IT may be convenient to consider briefly what ants are before dealing with their habits and their association with their surroundings and with other animals. Ants are all social insects and are polymorphic, that is, each species consists of several quite distinct castes. Except in certain parasitic species they are generally trimorphic, that is, they consist of three castes : (I) the male, usually winged; (2) the fertile female, or queen, usually winged until after fertilisation, when the wings are shed; (3) the more or less sterile wingless female, or worker, quite different from the queen. In many species the worker caste is divided into (a) soldiers, (b) workers, differing much in form, the soldiers often having the head and jaws disproportionately developed; and these sub-castes may be further subdivided.
Ants have complete metamorphosis, that is, the egg, larval, pupal and adult stages are quite distinct. The lame are legless maggots. The pupa? are either naked or enclosed in a cocoon. The objects popularly spoken of as ‘ants’ eggs ‘are really the cocoons. Ants occur everywhere, from the outskirts of the Arctic regions to the Tropics; from the timber line of the highest mountains to the plains and deserts; in forests, nesting up in the highest trees, and in swamps; underground and in caverns; in cultivated places, fields and gardens; in towns; in hot-houses and even in houses.
ANTS THAT HUNT AND TEND THEIR FLOCKS THEIR habits are very varied, and it has been suggested that they present a curious analogy to the hunting, pastoral, and agricultural stages in the history of human development. Some of them, for example, live chiefly on the produce of the chase, probably retaining the habits formerly common to all ants. They live the lives of the lower races of man, subsisting mainly by hunting. Dwelling in small communities, collective action is little developed, and they hunt and conduct their battles singly. Odiers live a higher social life; they are skilful in agriculture and have domesticated certain plant lice and beetles. They are thus comparable to the pastoral peoples
who live on the produce of their flocks and herds. They live in large communities and they know how to act in combination both in war and peace. Finally the harvesting ants and mushroom growers are comparable to the agricultural nations.
There are now no solitary ants, though the social ants are descended from solitary ones. The stages of the racial development of ants are as follows:
1. A pre-social stage with a single kind of male and female.
2. A social stage with a single kind of male and female, but the nesting and nursing instincts have developed.
3. A social stage with one kind of male and two or more kinds of female, all fertile, but those that build and hunt for food are becoming less fertile.
4. The present stage with usually one kind of male, a fertile form of female, and one or more so-called ‘sterile ‘females or workers. These workers, however, are fertile with sufficient frequency to maintain (principally through the male) a representation of their characters in the germ plasm of the species.
HOW AN ANT COLONY BEGINS
THE colony-founding of ants presents a number of problems. The subject has occupied the attention of many observers over a long period, but it has only comparatively recently been possible to give a connected account of the origin of the ant colony. Various experiments on colony-founding were carried out by the older writers on ants, but Lord Avebury was the first to prove that after their marriage-flight female ants were capable of bringing up their brood without assistance from workers, or from any other ants. It was subsequently assumed that all species of ants founded their colonies in this way. More recent experiments and observations have proved that although very many species found their colonies in this manner, other species adopt other methods.
The following list gives all the known methods by which a colony may be founded: I. (a) The female ant, after the marriage-flight, removes her wings, seeks a suitable situation where she constructs a cell and brings up her colony alone, (b) Several females voluntarily associate and found a colony in a similar manner.
II. The female seeks a nest of another species of ant, and is adopted willingly or otherwise by the workers who bring up her brood. In some manner, the host queen, if present, is eliminated. Then either (a), in course of time, the host colony dies out and a pure colony of the female species remains, or (b) the mixed character of the colony is kept up by means of slave-raids on nests of the host species by the female’s offspring.
III. The female is adopted into the colony of another species and lives side by side with the rightful queen. The intruder’s offspring of all castes, but only workers of the host species, are reared together in the nests.
IV.Differs from 11(a) only by the fact that the species of the alien queen having no worker caste, the colony only lasts for the lifetime of the host workers. Group I represents the normal method, and Groups II, III, and IV represent the abnormal methods.
