Megaponera foetens (Fabricius), Mayr

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 : 64-69

Megaponera foetens (Fabricius)

Plate VI, Figure 2

Zambi, [[worker]]; Niangara, [[worker]], [[queen]]; Rungu, [[worker]]; Avakubi, [[worker]]; Faradje, [[worker]]; Panga to Banalia, [[male]]; Boyulu, [[worker]]; Niapu, [[worker]]; Garamba, [[worker]]; Akenge, [[worker]]; Gamangui, [[worker]] (Langand Chapin); Malela, [[worker]] (J. Bequaert).

Seventeen of the specimens from Boyulu, Niapu, Garamba, Akenge, and Gamangui were taken from the stomachs of four species of toads (Bufo funereus, superciliaris, regularis, and polycercus) and a male from Faradje was taken from the stomach of a frog (Rana occipitalis).

The smaller individuals have the vertex and pronotum very shining, the mandibles toothless, and the funicular joints of the antenna; much shorter and more transverse than in the larger workers (Fig. la and b) and were therefore formerly regarded as a distinct species ( M. crassicornis Gerstaecker ). A worker media was also described by Emeiy as a distinct species, M., dohrni. At one time he interpreted the smaller individuals as the true workers and the larger as ergatomorphic females. Arnold, who found this view improbable for the reason that the large are about four times as numerous as the small individuals in the colony, has recently discovered the true female.1 It is of the ergatomorphic type, with a slender wingless thorax like the large worker and measures 18.5 mm. The petiole, however, is squamiform and not cuboidal as in the worker and the gaster is much more voluminous. It therefore resembles the females of Leptogenys (subgen. Lobopelta ) and Onychomyrmex which I have described in former papers.

Armies of Megaponera were frequently observed by Mr. Lang preying on termites or carrying the larvae and pupae in files, sometimes of 300 or more individuals. In the literature there are some interesting accounts of the habits of this ant.2 Wellman observed it in Benguela and informed Forel of its habit of marching in populous columns.3 In a later paper4 Forel published some observations of Prell on the same ant in German East Africa. He found it running in single file on the road. Most of the larger individuals were carrying worker and soldier termites in their jaws and Prell was struck both by the sonorous stridulation of the army and by its strong odor, which resembled that of oil of bitter almonds and was imparted to the alcohol of the vial in which the specimens were preserved. Similar observations were made by Bequaert in the Katanga.5

A more detailed, though incomplete, account of a raid on termites is given by Alluaud and Jeannel in Santschi's paper on the ants they collected in East Africa:

When they are disturbed and run away the Megaponera foetens stridulate , and the noise made by a troop of them can be heard at a distance of several meters. We noticed this on several occasions, particularly at Fort Hall and New Moschi. At the latter station on the morning of April 10, 1912, in a corner of the forest at the edge of the Rau River, we encountered a troop of several hundred Megaponera marching in a column several abreast, apparently moving with decision to a predetermined goal. They descended the bank of the stream, stridulating loudly. We were unfortunately busily occupied at this spot collecting a lot of large Papilio which came down to the river to drink, so that we did not think of following the Megaponera army. An hour later these ants returned in good order in the reverse direction, each of them carrying in its mandibles a whitish pellet consisting of dead termites glued together with saliva. Some of them carried as many as ten to twelve termite workers thus agglutinated, others only two or three soldiers; one carried a dealated male, possibly the king of the plundered termitarium. The number of termites in a pellet varied with its size, but not an ant returned without something. While collecting a number of these Megaponera fcetens with their booty we experienced the effect of their sting, which is lancinating and very painful but very transitory.

In his monograph of the Formicidae of South Africa (loco citato, p. 47) Arnold says:

It is a common ant in Rhodesia and lives almost exclusively on termites, which are carried off by means of carefully arranged raids in which the ants march in double file. This is the species which is popularly called the "Matabele" ant, and like its cousin Paltothyreus , it is also endowed with a very offensive odor. They stridulate very loudly when disturbed, and their sting is exceedingly painful. The entrance to the nest consists of one or more simple holes without any mounds of earth around them.

In the Proceedings of the Rhodesian Scientific Association, XIII, 1914, p. 26 et seq., Arnold has recently published a fascinating description of the extraordinary way in which the Matabele ant changes its nesting site and is followed by its numerous guests. I quote the greater part of his account, as the journal in which it appeared may not be accessible to my readers:

This is eminently a termitophagous species, and it is likely that it changes the site of its nest more often than is the case with the majority of our ants. When we bear in mind how continuous their assaults are on the colonies of termites, it seems very probable that the supply of the latter insects may be so diminished within the practical range of the camp of the raiders that the latter may find it advantageous to move their quarters from time to time to new and more fruitful country. The migration of this ant which I am about to describe is of particular interest, apart from the behavior of the guest insects, because it was the occasion of the discovery of the true queen of the species. * * *

My attention was attracted to this migration by seeing a mass of these ants assembled together with their larvae and pupae, in the open. On one side, many workers were to be seen bringing along the larvae in their jaws, on the other side of this mass a few workers were moving in the other direction, in a somewhat hesitating manner. Following the track backwards, I came to the site of the old nest, situated about 15 feet away. Returning to the camp, it was seen that some workers had started to pick up the larvae again, and were carrying them yet further away from the original nest, only to be laid down again at about another 15 feet further away. Subsequent observations showed that the migration was carried out in three stages, three temporary camps being formed between the old and the new nests, which were about 60 feet apart. The method adopted by the insects was as follows. First of all, the eggs, larvae, pupae and males were taken from the old nest and put down at the first camp, from which many workers were to be seen hurrying back to fetch away the rest of their charges. In the meantime, a few workers were to be seen pacing up and down on the other side of the camp. They did not carry any larvae and it would almost seem as though they had some idea of the numerical composition of the colony, and of what the volume of the first camp should be, before the old nest could be considered to have been emptied by its inhabitants, and the proper moment to have arrived for another start to be made. However, after about six or seven minutes, the march recommenced; and within a short time the second camp had been made at a distance of about 15 feet from the first. Similarly a third and last camp was formed further on. It was while the first camp was about to break up that I saw an insect then much larger than the largest worker, and which, when captured in the third camp, proved, to my surprise, to be the queen.

