queen is doing, and when, after apparently watching her go through the process of malaxate and dispensing the food several times, it comes up to take part of it and do the same, the inference is perfectly natural that the worker is imitating its mother. This idea is strengthened when we observe that it takes the young one about three times as long as its mother, to accomplish the task of feeding, and that there is great uncertainty displayed in offering the food to the larvae. The young worker is apt to waste much time in poking its head into the wrong cells, and running unnecessarily about over the face of the nest.

To test whether the worker learns to do its work by imitation, I removed one nest, whose founder was missing, to a place half a mile distant from any known nest before any of the workers had emerged. After the appearance of four workers, fresh caterpillars were repeatedly offered them. Two weeks passed before this met with any response, whereupon one day they all surprised me by coining up and very eagerly preparing and distributing the food. I have since made sure that the nursing habit is entirely independent of the example of the mother and, further, that its appearance is to some extent variable for different individuals.

In the experiments conducted the past summer, bits of the larvæ of the Ribbed Rhagium, a beetle whose eggs develop under the bark of decaying trees, were offered at intervals to the newly excluded neuters before they had had any association with others of their kind. With slight exception, great trepidation, or rather movements which I interpret as indicating fear, was shown at the first appearance of the morsel. The wasp retreated precipitately from the proffered morsel, sometimes turning and running away in the wildest manner imaginable. But usually when the bit had been presented for the fourth or fifth time (at intervals of one half to one minute), the wasp would no longer back or run away, but stop and look at it. The next action was to touch it with the antennæ and finally it was seized and disposed of in the customary manner. Usually the experiment met with success in the way described if performed any time after the first half day of imaginal life. But I have seen a worker not four hours old spontaneously go through the same reaction while others waited several days before manifesting the instinct.

The whole process seems to be a reflex called forth by the presence of the food, and an important factor in calling it forth is hunger on the part of the wasp. It is highly probable that in the crushing process liquids are extracted from the mass, which are swallowed by the wasp. I have frequently seen them chew at morsels without molding or mixing them, and even dropping the mass to lap up the liquid which had exuded from it. Once started, however, the reflex unfolds in the natural order, first the crushing and molding, then a slow marching round the nest with frequent pauses, and, if larva? are present, the pinching off of the food bit by bit until all has been disposed of. If no larvæ are present, if, for instance, the young worker is living in an inverted tumbler and has never seen a larva the various stages in the process are the same. It will run searchingly over the glass and pause every few seconds to thrust the ball against it. This naturally meets with no success and the food is again worked over and the process repeated, perhaps several times, before the bit is dropped and not again noticed. Very rarely the wasp will attempt to fly with its burden, although naturally, since it has had no association with a nest or larvæ, it flies nowhere in particular. These observations remind one strongly of Faber's experience with the mason-bees which, when their half-built nest was replaced by one that was finished, went on building until it was half again as high as it should have been. In Polistes it seems that the very success with which these first unfoldings of the feeding instinct meet, serves to stamp it into a useful habit. If the worker is at home, with the feeding larvæ at hand to seize the proffered bit, all goes well, and it becomes henceforth an efficient member of its community. But remove it, and so interfere with the normal unfolding of the reaction, and the wasp soon disregards the food altogether or contents itself with a few perfunctory turns and squeezes.

Not that the wasp has any idea of performing a service for the benefit of its kind. I have seen a young neuter gnaw a piece out of the side of a dead wasp larva fallen from its cell, and turning, offer it as food to the mouth of the self same larva. More than this, I once observed a neuter attack a live larva and, after she had cut out and crushed a fair-sized piece of its body, come back eight times in the course of her examination of the cells of the nest to this larva, which had naturally died in the operation, and offer it this part of its own body with the evident expectation that it would be seized and eaten. The eighth time she dropped the piece on the face of the dead larva and went away with an air of 'duty well done' which was comical to behold. There can be little doubt that the normal repetition of the reflex perfects it, so that finally the process is quicker and easier than at first; and in this sense the little worker learns, but thus far I have had no evidence that it gains anything by the example of its elders.

One other note on the feeding habit may be of interest. Throughout the social Hymenoptera the male is the drone of the colony and usually among the solitary wasps the work of excavating or otherwise constructing and storing the nest devolves entirely on the female. Mr. and Mrs. Peckham recount cases of cooperation of the male with the female of Trypoxylon to the extent of guarding the nest and even taking the spiders as they were brought by the female and packing them properly away. In one colony under observation this fall, the males eagerly took portions of dead larvæ from one another, and crushed and turned them in their mandibles; and, in one instance, when the malaxation was complete, one of them carried it over the nest in the same searching manner as the female, and finally fed it to a larva. This is the only recorded instance among the Vespidæ known to me, but it is likely further careful observations would show similar aberrations of instinct.

The Locality Study.