Wheeler has recently carried Group I a stage further back, by observations made in Australia on rather primitive ants. He found that the female, after she has constructed her cell and laid her eggs, occasionally leaves the cell to forage for food, returning and closing up the cell again. It is a remarkable fact that an old queen, if removed from her nest, will carry out once
more all the necessary labours for the founding of a new colony, although she may have lived for years in her old nest, doing little except laying eggs and being fed and cleaned by the workers. In the case of Group I, an old queen will construct a new cell, lay eggs, and bring up her first brood as before; and one belonging to Group II will, if introduced into a nest of the host species, act in the same manner as she did when she was a young fertilised female.
Having given this general account of what ants are, and how they found their colonies, we will consider more closely a few of the very many striking facts in connection with their association with other animals, and with their environment.
ANTS THAT ARE FOOD STORES FOR THEIR FELLOWS THE true honey-ants live in Mexico and in the south-west of the United States and have long been esteemed as an article of food by the Indians. The best-known species is ‘The Honey-ant of the Garden of the Gods ‘—the Garden of the Gods being a place near Manitou, in Colorado. It may be as well before dealing with its dwelling-place and habits to consider what a honey-ant is and why it is so called. Many ants are in the habit of collecting honey-dew and storing it in their crops, which become distended. When they reach home, they feed their brood and the rest of the colony by disgorging the sweet liquid. Ordinary ants may often be seen returning home with the abdomen much distended.
Now in the honey-ants this habit has been developed until a class of workers has been produced which are called ‘repletes.’ Their bodies are enormously swollen; in fact, they are literally honey-pots. The size and rotundity of the abdomen are due to the crop, and not to the stomach. The former, being filled with honey, forces back all the other organs against the walls of the abdomen, which are stretched to their utmost capacity.
The ordinary worker is a quick and graceful creature, but the ‘repletes ‘or ‘honey-pots ‘are only able to waddle along. The replete form is confined to certain workers, and these are only formed when they are callows, that is to say, when they are newly hatched from the pupa into which an ant grub changes before it becomes a perfect insect. At this stage, the covering of the body is soft, but when the ants get older it becomes hard and they are unable to be formed into ‘honey-pots.’ This has been proved in observation nests in captivity, the callow being fed with maple sugar and other
sweet liquids. The callows greedily devour these foods, and some of them become semi-repletes, whilst others acquire the complete rotundity of genuine honey-pots.
It is chiefly the larger workers that act as honey-pots, but the smaller ones sometimes play this part. The ‘honey-pots ‘never leave the nest but store the sweet liquid fed to them by the other workers which go out to forage for food. In return they disgorge some of their store when the other workers wish to be fed. They are thus the living casks, or barrels, of sweet stuff, kept by the ant colony as a store in time of want. They live a quiescent life, hanging to the roofs of the subterranean chambers of the nest. They can move about a little, but should they fall from the ceiling, they are unable to return to their former position without assistance.
There are often as many as three hundred ‘honey-pots ‘in the chambers of a large colony. The nests are found on the top of the stony ridges in the Garden of the Gods and in other suitable localities. The large circular entrance to the nest is in the centre of a cone-shaped crater composed of small pebbles. A gallery goes down into the ground and is divided into smaller ones. These lead to underground chambers which have smooth, flattened floors and rough vaulted ceilings. The ‘honey-pots ‘hang from these ceilings side by side, and the irregularity of the roof enables them to hold on by their claws.
The workers are nocturnal in their habits, and do not go out during the day. A guard, however, is set at the doors of the nest to prevent other ants, or spiders, etc., from forcing an entrance. About half-past seven in the evening, the workers leave the nest and visit the thickets of slim oaks which are in the neighbourhood. The twigs of these oaks are covered by roundish galls caused by a small four-winged insect, and at night these galls exude drops of a sweet, watery fluid. These drops are eagerly sucked up by the foraging ants, and when they return home they feed the repletes with the contents of their crops. The galls probably provide only a portion of the ants’ food, and no doubt a large quantity of their honey is obtained from the scale insects and plant lice which occur on the oaks and on other plants in the neighbourhood.
