|Standard Cyclopedia of Horticulture|
Ants, Their Habits, Activities, Injuries and Control. Various kinds of ants are troublesome to gardeners; and all the ants are most interesting animals.
The ants belong to the same great group of insects (Hymenoptera) that contains the wasps, bees, sawflies, and others; and like the honeybee and common wasps are congregate in their habits of living. The abdomen of all the common ants is attached to the thorax by a slender waist, or peduncle; and each segment (there may be one or two) of this peduncle is expanded on the top side and forms a lens, or button-shaped knot, a character that distinguishes ants from all other insects. Everyone is familiar with ants; they occur in all lands and all regions, from the dry deserts to the damp forests, from the timber line of mountains to the lowest valleys and among the dwellings and habitations of man. They seem to thrive in all kinds of environment and multiply enormously, so that they outnumber all other terrestrial animals.
The nature of an ant colony.
Ants are social; that is, they live in colonies or communities where every individual ant works for the good of the whole and not for itself alone. A colony of ants furnishes an illustration of a more perfect communistic society than any ever established by man, and perhaps a more amicable one than any he will ever be able to organize.
In a typical colony of ants, there are at least three kinds of individuals, the queen, the males, and the workers. The queen is not the ruler but the mother of the colony. Her only business seems to be to lay eggs which hatch into workers and other forms to take the places of those that disappear or die, thus maintaining the full and continuous strength of the community. When the queen comes forth from the pupal stage, she has wings which she retains until after the swarming period. After the swarming flight is over and the queen alights, her wings fall off or arc torn off by herself or workers and from that time she remains wingless. In some species of ants there may be modified forms of the queen, for example, giant queens, dwarf queens, worker- like queens, and other forms.
The males, which have wings, exist only to mate with the queens, and after the swarming period is over they eventually die. The males are also often modified into giant males, dwarf males, worker-like males, and other forms.
The workers, which are undeveloped females, are wingless and constitute the great majority of individuals that we see running about in the vicinity of an ant-nest. The workers are just what their title implies. They do the work of the community, build the nest, keep it clean, care for and procure food for the queen and larvae, care for the eggs, fight the battles, and so forth. The workers may exist under several different forms. One especially interesting form has a very large head and strong jaws, thus fitting it for war-like functions. Ants of this form are known as the soldiers.
The nests and activities of ants.
The nests of ants, in a general way, consist merely of a system of passageways or cavities communicating with each other and connected to the outside world with one or more openings. There are some species of ants that live below the surface of the earth and have no openings from their nests into the air, except at the swarming period. The style of construction and the materials used by ants in making their nests vary with the different species and with the environment in which the animals live. Moreover, the nests are very irregular, especially when compared with those of wasps and bees.
The passageways of the nests are enlarged here and there into comparatively large cavities, or chambers. It is in these different chambers that the activities of the colony are conducted. The queen lies deep within the interior of the nest in a dry, dark chamber. Here she is carefully tended and fed by the workers who bear the eggs as they are laid, to other chambers and zealously care for them. Many insects never see their young; others may see them but do not care for them; others, like the bees and wasps, put food into the gaping mouths of their young but have no further association with them. The ants, however, stand alone among insects in their very intimate relations with their progeny from the egg to the adult. Some of the chambers in the nest are reserved for the eggs, some for the larvae, and some for the pupae. If, as often happens, the eggs, larvae and pupae are all in one chamber, then they are each grouped by themselves in separate piles, reminding one, as Lubbock says, "of a school divided into five or six classes." In the simpler and more primitive ants, this grouping and separation may not be Bo distinct. The ants are constantly transferring their young from one part of the nest to another in search of the right degree of moisture, temperature, and the like. In the warm part of the day, the young will be transferred to near the surface but at night will be carried down again away from the cool air. The ants are constantly cleaning the young, caring for the eggs to prevent mold from growing on them, helping the callow ants to emerge from their cocoons, bringing food, cleaning, enlarging and reconstructing the nest and doing thousands of things contributing to the comfort, growth and happiness of the community.
The relation of ants to plants and to insects.
