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F. sanguinea with those of the continental Polyerger rufescens. The differences are very remarkable; the latter can neither build, migrate, colleet food for its young ones, nor even feed itself; hence it is absolutely dependent upon its slaves for everything ; without slaves, that species must become extinct. Formica sanguinea gives the orders to its slaves, determines when and where a new nest shall be made, and when they migrate the masters carry the slaves; in Switzerland the slaves collect aphides for their masters and go out with them; in this country, the slaves of this latter species generally remain within their masters' house, and the masters get less work out of their slaves than they do in Switzerland.
* By what steps the instinct of F. sanguinea originated I will not pretend to conjecture. But as ants, which are not slare-makers, will, as I have seen, carry of pupa of other species, if scattered near their nests, it is possible that such pupæ originally stored as food might become developed, and the foreign ants thus unintentionally reared would then follow their proper instincts and do what work they could. If their presence proved useful to the species which had seized themif it were more advantageous to the species to capture workers than to procreate them--the habit of collecting pupæ originally for food might by natural selection be strengthened and rendered permanent for the very different purpose of raising slaves. When the instinct was once acquired, if carried out to a much less extent even than in our British I', sanguinea, which is less aided by its slaves than the same species in Switzerland, I can see no difficulty in natural selection increasing and modifying the instinct-always supposing each modification to be of use to the species-until an ant was formed as abjectly dependent on its slaves as is the Formica (Polyerges), rufescens.' (Origin of Species, p. 223.)
The relation of ants with the plant-lice or aphides and the gall-flies is one of the most curious points in the history of the ant; and here again it is Huber who first gave us the best and fullest information on this subject; he showed that the aphides are the domestic milking cows of the ants, and that they are kept by them for this purpose. The aphides “fix themselves upon the leaves and small branches, and insinuate their trunk or sucker between the fibres of the bark, where they find the most substantial nourishment. A portion of this aliment "shortly after being taken, is expelled, under the form of small • limpid drops, either by the natural passage or by two horns
that we commonly observe in the posterior part of the body. * This fiuid constitutes the principal support of the ants. . .
They wait the moment the aphides eject this precious manna, Enpon which the ants immediately seize; but this is the least of Geir talents, for they know how to obtain it at any time
they wish. (P. 210.) M. Forel has satisfied himself by direct observation that this sweet fluid proceeds from the natural passage, and not from the two well-known horn-like projections at the lower extremity of the aphis; these latter also secrete a substance, less fluid, however, than the sweet liquid drops. When unattended by ants the aphides by a certain jerk of the body throw out this fluid to a distance, but when ants are present, watching the moment of emission, they suck it quickly down. But ants possess the power of making the aphides yield their sweet drops at their pleasure. Huber shall tell us in his own words how the ant thus milks its cow. an ant at first pass some aphides without stopping or disturbing them.
• It shortly after stationed itself near one of the smallest and appeared to caress it, by touching the extremity of the body alternately with its antennæ, with an extremely rapid movement. I saw with much surprise the fluid proceed from the body of the aphis, and the ant take it in his mouth. Its antenna were afterwards directed to a much larger aphis than the first, which, on being caressed after the same manner, discharged the nourishing fluid in greater quantity, which the ant immediately swallowed; it then passed to a third, which it caressed like the preceding, by giving it several gentle blows with the antenne on the posterior extremity of the body; the liquid was ejected at the same moment, and the ant lapped it up. It then proceeded to a fourth; this, probably already exhausted, resisted its action. The ant, who in all probability knew it had nothing to hope for by remaining there, quitted it for a fifth, from whom it obtained its expected supply. It now returned perfectly contented to its nest.' (P. 213.)
It appears that this tapping with the antennæ is a constant preliminary to the emission of the fluid, and that the aphis voluntarily submits to the operation, giving greater facility for the ant's taps by lowering the head. Should the aphides remain long unmilked by the ants, they deposit their fluid upon the leaves, where the ants find it on their return; the aphides never resist the solicitation of the ants when in a state to satisfy them. This curious alliance, as Forel remarks, between the ants and the aphides consists of an exchange of good services, for the ants protect their cattle against numerous enemies, such as the larvæ of the ladybird beetles ( Coccinelle), and of some of the Diptera as the Syrphus. Some kind of ants are in the habit of transporting their cows from one place to another. The greatest
cow-keeper of all, perhaps, is the yellow ant (Lasius flavus). This ant is more decidedly a stay-at-home species, and likes to have all its conveniences within reach; it never goes far from its abode, and does not search the trees for aphides or any kind of food; it is a small yellow ant, the neuter being scarcely two lines in length, and is abundant anywhere, raising its little mounds which carry off the rain from its dwelling, in orchards, meadows, or heaths. Huber tells us that these yellow ants are extremely jealous of the aphides, often taking them in their mouths and carrying them to the bottom of the nest, or bringing them to the top. We cannot wonder at this when we learn that this aphis secretion is the little ant's only source of food. Huber placed some of these yellow ants in a glazed box with their aphides upon some soil; he also placed with them some growing plants, which he watered occasionally, so that there was no lack of food
"The ants made no attempt to escape; they appeared to have nothing to desire; they took care of their larvæ and females with the same affection as in their own nests; they paid great attention to the aphides and never injured them; the latter did not seem to labour under the slightest fear; they allowed themselves to be carried from place to place, and rested in the spot chosen by their guardians. When the ants wished to displace them, they began caressing them with their antennæ, hoping thereby to induce them to abandon the roots or to withdraw their proboscis from the cavity in which it was inserted ; they afterwards took them up gently in their mandibles, and carried them with the same care as the larvæ of their own species.' (P. 225.)
