Life among the ants

The peculiar symbiotic relations between ants and aphids is worth a brief description. The aphids or plant-lice live in colonies upon certain plants, and feed upon juices which they suck from the foliage. The liquid excrement of these insects is sweet, and a surprisingly large amount is voided—Bŭsgen found that the maple aphid produces as many as forty-eight drops in twenty-four hours. This substance is sometimes so abundant that it covers the leaves and even drips down to the ground; it is known as honeydew, and some rustics still believe that it somehow falls from heaven. The ants are very fond of this honeydew, and some species live upon it almost exclusively at certain seasons, and locate their nests always near good aphid-pastures. The ants never kill and eat aphids as they do other insects, but protect them against their enemies. They even carry them about from one pasture to another, and some species build little sheds and corrals in which their aphids are confined just as we confine cattle. Sometimes the ants simply lap up the honeydew as it falls upon the leaves, but in most cases they milk the aphids by gently stroking them with the antennae, which causes the emission of a drop of the sweet liquid. Some kinds of aphids have developed a circle of stiff hairs around the anal opening, which thus retains the honeydew till the ant comes for it. Not only do the ants care for and milk the adult aphids, but they rear them from the eggs. Huber, Lubbock and others have seen ants collecting aphid eggs in the Autumn, and it has been found that these eggs are stored in the nest until they hatch, when the young plant-lice are carried out and placed on a suitable food-plant. On cold or rainy days they are taken back into the nest; when the weather moderates the ants carry them out to pasture again.

The scale-insects and mealy-bugs (Coccidae) also produce honeydew, and are visited by the ants precisely as the aphids are. The manna of the Biblical story, according to Wheeler, “is now known to be the honeydew of one of these insects (Gossyparia mannifera) which lives on the tamarisk. This excretion is still called man by the Arabs who use it as food.” Forel, Cockerell and Wheeler have seen ants tending great herds of coccids, and a few of these insects are found in many nests.

Several kinds of tree-hoppers bear a similar relation to ants. Bare, who studied these matters in Argentina, “watched the larvae of various species of Centrotus being assiduously attended by ants. The larvae are gregarious, frequenting the succulent shoots of plants, and have an extensile organ at the extremity of the body, from which the coveted fluid is emitted.” Wheeler observed whole colonies of ants herding leaf-hoppers in Colorado, and reports that these novel milk-cows “responded to the antennal caresses of the ants in precisely the same manner as the plant-lice and scale-insects.” Some ants confine their tree-hoppers in sheds and shelters similar to those used for the aphids.

The relationship of ants to certain small caterpillars (the larvae of some of the Lycaenid butterflies) has been known for a long time. These little caterpillars, when caressed on the posterior end by the antennae of the ants, give up a drop of sweet liquid, doubtless very similar to that produced by the aphids and coccids.

These larvae are often found in the ants’ nests, and some of the newly emerged butterflies have been seen to come out of the ant-hills. It is said that the ants protect the caterpillars from the attacks of hymenopterous parasites, and De Niceville is authority for the statement that the butterfly will not lay her eggs when there are no ants about: “If the right plant has no ants, or the ants on that plant are not the right species, the butterfly will lay no eggs on that plant. Some larvae will certainly not live without the ants, and many larvae are extremely uncomfortable when brought up away from their hosts or masters.”

Besides the ants’ relationship with the insects which produce sweet substances, there are symbiotic relations of a very different type with a group of insects known as myrmecophiles—ant-guests. These insects, at one stage or another, live in the ant-hills. At least fifteen hundred species of ant-guests are known, and Escherich estimates that there must be at least three thousand altogether. Wheeler thinks that even this estimate is probably too low. At least a thousand of the known species are beetles, and most of the rest are insects of one kind or another, but there are about sixty arachnids and a few crustaceans.

Some of the myrmecophiles are not friends of ants as the name implies, but mere interlopers—scavengers, robbers and assassins. There are a number of small beetles which live in the less frequented galleries of the nest, eat dead ants and brood, kill ailing or crippled ants, and even attack healthy adults when they catch them alone or at some disadvantage. Some of these beetles resemble ants in general appearance, a mimicry which is doubtless of considerable value to them. The ants kill these pests whenever they can, but many are protected by their ability to emit an evil-smelling substance which puts the ants to flight. Others will be killed at once if confined in a small chamber with a few ants, but in a large nest are able to escape by reason of their agility.

Another class of myrmecophiles, known as synoeketes, or tolerated guests, live in the ant-hills without attracting any great attention, being treated with contemptuous indifference by their hosts. The larvae of certain moths and flies, a large number of beetles, and numerous other insects are of this class, and feed largely upon the refuse of the kitchen-middens. Wasmann has studied a group of beetles which live with the nomadic Doryline ants. These camp-followers mimic the legionaries, and march along in their columns apparently unnoticed, being allowed to share the prey taken by the blind warriors. Other beetles live in the nests of the sanguinea, and feed largely upon the tiny parasites from the bodies of their hosts. Certain minute wingless crickets are very abundant in many nests; they are seen to lick the bodies of the ants, and it is supposed that they live upon some cutaneous secretion.

The insect called Attaphila is a sort of miniature cockroach, which lives with the fungus growing Attii, and is, according to Wheeler, the only insect known to be on intimate terms with these ants. A peculiar thing about the Attaphila is that the last joint of the antennae is nearly always bitten off. This insect was formerly supposed to feed on fungus, but has since been found to lick the surface secretions from the ants’ bodies. A little beetle called Oxysoma oberthueri is very like Attaphila in its habits, “mounting the bodies of its host and licking or shampooing them with great eagerness.”

Very different from the furtive, barely tolerated myrmecophiles described above are the three or four hundred species known as true guests, which, to quote Wheeler again, “are no longer content to be treated with animosity or indifference, but have acquired more intimate and even friendly relations with the ants. These true guests are not, therefore, to be found skulking in the unfrequented galleries of the nest, or suspiciously dodging about among the ants, but live in their very midst with an air of calm assurance, if not of proprietorship.” Among these are many beetles bearing tufts of hair which produce some aromatic secretion very pleasing to the ants. The ants rush to lick the odorous tufts, are caressed by the peculiar antennae of the beetle, and feed the latter with regurgitated food. Many of these beetles are cleaned and shampooed by the ants, are often carried about, and favored in other ways, despite the fact that they sometimes devour the ant brood. Some of the smaller species are totally blind, and are permitted to ride about on the ants’ backs for hours at a time.

Another sort of guest is the little mite called Antennophorus, which Janet has found in the nests of several European ants. These mites attach themselves firmly to the body of their host, and it is interesting to note that no matter how many are present on a single ant, they are always so placed that the weight is properly distributed, and the host’s progress not interfered with. These creatures remind one of the ticks found on higher animals like dogs, but they are not parasites in the sense that ticks are—they do not suck the ant’s blood, but reach out and snatch their nutriment from the drops of regurgitated food as they pass from one ant to another.

The ants do not bother Antennophorus much, but there is another mite called Cillibano which is a true blood-sucker, and which they seize and tear to pieces whenever they can. A little blue fly (Orasema viridis) is common in the nests of several Texan and Mexican ants; its larvae attach themselves to the ant larvae and live as parasites. Both the larvae and the adult, however, are fed and fondled by the ants.

Besides these external parasites there are many grubs and worms which live inside the body of the ant, and are comparable to the pin-worms and tapeworms which dwell in the human intestine. These creatures have not been studied extensively, however, and very little is known of their habits and metamorphosis.