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Insects in ant colonies


Insects in ant coloniesThat "no man liveth to himself" is an aphorism not to be questioned in human communes. That no community lives to itself is equally true. And this applies to ants.

Their societies are established in the vicinage or in the midst of numberless creatures, most of them, like themselves, free citizens of that wild life which nature has organized and maintains in the cul­tivated parks and fields of men no less than in a wilderness.

He deludes himself who thinks that he ever is delivered from the environment of wild things. Of the large and grosser sorts, it may be; but civilization never will tame or exterminate the innumerable hosts of minor creatures, seemingly as wild now as in the primitive Eden, that inhabit our day-world and, even more, our night-life.

The ants are examples of this. They find and keep a foothold everywhere. I have surprised immense communities in the heart of great cities. I have shown an American farmer, who boasted in the tilth of his acres ­ under the plough since the first English settlements ­ that he could scarcely put down a foot in a walk through a field without placing it upon a little commune of meadow ants.

These cases do not stand alone. A naturalist would soon point out to our farmer that many other living things have possession of his domain whose ancestors were probably here before Columbus, and whose descendants will doubtless outlive the Republic. These are, the creatures with which ants have to neighbor.

Close neighbors they are at times; sometimes hostile, sometimes indifferent, sometimes friendly. In the course of ages of neighboring experience, strange interrelationships have been established, presenting some of the most interesting and puzzling features of emmet communal life. To a few of these our attention will now be turned. Taking up once more our mountain mound-builders, we note certain loose relationships established between them and some other insects in cold weather. Winter deadens energy and subdues combativeness, and, when severe, suspends activities. One will then come across colonies of our common white ant (Termes flavipes) imbedded within the great cones of Formica exsectoides Bunches of cockroaches are found, and sundry beetles, with other insects, that in the adult or larval stage naturally domicile in the ground.

Most of this sort of neighboring is the result of that truce which Jack Frost enforces, and will largely disappear when spring relaxes nature and insects come to their normal antagonisms. But it shows how certain companionships may have been formed which, at first accidental and temporary, were found to be harmless, more or less helpful, and in some cases highly beneficial. Use and heredity, operating upon casual affinities and the acquisition of a common nest-odor, may have thus brought about those examples of symbiosis, or sympathetic companionship, which exist among ants, and between them and other creatures.

Let us consider a little more in detail this theory that winter conditions may have influenced the formation of communal affinities and associations between ants and alien insects, as well as between separate species and genera of ants. Do the facts seem to justify it? One night, while encamped among the ant hills of Brush Mountain, Pennsylvania, late in August, there fell a heavy frost that well disclosed the effect upon ants of such temperature changes.

At 3.45 A.M. I made the round of the hills, and found their inmates in a state of semi-torpidity. Tapping the surface and stamping upon the surrounding stones, which heretofore had always brought out a host of workers, failed to arouse a single sentinel. I dug into one mound eight inches before finding ants, and these showed little activity - a marked contrast with their usual mode.

Then the aphis feeding-grounds were inspected. A white-oak tree near a stone wall, whereon numbers of aphids were domiciled, was a popular emmet resort. Mounting the wall, I turned the lantern light upon the overhanging boughs. The aphids were in their places on the leaves and branches, surrounded and covered by groups of ants. But all were semi-torpid. The frost had surprised them at their feast, and left them frigid upon the spot. Many of them had abdomens distended by crops gorged with honey-dew, which showed translucent as the light fell upon them. In my long experience of a full generation in observing emmet ways, I recall few more striking visions than that. If one could only have preserved those congealed specimens for the museum! But as the sun returned with his wonted August fervor, the statuesque groups began gradually to dissolve.

First, with sluggish movements, slowly stirring; then more vigorously, as the sunshine fell upon the branches; until by nine o'clock the tree-paths were thronged with workers, most of them repletes, and homeward bound. As the sunlight pierced the woods, and fell upon them and warmed them up, they resumed their normal activity. The benumbing effect of the frost upon the insects had been no doubt intensified by its suddenness, and the high temperature that had preceded it.

The above facts led me to studies of the winter condition of the mound-makers, which were made late in October, and the latter part of February. It was found that the winter tended to drive alien insects to the formicaries for harborage. Lodged in one nest was found a colony of our native termites. They were in an unfrozen part, exposed to the sun, occupied a space of about four inches square, and were then (February 14th) quite lively. Near them was a large herd of roaches, a hundred or more. The ants in the mound were not torpid, although their characteristic vigor and activity were suspended. It would not have been possible for the termites to hold such a position in midsummer; they would have been eaten.