Several days usually elapse before the young Polistes makes its first essay into the world. When it does appear, the impulse to fly is strong, though in most cases it soon spends itself. That is, if in captivity, the wasp will repeatedly beat itself against its prison walls and steadfastly refuse to perform any of the reflexes it may have shown prior to this time. If at liberty, the impulse usually carries it a short distance, perhaps two or three feet from the nest, where it spends a considerable amount of time running about in an inquiring way. This alternation of short flights and strolls may last for an hour or more, and the wasp extends its examination of surrounding objects to some distance, before it returns leisurely and as if by accident to the nest. There is no such apparent purposefulness in the procedure as has been described for the solitary wasps.

The social wasps seem to fly because they feel like it, and the flight is not long because at first it is exhausting. Then follows rest and a stroll, because strolling is easier than flying; then, after another period of repose, perhaps another flight, until a period of this aimless wandering brings it back within reach of the distinctive odor of the nest, whereupon it returns to the accustomed place. Occasionally, the little wasp gets lost in these first casual ventures, and it is not improbable that some wasps become wanderers from the very beginning.

Unquestionably, being on the nest brings about a state of satisfaction analogous to that evinced by Mr. Thorndike's chicks when they had rejoined their mates. I have several times put a nest in a glass jar where wasps were confined, and when, after fifteen or twenty minutes' wild buzzing and running about, they accidentally came in contact with it, their behavior was, at once, entirely changed. They became quiet and observant, and soon showed a disposition to go on with their usual activities.

It is somewhat difficult to suggest to what this may be due. The nest has a faint characteristic aroma resembling that of wild honey, which becomes very perceptible when it is confined in a small space. Both the manner of using the antennæ and the behavior of wasps in which one or both of these organs have been excised indicate that sense perception by means of them is an important factor in orientation. Within certain limits, the odor of the nest may then serve to guide the wasp and modify its activities when it reaches home.

It may be profitable here to reflect on the factors of the extremely useful feeding habit. The whole appears to be a complex of reactions which are at first quite separate and distinct. The first step is the perfection of the process of malaxation and distribution of the food, and is taken before the wasp feels the impulse to leave the nest, or has had any opportunity of finding food for itself. Next comes the familiarizing with surroundings. This at first has apparently no relation to food-seeking, yet in course of time, and aided probably by the olfactory sense, the wasp naturally comes upon something edible, and, after extracting the juices, it may well be that it tries to distribute the food on the spot. This being impossible, there is a second alternative, that is, to fly, and, if flight takes it back to the nest, the rest of the procedure is probably carried out. Repetitions of this chain of actions causes it to occur oftener and with greater constancy, until the habit in all its complexity is well established.

It is well known that usually the wasp flies straight out from the nest, and does not return by the path it took in leaving. And while it appears that the first 'locality studies' are the desultory wanderings just described, there are nevertheless circumstances where Polistes makes the swift survey of the objects surrounding her nest, which has been described by Mr. and Mrs. Peckham for many of the solitary wasps. I observed this in numbers of instances where the wasps were set free after having been left in captivity long enough to habituate themselves to their new surroundings.

One nest with four workers was brought into the laboratory and established in a large glass cylinder, with a supply of food and weather-worn wood, so that they might go on with their activities if so inclined. They soon ceased their attempts to escape, and by the end of a week were attending to the wants of the larvæ in the usual manner. The glass plate from which the nest was suspended, was then moved to one side so as to leave an opening of several inches, but the wasps not perceiving this after several trials, the whole was carefully lifted out and rested on two supports, so that the wasp would find itself free if it flew six inches in any direction. Following is an account of a typical locality study transcribed from my notebook:

11:10. Freed nest (way already indicated). One of the wasps has flown out from the nest, hovers above it at a distance of twelve inches, and rising to the ceiling hovers there for some seconds. During the next six minutes descends to hover and circle within six inches of the nest, and, a second time, comes within two inches, without, however, alighting on it. First, flies round with its head directed toward nest, then turning, circles with its head away from the nest. This performance is repeated, and at 11:10 it alights on the glass, from the under side of which the nest is suspended, and for twenty seconds it beats its head against the glass. Rising, it explores first the upper, then the middle section of the room. Rising to the ceiling once more, hovers there and then descends to rest on glass as before. Spends several minutes exploring the room, and, returning, hovers for a few seconds before dropping upon the nest.

This is a fairly representative procedure, though there is great individual variation in the number and character of the circlings and the amount of search necessary in finding the nest after the more distant parts of the room have been visited.

Although no lengthy series of experiments was carried out with the same individual, those that were made show a decrease in the number and minuteness of the circlings proportional to the number of times the wasp so left the nest. The wasp never returned to the nest along the path by which she had left it. Experiments were also made by moving the nest as soon as the locality-study had been made, and seeing whether the wasp returned to the place where the nest had been. Invariably the wasp did return to the exact former site of the nest, but considerable variation was shown in the ability to find the nest in its new location. One wasp had no difficulty, when the nest had been moved a distance of eighteen inches; others were unable to do so if moved more than eight inches. In one instance, the site of the nest was changed while the wasp was sipping honey from a dish about fourteen inches away. Returning, and not finding its nest in the usual place, the wasp, in circling, reached the honey dish once more, and again started for the nest along essentially the same path. This was repeated eight times before the wasp in its explorations finally reached its nest and rested there. The whole performance looked as though the wasp were consciously using the honey dish as a landmark. It started out from this point each time, the same way as a person might, when he became aware that he was making some mistake in finding his way to a desired destination.