INSECTS THAT SELL THEIR SERVICES TO ANTS THE relationship between ants and other creatures with which they associate, or which associate with them, is of two kinds—active and passive. In the first instance, the ants
actively seek out their guests; in the second, the ants are themselves passive, and are sought out by their guests. As instances of the former, one may mention the relationship between ants and plant lice, scale insects, the caterpillars of the blue butterflies, etc. The ants milk and obtain a sweet and nutritious secretion from these creatures, and in return the latter obtain protection from enemies and often shelter as well.
The ants seek out these guests on their food plants, and some they bring back, keep and rear in their nests. One of the most important items in the menu of many kinds of ants is obtained from plant lice. They are insects which possess a long, delicate rostrum with which they pierce the integument of plants and suck up their juices. They are well called ‘ant cows,’ as ants both milk and breed them, keeping them in herds and building sheds for them, and walls to protect them. The liquid which the ants obtain from these ‘cows ‘is voided in colourless drops, and contains a fair proportion of sugar. When voided on to the leaves of plants, it is called ‘honey-dew.’ Some species of ants lick it off the leaves, but others actually milk the plant lice. They stroke them with their antenna;, when a droplet is exuded, which the ants suck up.
Many of the plant lice possess two tubes which are situated on the top of the back near the end of the body. It has been incorrecdy stated that it is from these tubes that the droplet is obtained, and indeed many textbooks on entomology repeat this error. It is, however, from the extremity of the body that the sweet secretion is supplied. The tubes contain a thicker and more sticky substance, and this is used by the ‘cows ‘to protect themselves from the ‘aphis-lion,’ the larvae of the lady-birds, and other insects which prey on them.
HOW THE ANTS BRING UP THEIR ‘COWS’
SOME ants collect the eggs of plant lice when laid and keep them in their nests during the winter. When the eggs hatch, the ants carry the young plant lice out of the nest and place them on their proper food plants. These eggs, which are covered with a thick, black membrane, may often be found in large numbers in ants’ nests. Of the underground species which live on roots, many are only found in ants’ nests, and some of the yellow subterranean ants live exclusively on the excreta of root aphides. When winged forms of these species are hatched in the nests, the ants clear a way for them to allow them to escape into the open.
When an ant’s nest which contains subterranean aphides is disturbed, the hosts will be seen to pick up the ‘cows ‘and carry them down the galleries into safety. A large grey species with a long rostrum lives under bark in company with a brown tree-ant. It generally has the end of its very long proboscis buried in the wood of the tree, and it is with considerable difficulty that it can be removed without breaking the proboscis. However large they may be, when there is danger, the ants drag and jerk at them unmercifully to make them leave go so that they can be carried off into safety. Plant lice produce vast quantities of ‘honey-dew,’ and it is not surprising that ants should have found out their value, and utilised them as cows.
Let us now consider the case of the ‘Honey Caterpillars,’ the caterpillars of the ‘Blues ‘(Blue butterflies) which are attended by ants all over the world. The ants milk the caterpillars as they do plant lice, attending them on flowers or leaves where they may be feeding. The caterpillars possess an unpaired gland in the middle of the back of the eleventh segment, which can be protruded through a transverse slit. The ants caress the posterior end of the caterpillar with their antenna; until it emits from the gland a droplet of colourless sweet liquid which is eagerly imbibed by the ants.
The benefit gained by the relations between the larvae and the ants is marked, for the latter obtain a sweet secretion, of which they are very fond, and the caterpillars are protected by the ants against their natural enemies. Some of the caterpillars are carnivorous and feed on the ants’ aphides and scale-insects, and even in some cases on the ants’ brood. An Indian species, when it is in the butterfly stage, attends aphides, stroking them with its long front feet, and sucking up the secretion emitted with its proboscis. These observations suggest the existence of three-cornered relations between ants, the ‘Blues ‘and plant lice.