Such a cluster of cockroaches would have been equally impossible; it would have been scattered and destroyed. This is doubtless the general experience. Wheeler found that in Texas, during autumn and winter, the nests of Formica gnava teem with alien insect guests of various orders, larvae and adult, that are rarely seen in summer.

How shall we account for this? In the case of the mound-making ants, there seem to be two factors, one negative and one positive, in drawing termites and roaches to the nests. The first is the benumbing effect of cold, which suspends the emmet energies, and there ­ with suspends hostile acts toward intruders upon their domain. The second is the greater warmth and com­fort of the mounds. These are built of a light composite of soil-pellets and pine and other leaves, which form more congenial quarters than the surrounding earth. The galleries that honeycomb them are air­chambers which mitigate the cold and conduce to natural warmth.

Besides, to errant insects abroad in the autumn in search of winter quarters, the upraised cones of the ants are prominent and inviting objects, the most available. for them in the vicinage. So there the rovers settle and stay until, in the revived activity of returning spring, the ants make the premises entirely too warm for them.

These facts have at least a conjectural bearing upon the origin of some ant affinities and associations. The importance of the local nest-odor, and its intimate relationships with the friendly or hostile attitude of ants toward their follows, has already been pointed out. May it not follow that the temporary and accidental lodgment of these alien insects upon the ants' nests may have led, in occasional cases, to the acquisition of so much of the local nest odor as partly to conciliate the ants? This complaisance may have been increased by the inactive condition of the ants in early spring, and at least made them tolerant of the presence of their guests. This condition, acting upon temperaments specially adapted to such an estate, together with the discovery of some mutual advantage in nourishment or massagerie, through the shampoo dejeune or other
wise, may have developed at last into the habits of the permanent myrmecophile. This may be suggested, at least, as a contributory factor in the natural, evolution of a remarkable feature of ant communes.

A brief observation will illustrate the advantage which some of the alien ant guests find in the connection, and which must strongly tend to hold them to it when once formed. Certain little crickets of the genus Myrmecophila live with species of Formica and Camponotus, and a diminutive, nearly blind cockroach (Attaphila fungicola Wheeler) inhabits the nest of the Texas cutting ant. The behavior of these myrmecophiles shows that the surface of the ant's body must be covered with an unctuous, highly nutritious, and, it may be, antiseptic secretion, probably derived from the salivary glands of the host-ant or other members of the colony. This secretion is also spread over the eggs, larvae, and pupae, and it seems to retard the development of pernicious moulds, since these tend to grow only on the larvae and pupae that have been isolated for several days from the workers and queens.

Both crickets and cockroaches live by licking the surfaces of their hosts. The former remain on the ground and reach up to lick the legs and bodies. The latter climb upon the backs of the large Atta soldiers and feed from that position. The ad­vantage to the ants may be simply the pleasure of the massage and the satisfaction of being clean, although there may be other advantages now unknown. How­ever, we shall presently see that such affinities and associations may exist even under strong disadvantages apparent to human observers, at least.

Among the ant-loving (myrmecophylous) beetles found with our Alleghany mound-builders is a Claviger species (Tmesiphorus costatis) collected during the winter. Doctor LeConte showed me, in his rich collection of Coleoptera, several of these taken at Bedford and Columbia, Pennsylvania, among which were Cedius ziegleri LeConte, and others which he spoke of as "undescribed specimens of Homolata and an unnamed species of Oxyopoda." These were small brownish insects with slight pubescence.

The most interesting of these ant-affinities (myr­mecophiles) was his own species, Xenodusa (Atame­les) cava. This is a reddish-brown beetle, about one-fifth of an inch long, with tufts of yellowish hair-like tubes on the sides of the abdomen. From these hairs exudes a sweet secretion upon which the ants feed, as upon the honey-dew of aphides, and it is this fact which attracts ants to them or assures their toleration of them. Specimens of this beetle were also taken by or for LeConte in ant nests of unknown species in Maryland, Illinois, and Michigan. Among these was one still held in its host's mandibles, as if taken while in flight from the disturbers of its nest, and clung to with unrelaxed jaws in the alcohol which killed it.
Our American carpenter ants (Camponotus) in several species and varieties are often the hosts of X. cava. All the beetles of this group, the Lomechusa group of Staphylinids, are true ant-guests. They are treated by their hosts, both as adults and larvae, quite as their own fellows, being fed, cleansed, and carried about. Indeed, it is said that in case of real or fancied danger, the beetle larvae and pupae have precedence of their own young in the ants' attention.

