Ant colonies > Ant body parts > Ant head

Ant head


Ant headThe ant's head varies enormously in shape. It may be circular, elliptical, rectangular or triangular, and all its parts may show an extraordinary diversity of adaptive characters. It consists of the cranitim proper, which is very much constricted behind at its articulation with the thorax, the eyes, the clypeus, or epistoma, a plate of very variable outline and immovably articulated with and set into the anterior portion of the cranium, the antennae, and the mouth-parts, comprising an unpaired upper lip, or labrum, the mandibles, maxillae and labium, or lower lip. In the last the originally separate and paired embryonic appendages are fused in the median line so that they form a continuous floor for the mouth or buccal cavity.

In the cranium the following regions may be distinguished: the front, a region bounded anteriorly by the posterior edge of the clypeus and laterally by a pair of ridges, the frontal carinae or laminae, just mesial to the insertions of the antennae. A small, usually triangular, median region, the frontal area, can be easily seen in the middle line just back of the clypeus, and often there is an impressed line, the frontal groove, extending back from this area over the middle of the front. The frontal region passes without definite boundary into the vertex and temples, the former extending posteriorly, the latter lying above and behind the eyes. The short region between the vertex and the narrow opening, or foramen through which the alimentary tract and nervous system pass into the thorax, may be called the occiput.

The cheeks, or genae, comprise the portions of the cranium anterior to the eyes and lateral to the frontal carinae. The ventral portion of the head, bounded in front by the labium, on the sides by the cheeks and extending to the occipital foramen, is the throat, or gula. It is well-developed in the ants and is usually divided into two equal halves by a longitudinal suture.

The mandibles, being the parts with which the ant comes into most effective relations with its environment, present, like the beaks of birds and the teeth of mammals, a bewildering variety of structure. They are used for excavating soil or wood, cutting up the food, fighting, carrying the prey, their young or one another, and in some species, even in leaping by closing them rapidly against hard bodies. Ants are remarkable in being able to open and close their mandibles independently of the maxillae and labium. These organs, which lie underneath the small and vestigial labrum and close the mouth completely except when the insect is feeding, have a complicated and interesting structure.

The maxillae are paired and each consists of the following (cardo), the stem (stipes), the maxillary pieces, or sclerites: the hinge palp, which may be from 1-6-jointed, an inner blade (lacinia) and an outer blade, the galea. The galea bears a row of gustatory papillae and a row of bristles which are used in cleaning the legs and antennae. The lacinia is membraneous and toothless and shows that the ant feeds on liquid substances only. This is also proved by the structure of the labium, which consists of the following sclerites: the hind chin (submentum), the chin (mentum) and the tongue (glossa), all unpaired, and the labial palpi, consisting of from one to four joints, the paraglossae and hypopharynx, which are paired.

The tongue, with which the ant rasps off or laps up its liquid or its fellows, is a protrusible, semi-liquid food, and cleans itself elliptical pad, covered with fine trans­verse ridges. At its base lies the opening of the salivary duct. The paraglossae are small sclerites beset with rows -of bristles. The hypopharynx, which is less developed than in some of the other and Hymenoptera, such as the wasps, covers the mentum and paraglossae. Its upper portion is somewhat lobed and bears two rows of backwardly directed bristles, which form a V and seem to be used for holding the food fast in the mouth: The upper lip, or labrum, forms the roof of the mouth. It is poorly developed and consists of a bilobed plate hidden beneath the anterior border of the clypeus.