The caterpillar of the ‘Large Blue ‘is an instance of the caterpillar feeding on the brood of its hosts. The caterpillar feeds on the wild thyme, and when it leaves its food plant, it wanders about until it meets, or is met by, an ant. The ant will then probably milk it, or perhaps other ants may come up and do so. But it is always the ant that finds the larva first which carries it into the nest.
After milking the caterpillar, the ant walks round about it, and eventually some sort of signal is given by the ant, or by
the larva, when the latter hunches itself up into an extraordinary shape—the head is much retracted, the middle of the back swells up, and the posterior part becomes very narrow in consequence—and the ant seizes it about the middle and carries it into her nest. There the caterpillar does not appear to attract much attention; it seeks the chamber where the ants’ brood is thickest and rests among them. It devours very many of the ants’ larva; and grows very rapidly. When full grown it spins up, pupates in the galleries of the nest, and the perfect butterfly emerges in June.
THE MENACE OF THE UNINVITED GUEST
A RELATIONSHIP wherein the guest is uninvited and merely tolerated by the host is the truer form of insect hospitality, and is more in the nature of parasitism, often being harmful to the hosts. When the guests seek out the ants, they may be friendly, indifferent, or actually hostile to them. They live in the nests for many different reasons; for protection, shelter, warmth, or food. Some feed on the ants themselves, or on their brood; others live on the excreta, food or prey of their hosts. They are always seeking their own advantage, although at the same time they may supply a sweet secretion of whicli the ants are fond, or they may act as scavengers in the nests. The following biological division of the regular ants’ guests may be noted:
1. The True Guests: these receive true hospitality from their hosts, being fed or licked, or both fed and licked, by the ants.
2. Indifferently Tolerated Lodgers, which are tolerated for various reasons, and stand in many kinds of different relationships to their hosts.
3. Hostile Persecutor Lodgers, living as beasts of prey and murderers in and near the nests, and devouring their hosts or their brood.
4. Outer and Inner Parasites living and feeding on, or in the ants, their brood, or their guests.
As an example of a ‘true guest,’ we can select a beetle which passes its whole life in the home of its hosts, the blood-red, slave-making ant. The beetle is fed by the ants and supplies them with a sweet secretion which exudes from small orifices in the segments of the hind body. It is reddish brown in colour, with tufts of golden hair covering the places from which the sweet fluid springs. When it wishes to be fed, it taps an ant with its antenna; in the same way that one
ant does to another when asking for food, and the latter feeds it from its crop.
A near relation of this beetle, also a true guest, has gone a step further. It not only uses its antenna? when supplicating its host, but also strokes the ant’s cheek with one of its front legs, which is what an ant would do under these circumstances. The beetle can also feed itself, for when kept in captivity in observation nests it has been seen to bite at dead ants and to suck caterpillars and other creatures given to the ants as food.
This beetle is not very ant-like in appearance when examined by itself, but when it sits among a lot of its hosts—and it is always found where the ants are thickest—it becomes practically invisible. The reason for this is that the light which is reflected from the concave sides of the thorax of the beetle appears to the eye like the narrow back of an ant, and the rolled-up hind body of the beetle reflects the light in the same way as the rounded hind body of a fat ant.
When their hosts change their nest or move from place to place, these beetles move with them. They can also fly, as they possess ample wings, wrapped up under their short wing-cases. The courtship takes place in May, and the female, who is viviparous (I.e. brings young larva; direct into the world), deposits her offspring on the egg-masses of the ants. The young grub proceeds to feed on the brood of its hosts. The ants not only feed it by mouth (this can be proved by feeding the ants with honey coloured red or blue, when the colour can be traced in the intestinal canal of the little larva through its transparent skin), but they place it on their own larvas.
The beetle larva is very like that of the ant, and though it possesses six short legs, it does not use them, but imitates the behaviour of an ant larva. The ants pay it the greatest attention and when danger threatens the nest they carry it first into safety. It is extremely voracious and devours large quantities of the ants’ grubs. The larva? change to pupa? in the galleries of the nest, and they are often killed by the ants carrying them about as they do their own cocoons. This serves to keep the beetles in check.