It would be interesting to speculate on the meaning of the various actions described above. What sense best serves Polistes in finding its way about? Does it actually see and make a mental note of the various factors of its environment? Or does a mere blind following in response to other sense impressions, namely, the olfactory, serve its purpose? Theory is fascinating, but with the slight data at command, it is hardly profitable. Observation shows that the wasp instinctively flies toward the light; its course is also materially affected by currents of air, such as draughts in a room where it is held captive. Mechanical response to these two influences will, in this case, usually serve to liberate it without the use of any other sense or faculty. Again, the antennae seem to play an important rôle in orienting the insect. Accidental loss of one antenna in one case retarded the finding of the nest. Further, the flight in circles, when leaving or approaching the nest, might be interpreted as due to the difference in stimulation of the antennae of the two sides—the side toward, and the side away, from the nest; and the flight straight to the nest, when the wasp has poised for a moment with both antennæ directed toward the nest, seems to add evidence in favor of this view. However, further experimentation is necessary before it is possible to attempt a satisfactory explanation.

During the cold days of autumn, when there are no more larvae to rear, about the only activity observed on the nest is that occasioned by the home-coming of a member of the wasp family. This one is tumultuously set upon by the half dozen wasps nearest him, each of which is favored with an embrace which is amusingly like the affectionate demonstrations shown on the return of a human being to his family fireside. Here, however, the attentions are lavished, not only on the newcomer, but on those who were the first to meet him, and plainly the meaning of the whole performance is simply the distribution of nectar by one of the wasps which has just returned from a foraging expedition. Earlier in the season, this nectar is regurgitated into the mouths of the feeding larvæ, but in their absence it is stored in the cells or serves directly as food for the adults.

Finally, I think the habits Polistes acquires may bear a decided relation to its rhythm of activity and repose. If we watch any wasp community, we see that periods of general sluggishness alternate with furies of activity and, in the case of the individual, any marked exertion is always promptly followed by great quiescence. Of course, what actually happens to the nervous system when impressions are fixed and habits formed is largely a matter of conjecture. But in the establishment of any reaction, it is generally thought that the repair of the nervous element is quite as important as the change which it undergoes while the reaction is taking place. And it would seem that the delicate nervous organization here implied would lend itself readily to the 'stamping in' of reactions or trains of reactions. That is, a particular performance, once called forth, would the more readily occur had a period of repose prevented the reception of any intervening impression and brought about the restitution of the nervous mechanism affecting the reaction in question.

The period of repose on the nest is usually terminated by one of the wasps starting up and commencing an examination of the cells of the nest. Others immediately follow suit, until the whole colony is in a tumult. But it is not the example of the first wasp that is responsible for this, only the external stimulus furnished the sleeping colony by the movements of the first wasp on the nest. Simple tests prove this. Godart relates how the colonies of Bombus have a trumpeter-bee, whose duty it is to rouse the colony to work in the morning. If this bee is removed, another takes its place the following day. An observer of a wasp colony might easily believe that similar duties had been delegated to particular wasps. But here, and probably in the case of Bombus, it is the fact that any external stimulus, such as a loud noise or jarring the nest, produces the same effect. The wasp examines the cells not because it is aroused to a sense of duty by seeing what the others are doing, but because this is the habitual response whenever it is gently stimulated while on the nest, by any means whatever.

In summarizing these observations, it may be said that, although they are perhaps hardly extensive enough to warrant definite conclusions concerning wasp intellection, they nevertheless indicate several things:

1. All wasps possess the instinct of fear. This is especially strong the first few days after emergence, but is readily overcome by the frequent appearance of the awe-inspiring object.

2. The feeding instinct is evidently called forth in response to olfactory impressions. These responses become more precise as they are repeated.

3. Once established, under favoring conditions separate reactions combine to form complex habits.

4. In a sense, the wasp remembers. This is indicated by the manner in which it accustoms itself to the sight of strange objects, and by its behavior when a change is made in its nest or surroundings.

5. It shows considerable individual variability, both as to time and manner of its response to stimuli.

6. Wasps do not imitate one another. Instinct and individual experience account sufficiently for their powers, and their apparent cooperation is due entirely to the accident of their being born on the same nest.

  1. The queens usually work singly, but in three cases two wasps were observed associating in the construction of the same nest. These may have represented a queen and a worker that had accidentally survived the winter. It is difficult to see how a partnership of queens could be formed, since the owner of a nest strongly resents the intrusion of another wasp, expelling her from the scene with the utmost ferocity.
  2. The careful researches of Siebold and Marchal show that even this function is assumed by the workers in case of the death of the queen.
  3. In writing a paper of this nature it is somewhat difficult to avoid misleading 'anthropomorphisms,' and it may be well to state once for all that the occasional use of expressions similar to the above is purely figurative and for the purpose of avoiding awkward circumlocutions.