Pachysima latifrons, Emery

Wheeler, W. M., 1922, The ants collected by the American Museum Congo Expedition., Bulletin of the American Museum of Natural History 45, pp. 39-269 : 120-124

Pachysima latifrons (.Emery)

Text Figures 28, 29, 30, and 31

Worker.-Length 7 to 8.5 mm. Similar to the worker of P. aethiops but smaller, smoother and more shining, and much more finely punctate, with the frontal carinae somewhat farther apart and more nearly parallel. The mandibles have less oblique apical borders and are smooth and shining and sparsely punctate, not coarsely striated as in aethiops ; the mesonotum is shorter and semicircular; the epinotum in profile somewhat lower and more rounded; the petiole bears on its ventral surface a single large acute, backwardly directed spine, instead of two spines, and the postpetiole has in the same relative position a smaller spine of similar shape, representing the larger, blunter projection of aethiops . The erect hairs and pubescence on the body are distinctly more abundant in latifrons , and the clypeus has a conspicuous fringe of yellow ciliary bristles, which are not developed in aethiops , and the antennal scapes have a row of long scattered hairs on their anterior surfaces. There is no difference in coloration.

Female.-Length nearly 12 mm. Closely resembling the worker and differing by the same characters from the female of aethiops . The head and thorax are more slender than in the latter species and the petiolar and postpetiolar nodes are narrower and less submarginate on the sides. The pilosity and pubescence are much less developed on the body than in the worker, though the clypeus has conspicuous yellow ciliary bristles and the antennal scapes have a few long hairs along their anterior surfaces. The wings are blackened like those of aethiops .

Described from numerous workers and a single female taken from a colony at Niangara (Lang and Chapin), also in hollow twigs of a Barteria, presumably B. fistulosa. This species appears to be confined to western Africa; its distribution is still imperfectly known.

The larval stages are quite as remarkable as those of P. aethiops and exhibit four stages as follows.

The trophidium, or first stage larva, shown in Fig. 29a-b, is very hypocephalie, the prothoracic segment being greatly enlarged and projecting anteriorly. Stained preparations in toto and sections show that the portion of the fat-body in this segment is heavily charged with urate crystals, so that it undoubtedly functions as a storage kidney till the Malpighian vessels are sufficiently developed to excrete. The first and second pairs of prothoracic appendages of the xthiops larva are absent, but the third pair is very large and embraces the sides of the head. The meso- and metathoracic segments each bear a pair of slender, pointed appendages, the first abdominal segment a huge leg-like pair which are swollen and fusiform at the base and running out into a slender process which forms an obtuse angle with the basal portion. The sternal region between these appendages is protuberant and its cuticular covering, like that of the four pairs of appendages, is minutely prickly, unlike the smooth cuticle of the remainder of the body. Sections show that both the four pairs of appendages and the sternal swelling are exudate organs, though the prothoracic and abdominal pairs are evidently much more important than the others. The prothoracic appendages are filled with blood and very little fat-tissue, but their hypodermis is much thickened and consists of crowded cells arranged in peculiar clusters. In section, the abdominal appendages appear as in Fig. 30. The fusiform base is filled with large, clear trophocytes, or fat-cells, some of which in the middle of the swelling may be filled with urate crystals, like those in the prothoracic storage kidney, but the slender, tubular distal portion contains a granular liquid which can only be regarded as an exudate derived from the trophocytes in the basal enlargement. This exudate is evidently filtered through the thin cuticle covering the appendage by pressure, for there is a rather elaborate system of muscles, as in the aethiops larva, surrounding the bases of the appendages and capable of subjecting then contents to pressure. The head is small and has soft, blunt, rudimentary and unchitinized mandibles and the labium bears a pair of long,palp-like appendages, which project forward in the deep depression between the head and the swollen sternal portion of the first abdominal segment. These are probably also exudatoria and seem roughly to correspond to the unpaired tentacle of the aethiops larva. The structure of the mouth-parts shows that the larva in this stage is fed with liquid food regurgitated by the workers. The convex dorsal surface is beset with sparse, curved bristles of uniform thickness, with blunt tips. The segmentation of the body is indistinct and its posterior end curves forward and terminates in a large tubercle with the anal orifice just anterior to its base. The Malpighian vessels have only just begun to develop at the blind end of the proctenteron where it abuts on the posterior end of the large, elliptical mesenteron, or stomach, but no salivaiy glands can be detected.

In the second stage larva (Fig. 31 a) the body is more elongate and cylindrical and the four pairs of appendages can still be recognized though considerably smaller in proportion to the remainder of the body. The mandibles arc becoming chitinized. Many of the long hairs on the dorsal surface are still present, but a general covering of short, sparse hairs has made its appearance.

The third stage larva (Fig. 31 b) is larger and still more elongate and cylindrical and shows a further regressive development of the exudatoria. Those on the meso- and metathoracic segments have disappeared and the abdominal pair has short broad bases with the distal portions attenuated to slender points. The labial appendages have also disappeared. The mandibles are well developed and chitinized, and the larva is now fed with pellets of crashed insects, like the aethiops larva in the corresponding stage. These pellets were found still in situ in several of the alcoholic specimens as represented in the figure (Fig. 31b). The pellet lies in the deep pocket between the head and the sternal protuberance of the first abdominal segment and is, therefore, within easy reach of the mandibles and labium of the larva. Cleared preparations show that the salivary glands have made their appearance, though they are small and slender.

The anterior end of a fourth stage or adult larva is shown in Fig. 31c. The exudatoria of the prothoracic segment now appear merely as a pair of welts or folds embracing the sides of the head and continuous with the more dorsal portions of their segment, which is relatively smaller and less projecting than in the preceding stages. The appendages of the first abdominal segment are still distinct but their distal portions are reduced to mere points, sometimes absent in larvae just before pupation, and the sternal swelling is much less prominent. In this stage the larva resembles that of Tetraponera throughout its various stages. In the third and fourth stages of the latifrons larva, as in the corresponding stages of xthiops, the salivary glands probably furnish secretions which are useful both in the extra-intestinal digestion of the food-pellet and as exudates that can be imbibed by the workers.