THE INDIFFERENTLY TREATED LODGERS
THERE are very many species of indifferently treated lodgers, with many different habits; many act as scavengers; some pass their whole lives in the nests of their hosts; others pass
only the earlier stages there. A certain beetle, which is superficially like a lady-bird in appearance, is an example of the latter case. The perfect insect is found on trees and shrubs overhanging and near the nests of the ‘Wood-ant ‘which builds its hillocks of pine needles, etc., in pine and other woods. It also occurs on the wing in the neighbourhood, often in company with a large lady-bird, both species resembling each other.
Its life-history is briefly as follows. The beetle seeks a tree or shrub above or close to the wood-ants’ nest and drops her eggs on to the ground beneath. Each egg is covered by a case, or capsule, which is formed around it by the female and consists of her own excreta. This covering is placed in position with the hind feet, the egg being held in a depression of the abdomen. The covered egg exactly resembles a small bract, and is also exceedingly like the end of a birch catkin.
The ants pick up the covered egg and carry it into the nest. The larva, which hatches in about twenty-one days, uses the egg-covering as a nucleus on which to build the larval case, and while very young carries it about fixed to the posterior end of the case. The egg-case has a threefold reason d’etre—to protect the egg and newly hatched larva, to attract the ants by its resemblance to a bit of useful vegetable refuse, and to give the larva a foundation on which to start the larval case. When the larval case grows larger the egg-case may be found embedded in it; or it may be broken off. If this should happen the larva fills up the hole with the same material as that with which it builds the rest of the case. This material, which it prepares with its jaws, consists of its own excreta mixed with earth.
To enlarge the case the larva removes particles from the inside and plasters them on to the outside. The object of the case is, of course, to protect the larva from the ants. The larva feeds partly on vegetable refuse in the nest, but also on the droppings and pellets of the ants. During its moults the larva fastens the case to some object in the nest. When full grown it fixes the case to a piece of wood, or twig, and turning completely round changes to a pupa with its head facing the broader end of the case. The perfect beetle emerges from the case by biting a circle inside it and thus forming a detachable cap, which it forces off. After this, it escapes from the nest. It then seeks a mate and the courtship takes place on trees, etc., near the ‘wood-ants’ ‘nest.
SINISTER GUESTS THAT ROB AND KILL
THE Hostile Persecutor Lodgers are mostly beetles with short wing cases; some are very like their host ant, and are confined to one host; some have two hosts and live with one species in the winter and early spring, and with the other in the summer. All these beetles prey upon ants, lurking in the ‘runs ‘of their hosts, and in corners of the nests, and falling upon and murdering solitary individuals. When disturbed they curl up and pretend to be dead, remaining motionless for some time. They are also protected by well-developed repugnatorial glands, which emit a gas or vapour possessing a strong, pungent smell. If a beetle is attacked by an ant it pokes its tail in the ant’s face and gives off this vapour, when the ant falls back and the beetle is unhurt.
As an example of an Outer Parasite the larva of a little fly which lives in the colonies of an ant in Texas may be mentioned. Its small larva clings to the neck of an ant larva by means of a sucker, and encircles its host like a collar. Whenever the ant larva is fed by the workers the fly’s larva uncoils its body and partakes of the feast. Sometimes, when there is no food in reach, the larva will tweak with its sharp little jaws the sensitive hide of a neighbouring ant larva, or even its own host, till the ant larva squirms, and by wriggling incites the worker-ants to bring a fresh supply of food. When the ant larva spins its cocoon it encloses the fly larva within its web. The fly larva pupates beneath the host, but the host hatches first, and the apparently empty cocoon is thrown on the refuse heap. The fly emerges from its puparium and escapes from the cocoon by the opening made by its host.
There are also a number of curious mites which attach themselves to different kinds of ants’ bodies. In connection with this it is very interesting to note that two specimens of an ant, closely related to a living species, have been found in the Baltic amber, each of which bears a large mite attached to the ventral side of the base of the left hind shank. The close similarity in the position of the two specimens suggests that these mites had already acquired the habit, so remarkably developed in some of the recent species, of attaching themselves to very definite regions of the hosts’ bodies.
