Myrmicaria eumenoides (Gerstaecker) subspecies opaciventris (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 : 143-145

Myrmicaria eumenoides (Gerstaecker) subspecies opaciventris (Emery)

Plate VIII, Figures 1 and 2

Malela, [[worker]]; Thysville, [[worker]]; Stanleyville, [[queen]], [[male]]; Avakubi, [[worker]], [[queen]]; Medje, [[worker]], [[queen]], [[male]]; Akenge, [[worker]]; Bafwabaka, [[worker]]; Ngayu, [[worker]]; Faradje, [[worker]], [[queen]] (Lang and Chapin); Walikale to Lubutu, [[worker]], [[queen]] (J. Bequaert); Yakuluku, [[queen]] (J. Rodhain). Seventy-five workers and one female from Bafwabaka, Ngayu, Medje, Akenge, and Stanleyville were taken from the stomachs of toads (Bufo regularis, B. funereus, and B. superciliaris); a single worker from Faradje was taken from the stomach of a frog (Rana occipitalis).

Neither Forel nor Santschi seems to me to have recognized this form very explicitly. Several years ago I received from the former six workers labelled "Benguela (Buchner)" and, as Emery's ergatotypes bore the same label and were also received from Forel and as my specimens agree perfectly with Emery's description, I feel confident that they are cotypes. Later I received a worker and three dealated females from Gaboon (Staudinger) and, as Emery mentions specimens from the same locality, I believe that I have before me also the female of the true opaciventris. The workers measure about 5 to 6 mm. and are pale ferruginous brown, with the antennae, legs, and gaster more fuscous. The mandibles have oblique 5-toothed blades; the clypeus is carinate. The epinotal spines are rather slender and very slightly bent downward, the base of the epinotum is less concave than in the typical eumenoides, the peduncle of the petiole is distinctly shorter and not longer than the node. The petiolar and postpetiolar nodes are laterally compressed and of the same height, the ventral surface of the postpetiole, unlike that of eumenoides, is swollen, and projecting and angular in front. The surface of the head and thorax is somewhat less shining than in eumenoides, the rugae on the front, pleurae, pro-, meso- and base of epinotum more sharply and regularly longitudinal and not reticulate. The gaster has the basal half or, in some specimens, the whole surface opaque and densely punctate, whereas it is smooth and shining in typical eumenoides. The nodes of the petiole and postpetiole have shining summits and in some specimens the sides of the petiole are also smooth and shining, in others like those of the postpetiole, finely punctate and even feebly longitudinally rugulose. In the female, which measures 13 mm., the petiole and postpetiole are sharply longitudinally rugose, the summit of the former concentrically rugose, the scutellum vermiculately rugose. Emery's description of the male, which I have not seen, includes no mention of characters that would distinguish it from the male of the typical eumenoides.

Numerous specimens from the various Congo localities cited above seem to me to be referable to Emery's subspecies, though they differ more or less in the sculpture of the petiole, postpetiole, and gaster and in being mostly of a darker color. They average larger than the specimens of variety congolensis and variety crucheti , the workers being 5 to 6.5 mm. The petiole and postpetiole, especially the latter, are nearly always more or less longitudinally rugulose on the sides, though sometimes merely punctate, as Emery remarks in the original description. The specimens from Walikale have the entire gaster opaque and punctate, whereas in others it is punctate usually only on the anterior half of the first segment. This character, however, varies in individuals from the same colony. Santschi says that the gaster of the worker is "entierement sculpte, mat, brun clair," but Emery describes the gaster as fuscescent, with the anterior half of the first segment opaque.

Trägardh and Arnoldi have described the nests of the typical eumenoides of East and South Africa. The latter's account runs as follows.

The colonies of this species are usually very large, often comprising 1000 or more workers. The latter bite and sting fiercely, but the sting is rather blunt, and does not easily pierce the human skin. Although their gait is slow, they are nevertheless active insects, travelling over large areas in search of food, which seems to consist chiefly of other insects. They do not appear to be aphidicolous, nor to attend membracid or lepidopterous larvae for their secretions, yet they are known to harbour in their nests many myrmecophilous insects. A nest examined by me contained the following species of beetles: Allodinarda myrmicariae Brauns; Ogmocerus raffrayanus Brauns and Batrisus myrmecariophilus Brauns. The Botanical Gardens in Durban are infested with this species, but the examination of a large number of nests revealed only one species of myrmecophile, Allodinarda kohli Wasm.; which, however, was plentiful, as many as three dozen being taken in one nest. The nest has numerous entrances, and is surrounded by large heaps of excavated material, often covering an area of several square feet.

Arnold3 has also described and figured the puparium of a fly (possibly a form allied to Microdon?), with a peculiar tray covered with trichomes at the posterior end of the body, as occurring in the nest of M. eumenoides with the myrmecophilous beetles cited in the foregoing quotation. The following is his account of the migration of the colony and its guests to a new nest.

I left this nest without filling up the hole, so that in about a week's time it was filled with rain after a heavy shower. The water must have filtered through the soil and almost saturated the nest, for it took nearly half an hour for all the water to disappear from the hole. This state of affairs had evidently made the nest so uncomfortable that the ants decided to move to new quarters about 9 feet away. They began to do this about seven o'clock that evening, or perhaps a little earlier, for the migration was in full swing when I came on the scene again at that hour. Remembering the reputation which this ant has for harboring guests, and also the observations made by various entomologists on some European ants which, when moving to a new nest, are in the habit of carrying their guests with them, I decided to watch this migration carefully. At first I could see no guests at all; the workers were carrying in their mandibles only their own larvae, pupae or males. In fact I was looking at the workers so attentively that I failed to notice their smaller companions on the road, to which my attention was directed by suddenly catching sight of a Lepismid running by. Going back then to the old nest, I saw at intervals various myrmecophiles crawling out of the pit made by my former excavation, and following the tracks of their hosts, to which they were guided, of course, by the sense of smell. These parasites included three different species of beetles, viz. a staphylinid, and two species of pselaphids, together with the common lepismid found in the nests of nearly all our ants. No time was wasted by any of these insects, for once over the brow of the pit, they continued straight along the narrow path leading to the new quarters. While on the march they were utterly ignored by their hosts, but on arriving at the entrance of the new nest, it was noticed that some of the pselaphids were seized by the ants dawdling around, and taken down into the nest. This change of dwelling took some hours to complete, for at midnight it was still in progress.

Mr. Lang contributes the following note on the habits of the subspecies opaciventris at Avakubi: "These ants, called 'dufluguntu' by the natives, are very common and noticeable because they tend to congregate in great numbers about any piece of meat or a dead insect. On one occasion I saw them tear up and carry off a butterfly two inches in diameter in exactly two minutes and a half. They are harmless and therefore not feared by the natives. A young Manis, which I kept in captivity, enjoyed making a meal of them. The nests, as a rule built at the bases of trees or bushes, can be easily recognized by the mound of loose earth thrown up while the chambers are being excavated. The walls of the chambers are not hardened or smoothed as in the nests of some other ants. One nest which I examined extended seventeen inches below the surface. It had many ramifications, though most of the brood was found around the roots of the tree. The whole nest, when exposed, covered an area less than two feet in diameter. These ants build long tunnels open above or with small openings (one-eighth inch), surrounded by a heap of loose particles. One of these, more than an inch wide, crossed a certain road in several places. I have seen a number of these tunnels superimposed one above another so that I could drop a stick down thirteen inches. In these tunnels the ants travel back and forth in great numbers."