This is all the more remarkable because, according to Father Wasmann (S.J.), a devoted and distinguished observer, and perhaps our highest authority on myr­mecophilous insects, these adopted citizens repay the host's care by ravenous assaults upon their own brood, devouring numbers of eggs and larva. The effects of this, in weakening the commune, are apt to be serious. It works toward deterioration, as Wasmann shows, in another way. This brood - parisitism appears to originate a curious form of abortive individuals intermediate between the female and the worker, known as pseudogynes. They are cowardly and indolent. They decline to dig and nurse, and trot about the nest aimlessly. Thus, in sharp contrast with the valiant and active workers, they hold a sort of "frustrate existence."

How comes this about? Wasmann believes, and seems to prove, that it is caused by the diminished care and diet due to the queen larvae for their full development - a case of restricted growth through defective nourishment. A brood of beetles (Lomechusa) begin life with a brood of worker-ants. The beetle larvae, as they appear, are not only generously fed by the ants, but begin to feed upon their eggs and larvae; and as they are extremely voracious and grow rapidly, they devour enormous numbers. This makes a great breach in the generation of coming ant-workers. These are essential to the commune, and the adults aim to make up the lack by converting into workers some of their larva, destined for queens. This results in that intermediate form, neither worker nor queen, but a spurious female - a pseudogyne.

At the same time the infatuated ants, under the impression that their guest-larvae are valuable to the commune, lavish on them care due to their own progeny. Thus, again, arises a neglect of the young ant queens which stays their growth, and diverts their development toward the pseudogyne. It is the old story of the cuckoo among the birds, who thrusts her egg into another bird's nest, and secures for her parasitic offspring the nurture due the legitimate fledglings.

It might therefore be maintained, with a good degree of verity, that social men in their communal life show no great superiority to social insects in dealing with the parasites that infest them. Especially when we consider the vast advantage of men over ants in natural endowments, the relative unwisdom of the latter does not bulk so largely.

A Chalcid fly, Orasema viridis, is parasitic upon colonies of the ant Pheidole instabilis. The chalcid is a beautiful insect, decorated with metallic green, and blue, violet, yellow, and black, with iridescent wings. This polychromatic creature, when seen among its ruddy hosts, amid the shining red and black seeds stored for food (the ant being a harvester), gives a brilliant appearance to the nest. But it is a beauty which bears the germs of death to those who cherish the possessors.

The mother Orasema posits her numerous eggs upon the under surface of bodies of the young ant near the head. She chooses for this the pupa, of the large forms-soldiers, females and males-not the small workers, as having the richest store of nutriment. Here the parasites cling and grow rapidly, feeding upon the juices of their host. When the parasites reach the pupal stage - within two or three days-they are released by the worker-ants from their host, now a lifeless mass.

Thenceforward they are objects of special care by the Pheidole workers, who tend them as their own offspring, not only in the pupal, but in the imago stage. Indeed, so great is this infatuation or delusion that, as in the case of the Lomechusan beetles, when a nest is disturbed the Orasemas are looked after before the ants' own brood!

The life cycle of Orasema from egg to imago is a week or ten days. Thereafter the adults are licked and fondled and borne about by the ants, and fed by regurgitation. The guests commonly take these attentions passively; but sometimes - just as growing boys resist embraces - seek to avoid them. One cause of difference between hosts and parasites emanates from the preference of parasites for free air, which, as soon as they mature, both sexes aim to reach. Their hosts, having different views as to the relative values of light and darkness, guard the exit gates, and, seizing their guests, drag them back to the dark inner rooms.

This tendency of the Orasemas results from their natural habit of mating in the open air, after which the fertilized females seek a Pheidole nest wherein to start a new brood upon the round of parasitic life above described. After pupation the mature Orasemas spend much of their time lying on their sides among the, ant larvae and pupa. They contribute in no manifest way to the welfare of their hosts, their only interest in them being the selfish one of securing nurture for themselves and a brooding host for their offspring.