The mites called ‘antennas bearers ‘are very good examples of this. They exhibit most interesting parasitic relations with their hosts. They are partly true guests as
they are fed by the ants, and partly outer parasites as they are always attached to the ants’ bodies. The feet of the three pairs of hind-legs are provided with suckers, with which the mites can hold very tightly to the ant, and are not easily dislodged. They wave about their long pair of legs, which are directed forwards, and look like antenna;.
The usual position for these creatures is on the chin of the ant. Sometimes, however, two or more will be found resting on a single ant. The positions taken up are either on the chin and forehead, or on each side of the head, or on the hind body. They are always arranged symmetrically in order not to upset the ant’s centre of gravity. Six specimens may, very rarely, be found attached to one ant, when they fix themselves as follows : one on each side of the head, one on the chin, one on each side of the hind body, and one on its upper side.
When a mite resting on the ant’s chin wishes to be fed it scrapes the mouth of the ant with its front legs, and the ant disgorges a drop of fluid, which the mite sucks up. These mites are often fed by other ants besides the one on which they happen to be. They will solicit another ant for food and the ant immediately feeds them. When an ant which bears a mite is fed by one of its fellows the mite leans forward and shares in the meal. These mites often transfer themselves to the young callow ants soon after they have emerged from their cocoons. The callows often try to get rid of them, falling on their backs, rolling on the ground, and rubbing their chins against anything handy. The mites, however, dodge about on the ant’s body out of harm’s way, and eventually the callow becomes reconciled to its fate.
Besides the four-winged parasites, and certain flies (two-winged creatures) which lay eggs in an ant’s body where their young are reared, the nematode worms are the best examples of inner parasites. Some of these worms live in the glands in the head of ants, others in the abdomen. Those worms which live in the crops of the larval, pupal, and adult workers of certain foreign ants, produce a great distension of the host’s abdomen in the adult stage. They enter the larva; and by unduly stimulating their appetites cause them to be fed to excess so that they grow very large and a gigantic worker form is produced, having various female characters.
It is a larval form of the worm which enters the ants’ larva;. Sometimes the worms emerge from the host after death, when they bore out through the lower part or end of the hind
body. They cannot emerge and live on dry ground, but on very wet ground they quickly emerge and bore into the earth. This accounts for the presence of parasitic colonies living on or near damp places. As many as two worms will sometimes be found in the abdomen of a single ant. When the worms become adults, which takes place some time after leaving the host’s body, very many eggs are formed—some twelve thousand for each worm—and are laid in the larval skin of the worm.
ANTS THAT USE THEIR YOUNG AS SEWING-MACHINES ANTS in four different genera have developed the habit of using their larva, literally, as sewing-machines, to construct their nests. The first mention of these nests in literature is to be found in Captain Cook’s Voyages. He observed the nests of one of these ants in the branches of the mangroves in Northern Queensland, Australia. The passage, of course, only refers to the nests and not to how they were constructed.
Nests are made in the following way. The ants select a cluster of leaves, and pull them together in a very ingenious manner. Ants stretch across the gap between two leaves, and catching the edge of one with their jaws and of the other with their back legs, they pull them together until they meet. Whilst some of the ants hold them together, other ants appear with their larva? in their jaws and apply them to the edges of the meeting leaves. Whenever the larva touches the leaves it deposits a thread of silk. The ant moves it from side to side, touching it against first one leaf and then the other, and thus the leaves are stitched together. The process is repeated with other leaves until the nest is completed.
Small nests occur, but the largest may be nearly as big as a football. Inside, the nest is divided into compartments made with leaves and silk, and contains the ants’ brood, workers, sexes and prey. These ants also construct ‘cattle-sheds ‘of a few leaves to house their scale insects, etc. When a queen founds a colony she lays her eggs in a curled-up leaf and uses the larva?, when they hatch, to spin together a few leaves and thus start a nest. They kill and devour large quantities of other insects, stretching them to death.