But it is not only the aphis itself, whether young or adult, that the yellow ant takes care to introduce within its nest; the eggs of the aphis are eagerly sought for and brought home. We call the little oval-shaped bodies which may be found adhering to various plants in the autumn - eggs' for convenience sake, but really they are not eggs at all in the true sense of the word. It is well known that the aphides produce young ones without the intervention of the male sex—this was shown by Bonnet in 1745, and has been repeatedly verified; that for many months these young aphides are all females, they in their turn being virgin mothers capable of reproduction; these are produced alive and undergo no metamorphosis. In the late autumn or early winter, however, innumerable quantities of small, often black oval, bodies are produced; so that it would seem that we have a combination of viviparous generation at one season, and of oviparous generation at another, in the same insect. But this is a mistake: the socalled egg is a nymphal form of aphis, which differs in no respect from the ordinary nympha whilst yet within the body of the parent, excepting that it is enveloped in a covering. Gould noticed these little black bodies in ants' nests, but wrongly thought them to be ants' eggs which would produce
females; there is not the slightest doubt, however, as to their true nature. Huber calls them eggs,' but it is evident that this most accurate observer held the opinion—first, we believe, expressed by Bonnet—that they are young enclosed in a covering or cocoon, This covering is nothing more than an asylum, of which the aphides born at another season have no need; it is on this account some are produced naked, others "enveloped in a covering. The mothers are not then truly 'oviparous, since their young are almost as perfect as they ever
will be in the asylum in which nature has placed them at their birth.' (P. 246.) We have over and over again satisfied ourselves that this is the true nature of the so-called aphis eggs. If these eggs are collected in the late winter and brought into the house, they will after a time shrivel up, thus showing that the contained aphis is dead. Bonnet vainly attempted to preserve these bodies alive in his room till the following spring; he considered that they died from want of proper moisture. We know that in the natural state when adhering to various plants out of doors, these aphis-cocoons, at the return of spring, burst their membranes and countless thousands of the insects are produced. That Bonnet was correct is curiously enough shown by the behaviour of the yellow ant towards these captured aphis-cocoons.
Huber again shall tell us the story: Speaking of this species of ant (Lasius flavus) the fourmi jaune of our author, he writes
. On opening the ant-hill I discovered several chambers, containing a great number of brown eggs; the ants were extremely jealous of them, carrying them away, and quickly too, to the bottom of the nest; disputing and contending for them with a zeal that left me no doubt of the strong attachment with which they regard them. Desirous of conciliating their interests as well as my own, I took the ants and their treasure, and placed them in such a manner that I might easily observe them. These eggs were never abandoned.' (P. 244.)
So much for the jealous care with which these aphis-cocoons meet with from the ants. In a former passage (p. 232) Huber says that the ants approached the eggs,
slightly separating their pincers, passed their tongue between them, extended them, then walked alternately over them, depositing, I believe, a liquid substance, as they proceeded. They appeared to treat them exactly as if they were eggs of their own species. It appears, then, that ants know everything that is necessary to the preservation of these eggs; they pass their tongue constantly over them, and invest them with a glutinous matter, which retains them together. They, in consequence, are preserved until the period when the aphides quit them; they employ, then, the same means to preserve their cows, if I may use this expression, that M. Bonnet supposed would preserve these eggs, and secure their disclosure in the spring.' (P. 246.)
If, therefore, we may regard the aphis as the cow of the ant, we may, perhaps, be justified in considering its cocoon as the calf.
There can, we think, be no doubt that the curious relationship existing between ants and aphides is the result of mutual service. The aphis yields its sweet secretion voluntarily for the benefit of the ant; the ant confers a benefit on the aphis by removing from it the viscid secretion. This latter supposition is rendered probable by the fact that if the ants do not come to relieve them, the aphides deposit their juices upon the leaves of trees or elsewhere; and this is conformable to Mr. Darwin's belief, ' that the instinct of each species is good for itself, but 'has never, so far as we can judge, been produced for the ex
clusive good of others. Certain gall-insects, as well as the aphides, supply some ants with a similar secretion, as has been witnessed by Huber, Forel, M. Delpino, and others. Huber compares the movement of the antennæ, in this case, to the play of the fingers upon the keys of a pianoforte.
Aphides and gall-insects, in Europe at least, are the great food-providers for ants, but M. Forel says that the differences in this respect are enormous according to the species of ant.
' Leptothorax is never seen to carry the aphides; it is the same with Pheidole, Tapinoma, Hypoclinea, and A. structor, as I think these ants have other means of subsistence; some are more carnivorous than others, as Pheidole, Tapinoma, Tetramonium; others directly lick the juices of flowers and of trees (Leptothorax, Colobopsis); others, again, store up grains, which they cause to germinate in part so as to supply them with sugar (A. structor). Some kinds feed exclusively on aphides (L. flavus, L. brunneus), or nearly exclusively (L. niger, Camponotus). Others know how to vary their means of subsistence, to lick flowers, to kill insects, to rear aphides; such are all the species of the genus Formica. The genus Lasius exhibits great variety in this point of view. The species flavus and umbratus rear only the aphides of roots [aphis radicum ?]. L. fuliginosus only pays attention to the aphides of the bark of trees; L. niger and alienus those of bark and the outer part of plants. They also know how to transport these latter from one place to another. In fine, L. emarginatus only takes a few of the aphides, and only those found on the surface of plants. (Forel, p. 421.)
M. Forel, like Huber, has never seen an ant kill or injure an aphis. M. Duveau, on the contrary, has seen an ant in the act of tearing and devouring an aphis; but such conduct on the part of an ant is probably quite exceptional.
Leaving the subject of ants and their milking cows, we need