It has been argued and many observations have been offered to show that there is a most intimate relation between ants and many kinds of plants. Certain observers think that many plants not only offer special inducements to attract ants to them by affording favorable nesting-places, but also offer the ants delectable food in the way of a sweet liquid, the floral and extra- floral nectar. In return for the domiciles and the food, the ants are supposed to protect their plant hosts from certain insect and other animal enemies. In other words, the relationship is one of mutual benefit, or a symbiotic one. It is certainly true that many species of ants make their homes in the hollow stems of plants, in the thorns of acacias which the ants easily hollow out (see Bull-horn Acacias), in cavities in bulbs, leaves, and so on, and in the dried seed-pods of plants. It is also true that ants assiduously collect and carry to their nests the sweet nectar excreted by many plants. It is not so clear, however, that these favorable nesting- places and the nectar are provided by the plants on purpose to attract the ants, nor is it clear that the ants afford the plants protection from their animal enemies. In other words, more definite proof is needed to show that the relation between ants and plants is a purposely mutual one.
On the other hand, the relation of ants to plant-lice, tree-hoppers and certain scale insects is clearly, in many cases, a mutually helpful one. Especially is this true of the relations between ants and plant-lice. The aphids secrete a sweet liquid material known as honey-dew, of which the ants are very fond and which they are active in collecting and carrying to their nests. It can hardly be supposed that the aphids excrete the honey- dew solely for the ants. The liquid is an excretion from the alimentary canal and is exuded whether ants are in attendance or not. On the other hand, ants are very solicitous in their care of aphids in return for the honey- dew. The ants sometimes build "sheds" over the lice for their protection and sometimes take the lice into their own nests to care for them. In the case of the corn-root louse, the ants collect the eggs of the aphid in the fall, carry them into their own nests, and care for them all winter. In the spring, the newly-hatched aphids are carried out by the ants and placed in burrows dug beforehand among the roots of certain early food-plants. Later, the ants excavate burrows along the roots of the corn and transfer the aphids to these plants.
It is interesting to watch the ants collecting the honey-dew from the aphids. An ant approaches a louse and gently strokes the latter with its antennas, whereupon the aphid exudes a drop of the sweet material which is quickly gathered up by the ant. This action may be repeated with three or four of the aphids until the ant has all it desires, when it hurries down the stem of the plant and away to its nest with its load of sweet provender.
The life-history of ants.
Enough observations have now been made to enable us to say that most, if not all, colonies of ants are started by a solitary queen or occasionally by two queens working together. The queen, after the swarming period, alights, breaks off her wings, and digs a burrow in the soil or in decayed wood, forms a small chamber, and then closes the opening. Here she remains until her eggs are laid and have hatched into small larvae that finally mature into normal but diminutive workers. All this time the queen has taken no food but has lived and fed the first workers on the reserve material in her body. The small workers now begin to enlarge the nest and soon other larger workers are reared and the community begins to multiply and increase.
The eggs laid by the queen are small and white and rarely seen by the ordinary observer. These are solicitously cared for by workers and finally hatch into white, footless, soft, grub-like larvae. The larvae are also tenderly cared for by the workers and changed from chamber to chamber in conformity with variations in temperature and moisture. The workers feed the larvae either on food which has been predigested and which the workers now regurgitate, or on bits of dead insects, leaves, or seeds that have been chewed fine. The larvae finally, after attaining their growth, change to whitish pupae which, in some species, are inclosed in cocoons, while in others they are not. These the workers treat with the same solicitude and care that they show toward the larvae. The pupae are often mistaken for eggs. Often, on raising up a flat stone, one will see the workers running this way and that with the larva; and pupae in their jaws, evidently seeking a place of safety for them. The pupae finally transform to the adult ants of the various forms, workers, queens, and males.
Economic importance of ants.
Ants, as a whole, may probably be considered as agents in making the earth more habitable for man. Some of the species are neutral, perhaps, in relation to the economic status of mankind. A great many species are certainly beneficial through their action in stirring and aerating the soil. They are constantly burrowing deep into the earth and bringing up the particles which they distribute over the surface. Their action in this respect is similar to that of earthworms, the value of which was revealed to us by the classic investigations of Darwin. Ants are also important agents in aiding in the decomposition of organic substances. Their work in this respect is little appreciated or realized because it is invisible. It must be remembered, however, that this work of ants is gradual, incessant, and extends through tremendously long periods of time.