These ants possess long waists and hold on to each other by them to form chains to stretch over large gaps. It has been suggested that their long waists have developed as a result of their habit of stretching across gaps. This theory is strengthened by the fact that the species found in the Baltic
amber have a considerably shorter waist than the species existing at the present time. The writer also found this to be the case in the fossil specimens from the Gurnet Bay deposits on the Isle of Wight.
ANTS THAT GROW MUSHROOMS AND CARRY ‘SUNSHADES’ THERE are a certain number of ants which are mushroom growers, and use cut-up leaves as a substratum on which to grow the fungus. Some are called ‘parasol ants ‘on account of the habit they have of carrying the large round pieces of die leaves they have cut off trees over their heads, when they return with them to the nests. The excavations for these nests are very extensive. Chambers are constructed deep down in the ground, one above the other but with some little distance between them, and they are connected by tunnels and galleries.
The mushroom gardens are usually grown on the ground of the chambers, but in some cases they are hung from the roofs. The fungus garden consists of a mass of chewed-up leaves covered with a white fungus. It looks like a number of tufts of wool. The ants do not allow the hypbas of the fungus to grow to mushrooms, though if left alone, the fungus will become an ordinary-looking common mushroom. The hyphse are only allowed to produce small, round, white growths called bromatia, and on these the ants feed exclusively.
All the different species of mushroom growers cultivate a different species of fungus; no other species is allowed to grow. It is only the smaller workers who cut up the leaves in the nests and cultivate the bromatia. The larger workers go out along regular paths to shrubs and bushes which they mount, and snip out with their sharp and powerful jaws large circular pieces from the leaves, often entirely defoliating a tree. For a long time it was uncertain what use the ants made of the leaves. It was suggested that they were used to thatch the roofs of the underground nests, or even as food. Belt, in Nicaragua, was the first to discover that their real use was as manure on which to grow the fungus gardens.
FOUNDING A COLONY: HOW THE VEGETABLE GARDEN IS SOWN THE colonies of these ants often consist of very large numbers of individuals. A colony is founded by a young fertile female in this way. After the marriage-flight she
removes her wings and constructs a small underground cell. She then spits out the pellet from her infra-buccal pocket. This pocket is a spherical cavity situated below the pharynx, and forms a receptacle for the solid and semi-solid parts of the food rasped off by the ant’s tongue, and also for foreign matter scraped off the ant’s body by its tongue and strigils (the spurs on the front legs). Any juices that remain in these substances are extracted and sucked into the pharynx, the residue being ejected in the form of a solid body, the pellet, which retains the shape of the infra-buccal chamber.
After this pellet has been ejected it must still contain a considerable amount of nutritious matter, for it forms the chief, if not the only food of the larva? of a genus of flies and also part of that of some beetle larva?. Moreover, Wheeler discovered that in the larva? of all four genera of one of the sub-families of ants the swollen front or ventral portion of the first abdominal segment, just behind the mouth, forms a pocket in which the workers place the pellet from their own infra-buccal chambers. No other ants have been observed to feed their larva? in this way, but eventually spit the pellet out.
The pellet in this instance contains hypha? of the fungus, some of the substratum of chewed-up leaves, the scrapings from the female’s body, etc., and with it she proceeds to cultivate a small fungus garden, manuring it with her fa?ces. She lays eggs, some of which she breaks up and plasters over the mass; others are allowed to hatch in it. The young larva?, when hatched, feed on the fungus growth, and eventually pupate. When the young workers emerge they tunnel through the earth of the cell to the open air, and collect pieces of leaves which they bring back to add to the fungus garden. The latter is now only attended to by the workers, and the queen devotes herself to egg-laying. The colony increases in size, other fungus gardens are started, and eventually a very large colony, occupying a large extent of ground, is formed.