One finds nothing in the life history of insects more puzzling than such seeming anomalies as the above associations between ants and parasitic chalcidids and beetles. We are used to some such social phenomena among men, who seem to have a perverse strain that forces their development along aberrant lines toward disadvantageous and destructive ends. But in these simpler children of nature such conditions surprise us as quite abnormal.

Once in a while, however, the ants do seem to shake off the spell that binds them and awake to the true nature of their guests. In one of Professor Wheeler's artificial nests of Pheidole instabilis the workers rose upon the adult Orasemas, after they had remained in the nest several days, and killed and dismembered them. But a doubt remains as to whether this was due to their discovery that the victims were predatory aliens, or to some special stress of hunger or other cause; for the ants also killed and dismembered their own females, and after that reared only their fellow-workers and intermediates, as though they purposed to spare none but the caste that furnishes the lightest consumers and the helpers, and to free themselves from mere dependents. Like action on the part of worker-ants of other species has been known in times of special stringency in the food supply.

Another of the parasitic aliens that associate themselves with ants is a little Dipteron fly, Metopina pachy­condylae Brues. While sorting out a number of larvae of a large black Ponerine ant, Pachycondyla harpax, several were found to have larvae of the above insect attached to the region of the first abdominal segment. It quite encircled the ant larvae, like a collar about the neck, "a kind of Elizabethan ruff." The posterior end of the parasite was provided with a sort of suction disk, by which that part could clasp its host so tightly that the fore part of the body could be released and swung out of position without the creature losing its hold.

The experimenter transferred a colony of the ants to an artificial nest for observation, and fed them with a number of young larva, of the ant Camponotus maccooki. These the Pachycondylae proceeded to tear to pieces, freely lapping the exuding juices. Then they placed the pulpy remainders in the ventral surface of their own larvae (as on a serving-dish), which lay upon their backs in a chamber dug in the earth of their nest. This chamber was so situated under the glass cover that the actions of both ants and larvae could be observed distinctly. The ant larvae thrust out their brown heads and began to feed.

The Dipteron larvae, by some unknown sense made conscious of the presence of food, unloosed their heads and necks without releasing their caudal attachment, and dipped their beaks into the mess. Thus the two young creatures so widely apart in structure and destiny were here united in their cradle­life and became fellow-trenchermen.

The experiment was repeated a number of times, and with various sorts of food. The result was always the same. To quote the picturesque language of the observer, he was always "able to witness the strange banquet - the dwarf reaching from the shoulder of the ogre, and helping himself from the charger formed by the trough - like belly of his host." Pieces of ant larvae, beetle larvae, myriapods, etc., when served up to the Pachycondyla larvae, were partaken of with equal zest by larval host and guest. The latter were thus shown to be true commensals - "perhaps the most perfect commensals, in the original sense of the word, to be found in the whole animal kingdom."

As a bit of by-play, we learn that when the ant larvae lay close together a Metopina would reach over and help itself from the portion of a neighbor, keeping the while its rear attachment. Sometimes, when the rations were exhausted, the Dipteron would nil) the tender hide of a nearby ant larva till it squirmed with pain, or it would tweak its own host. The suggested purpose of this action was to attract the attention of the nursing workers to the wriggling ant larva, and thus prompt them to replenish the larder.

Both kinds of larvae were cleansed by the nurse-ants, who, if they were conscious of the presence of the parasites, made no discrimination between them and their hosts. Indeed, as this species of ant is almost blind, it seemed doubtful if they really could distinguish larval host from larval guest, the latter possibly being taken for a mere enlargement of the former's neck.

One hesitates, however, to accept a theory which implies such a lack of sensitiveness in the perceptive organs of insects commonly so highly developed. However, as ants are notoriously devoted to the genuine antennal "tone" of society, and as the Metopinae, from the egg onward, are imbued with the true Pachycondyla atmosphere, the distinction between the two larvae might readily be lost in the common odor. Yet this would equally account for their sparing the guest, even though its nature were perceived.

The next stage of development in the life history of these strange yoke-fellows is equally interesting. When the ant larva is mature, and nature stirs within it the great unrest that precedes transformation, it sets its spinning glands in motion, and begins to weave around itself the brown cocoon, or closed silken sac, within which the change occurs. It moves back and forth, around and around, issuing from the mouth-parts the liquid silk that hardens about its snug house of change until that is complete, when it falls into the quiet of pupation.