Again, ants are great insect-destroyers. Their food consists, in great part, of the juices and tissues of dead insects or insects that they kill. The interesting driver ants of the Old World and the legionary ants of tropical Africa pass through a territory killing and devouring multitudes of living insects, rats, mice, and the like. Hunter and Hinds tell us that there are twelve species of ants known to attack the immature stages of the Mexican cotton boll-weevil. "In some cases more than half of the immature stages in fields have been found to be destroyed by ants alone. To find 25 per cent so destroyed is not a rare occurrence."
On the other hand, certain household species of ants are very annoying and troublesome. Moreover, the leaf-cutting ants of tropical America are very injurious to plants. They will strip a fruit tree of its foliage in a very short time. One species of these leaf-cutting forms (Atta texana) found in Texas, attacks cotton, corn, fruit trees, sorghum and other plants, and has become of considerable economic importance. In some places, land is not planted on account of fear of attack by these ants.
The mound-building prairie ant (Pogonomyrmex occidentalis), distributed over a large part of the western plains of the United States, has become a distinct pest since man has begun to occupy the prairies. Its large mound-nests in fields of alfalfa or grain become serious obstacles to harvesting the crops. Moreover, when the nests are disturbed, the ants emerge in large numbers and attack man and beast, inflicting painful wounds with their stings. In dooryards and lawns and along paths, they are liable to attack the passerby, especially dawdling children.
The agricultural ant (Pogonomyrmex barbatus molefaciens) of Texas may build its mound-nests in fields of alfalfa, corn, or cotton, and, since it allows no vegetation to grow over a considerable area around the nest, the injury may be serious. Moreover, they are pugnacious and sting intruders severely.
Perhaps the most injurious role assumed by ants is their protection and fostering of plant-lice, scale insects, and the like. Aphids and scale insects arc among the most injurious insect pests, and anything that protects them or aids them in increasing may l>e considered an enemy to man. As a pest, the Argentine ant (Iridomyrmex humilis), stands by itself. Professor Newell says, "As a household pest I venture the opinion that this ant has no equal in the United States.
Unfortunately, it has also become a serious menace to horticultural interests as well. It destroys the buds, blossoms, and fruit of certain plants and protects and fosters certain scale insects that are very injurious to sugar-cane. Moreover, it has in a few instances actually shown itself to be dangerous to human life by nearly suffocating young infants.
The Argentine ant was probably first introduced into the United States through the port of New Orleans, and is now found in Louisiana, Mississippi, parts of California, and probably Texas. It is an exceedingly tenacious ant, holding on where once established, increasing with great rapidiiy, and driving out all the native ants.
The termites, or white, ants.
The termites are not true ants. In fact, they stand at the opposite end of the insect-world, widely separated from the ants just discussed. They resemble the true ants, however, in many important respects. For example, they five in great colonies, and many tropical species build large mound-like nests. Moreover, in each colony there are several kinds of individuals, for example, the queen, the males, the workers which are blind or have imperfect vision, and, finally, the soldiers.
The food of termites usually consists of dead or decaying wood, and the species in the United States live mostly underground or in old logs, in the timbers of buildings, or in the walls and floors of houses. Occasionally they injure young pecan and orange trees by mining into the stems and sometimes attack sugarcane. The greatest injury performed by termites, however, is by burrowing into the sills and foundation- timbers of buildings, thus undermining the whole structure. They also injure books and documents stored in damp basements and sometimes become serious pests to greenhouses.
The control of ants in gardens, lawns and fields.
The only method of getting rid of ants permanently is by locating the nests and treating them in such a way that the queen will finally be destroyed. The substance most used for treating the nests is carbon bisulfide. One or more holes should be made in the nest with an iron bar and an ounce or two of the liquid poured into each hole. The openings to the holes should be quickly and tightly closed with a clod of dirt. A heavy wet blanket thrown over the nest will aid in retaining the gas and tend to make the fumigation more effective. The liquid evaporates and the gas penetrates the whole nest, killing queen and workers, thus exterminating the colony.
Within the past few years, several workers have used potassium cyanide with good success in destroying ants in the field. J. D. Mitchell conducted experiments against the leaf-cutting ant in Texas. He dissolved the cyanide at the rate of one ounce in one quart of water and poured a quart into each of the openings of the nests. In every case the colony was destroyed by one or two applications. This method may be followed to advantage in destroying ants in gardens and on lawns, but the solution may be made weaker—one ounce of the cyanide to two to four quarts of water. Best results will be secured by using 98 per cent pure potassium cyanide. It must be remembered that this is a deadly poison and great care should be exercised in handling and storing it.