THE GRANARIES OF THE ANT CITIES: PROVIDING FOR A ‘RAINY DAY’ IT was originally recorded by the ancients that ants stored seeds in granaries to serve as food in time of scarcity. This was doubted in the early part of the last century, being regarded as a fable, or myth. Later, however, the fact was thoroughly re-established, and it is now well known that a
variety of ants of many different and distantly related genera do harvest seeds for food. It can be readily understood that in hot, arid countries where insect food may be lacking, or very scarce for many months in the year, and where competition with other insect-eaters may also be very keen, it would be of great advantage to ants to become, in part, vegetarians. Moreover, carnivorous ants possessing powerful jaws for crushing the hard integuments of their prey are well fitted to deal with seeds.
In many of the harvesting ants the larger workers, or soldiers, have enormously developed heads to support the powerful muscles by means of which their large jaws are worked. These workers are literally living ‘nut-crackers ‘for the rest of the community, and they crush up the hard seeds when required for food. At the time when these large workers are of no further use to the colony the other ants cut off their heads and throw them on the refuse heap—a very drastic, but effective, method of getting rid of a superfluous working-class.
As stated above, it is now established without doubt that many ants do collect grain and store it. When damp, they bring up the seeds to dry, in order to prevent them from germinating, and if any seeds sprout they gnaw that part away. Moreover, ants play no small part in the distribution of plants, as even in England several ants collect seeds which they carry home. Many seeds get dropped by the way, and thus give rise to plants at some distance from their original spot. The agricultural ant of Texas has been stated, however, not only to collect seeds of a plant called ‘Ant-rice ‘but actually to plant and cultivate them, and gather the seed next year. The seed resembles the grain of oats, and tastes like rice.
The ant itself is of a rusty red colour and possesses, in common with many species that live in deserts and dry ground, a beard of long curved hairs. It is able to endure prolonged droughts. The nests of this ant are variable in construction according to the nature of the ground on which they occur, but they are always fully exposed to the sun. They generally occur among the herbage, and all plants growing on or around the nest are cut down and a flat area or disc is cleared for ten or twelve feet round. Should a growing tree be near they move the nest, or else strip all the leaves off the tree.
WHERE ANTS MAKE ROADS AND WEED THEM ROADS five inches broad near the nest but narrower farther from it are made through the herbage for hundreds of feet in different directions, and these roads are weeded and kept as bare as the disc. If the soil be of a gravelly nature the ants use the gravel to build a cone or crater in the centre of the disc about three feet high, which is sometimes surrounded by a low mound, two or three feet in diameter.
There may be from one to five entrances to the nest. The nests are perforated beneath with flat chambers, some of which form the granaries and are connected by galleries. The granaries never occur deeper than two and a half feet, but the galleries may reach a depth of fifteen feet. Some of the bits of gravel which form the cone are of immense size and weight as compared with the ants. Although they also feed on insects and on other seeds, the ‘ant-rice is the only plant allowed to grow in a circle round the nest, and all other plants are cut down as soon as they appear. This rice is regularly sown before the wet season, and about November 1st the young green shoots spring up; the seeds ripen in June of the next year. The ants carefully weed and attend to these plantations, and gather the seeds. When the seeds have been harvested, the stubble is cut down and removed. The ants throw away the chaff and refuse and, if damp, the seeds are brought up to dry.
A colony is founded in the following manner. The marriage-flight of the bright red females and darker males takes place at the end of June or the beginning of July, after which the female, having removed her wings, digs down into the earth and closes up the opening. She gradually brings up her first brood of some twelve very small, timid workers. In the spring the workers open up the nest, but are careful to conceal the entrance with small pebbles and bits of stick which look as if they might have been brought together by the wind. It is not until the second year when the large workers are produced that the ants begin to cut down the vegetation around the nest and establish the circular discs. These discs increase in size as more workers are produced.
The discs are evidently for the purpose of ensuring as much dryness as possible, to help to prevent the germination of the seeds. The grubs of the ants are fed with portions of crushed seeds, which the workers first coat with saliva to
ensure that the starch contained in the seeds is converted into sugar. The sting of this ant is exceedingly painful.