What becomes of its Dipteron yoke-fellow during these movements? Surely they could not be wrought with that encumbrance upon it? No; it has disappeared. Whither? The mystery was solved by opening an ant cocoon. Therein lay the Metopina safely and snugly tucked away in its own little puparium lodged in the posterior pole of the cocoon. It had dropped off its host's neck, had taken station close by the opposite end, and had been wrapped within the silken sarcophagus. Thereto it had attached itself, had wrought out of its own larval skin an envelope (it is not a spinner like the ant), and in that it pupated. The quarters were large enough for both occupants.

Now follows another interesting chapter in our story of these humble lives. Duly the time comes when Nature bids the transformed antling break forth from its silken coffin. It makes with its mandibles a rent at the anterior pole, favored, it may be, as with other species, with the obstetrical aid of worker nurses. It creeps out, and, though still a callow, is soon numbered arnong the active members of the commune. The empty cocoon case is carried by the workers to the common dumping - ground for waste products of the commune.

But what, meanwhile, has befallen Metopina? In the struggles of the antling to get out, and from the cutting and tearing of the nurses to deliver it, has the young Dipteron escaped injury? Fortunately it so "happens" - if that be the lawful word - that its puparium is in - variably formed at the posterior pole of the ant cocoon, directly opposite the anterior pole from which, as the point next to its jaws in its recumbent position, the antling emerges, and to which, as the point of fracture, the strain and force within and without are directed. Thus the little squatter sovereign, in its tiny putparium, goes scot-free and quite unharmed to the communal kitchen-middens, along with the abandoned cocoon of its yoke-fellow.

So it befalls that, as Professor Wheeler quaintly puts it, "after a privileged existence as free pensioner and bedfellow to a generous host, it is unwittingly carried away in the wornout bedclothes and consigned to the family ragpile." Here one must note another admirable "happening." The period for the Dipteron to emerge falls later than that of the ant. Therefore its hatching - place is the emmet dump where it has been deported by its foster­mothers, the ants. Fortunately for the newly fledged insect, since nature has not furnished it with fit implements to break through such formidable walls, it finds a wide and effectual door already open in the tough cocoon. It is once more debtor to its sometime host for that hospitality which not only "welcomes the coming," but also "speeds the parting guest," and crawls out of the rent made by the emerging antling. Thenceforth its new world lies before it.

It finds its mate. It follows the mysterious impulse of its kind, and returns to the commune whence it came, or flies to some other colony of Pachycondyla harpax, and, mousing among the robust larvae thereof, drops its minute egg. But there our story of the cycle of her life must end.

And what a wonderful story it is! Here, if ever, one may apply Marlowe's phrase: "Infinite riddles in a little room." It has taken the patience, skill, and experience of the trained naturalist to trace it and unfold it to us. But it needs no expert to note the admirable adaptations by which a minute fly has been borne on, step by step, in utter helplessness, through the successive stages of a dependent being, from a mere speck of vital matter to a winged insect, armed with the instinct to invade an unknown world and propagate its kind. How great and how infinitely exact must be that Over-Force that dominates nature, which can include within the compass of laws that regulate the universe a series of adaptations like these which guard the life of a two-millimetre parasitic fly!

It amazes, while it perplexes one, to account for it all. Yet, in the face of great Nature's workings, one may venture to recall the proverb of Spenser (not Herbert, but he of the Faerie Queene) : "Ill can he rule the great who cannot reach the small."

In contrast with our studies of the chalcid Oraserna viridis and the beetle Xenodusa cava, it is pleasing to record that the association between Metopina the fly and Pachycondyla the ant is apparently wholly benign ­ at least, under ordinary conditions. The guest does not prey upon its host; no physical injury seems to follow its enforced companionship; and the bare particle of food filched from the ant larva does not tax the supply­department of the commune or cause its workers to stint their own dependents. The larval hosts themselves are as large and healthy as others in the nest, and produce normal pupae. It is a case of "all's well that ends well."

These are but types of numerous examples of those strange and seemingly "unnatural" companionships with alien creatures which have grown up in ant communes. The literature thereof is already large, and is continually growing as entomologists push their investigations more widely and carefully. It would be impossible to present here an abstract of even a tithe of the known facts, but from the typical ones which have been chosen the reader may fairly judge of the general tenor of the rest.