The entrance to the old nest was a hole about 1 inch across, which ran down vertically for about 5 inches and then branched off at an angle. Looking down this hole, the various guests and parasites could be seen climbing up the walls in an almost continuous stream, hastening to join their hosts in their new home. These insects comprised a Lepisma, two species of staphylinid beetles, a histerid beetle and an onthophagous beetle; there was also a spider. The Lepismas as usual were very plentiful; of the larger staphylinid I saw only one specimen, but of the smaller sort and of the other beetles very many examples occurred, and during the half hour or so through which I watched the procession, about two dozen specimens of the spider were counted. Had it been possible to have cinematographed the scene, it would have furnished us with a film of surpassing interest. Here, as in the case of Myrmicaria , the myrmecophiles were able to follow the tracks of their hosts without any delay or uncertainty. Occasionally one of the smaller staphylinids would leave the beaten track for a short distance and then return to it again a little further on, but to the majority of these commensals, the odour of their hosts had laid down a path as clearly marked as a macadamized road would be to our eyes, so that with the above exception, it was rare to see any of these insects swerve from the line of march by as much as an inch.

This motley crew of cringers, thieves, murderers and body-snatchers did not appear to attract the slightest attention from their victims the ants, which were too busy with the work in hand to waste any time on the rabble following in their wake. Of all this crowd, the spiders alone were able to keep pace all the time with the ants, but the slowest, the very small histerid, even at its most feverish pace, did not succeed in covering more than 2 inches per minute, so that it would have arrived at the new nest about six hours after leaving the old. Those beetles which managed to reach the different camps, while these were still intact, buried themselves in the heap of larvae and cocoons, where they remained until the gradual depletion of the mass made it clear that they had not arrived at the site of the real nest and that another wearisome journey had to be made to attain their goal.

The spiders moved about in the camps in a very easy and unconcerned manner, making no attempts to hide under the piles of cocoons. They ran over the backs of the ants, mingling in a friendly way with the crowd; yet even in the hurry and bustle of this march, it was not possible for these animals to conceal entirely their method of earning a living. A worker ant, carrying a larva in its jaws, was seen just about to pass a spider standing on the edge of the camp. The spider ran up to the worker, stroked it with its front pair of legs for a second or two, and then plunged its fangs into the larva. The latter was released by the ant after a little hesitation, and within five minutes had been sucked dry by the spider. We know that there are many ant parasites which live chiefly on the young of their hosts; but usually these insects offer, on various parts of their bodies, those bribes in the shape of trichomes which make the ants careless of, or oblivious to the true nature of their guests. On the other hand, there are the synceketes, or indifferently tolerated guests, with which perhaps the histerid and onthophagous beetles found on this occasion should be classed, which do not usually bear trichomes. They owe their immunity from attack on the part of the ants, either to their insignificant size, or to their awkward shape, which prevents the ants from seizing hold of them. But it is difficult to understand how the spiders can live unmolested in the nests of such a powerful and vicious ant as Megaponera foetens and be allowed to feed on the larva;, without apparently the mildest protest. They do not possess trichomes, nor are they so constructed, by smoothness or hardness of texture, as to prevent the ants from seizing hold of them.

The staphylinids arc probably to be placed in the category of synechthrans, or inimically persecuted intruders, which includes a number of insects which skulk about ants' nests, and get a living by rummaging about in the refuse heaps or kitchenmiddens, or by attacking solitary workers in the lonely corners and by-ways of the settlement. * * *

In conclusion, it should be pointed out that in these latitudes, migrations of ants can be expected to take place only after sunset, or if earlier, only on dull and cloudy days, as was the case with Megaponera , since the delicate larvae cannot bear a lengthy exposure to the rays of the sun.

Two of the viah of Megaponera collected by Mr. Lang contained a number of cocoons and larvae in various stages, so that, on reading Arnold's account, it seemed probable that the brood might show adaptations to being carried about and exposed to the sunlight. A study of the material shows that such adaptations can be detected. The larvae (Fig. 8a and b) arc grayish white, long and subcylindrical, and only slightly curved, with strongly marked segments and with smooth, remarkably tough integument, which is quite hairless in all stages, a condition I have never observed in any other ant larva. The head is very large, rounded, strongly chitinized, and terminal, with long, acute, falcate, edentate mandibles, minute vestiges of antennae, and very prominent tactile sensillae on the maxillae and labium. The size of the head and mandibles shows that the larvae are fed on pieces of termites and not with regurgitated liquid food, and the strong integument is evidently an adaptation to exposure to the air and light and to the exigencies of frequent and protracted transportation in the powerful denticulate jaws of the workers. The nudity of the integument indicates that even the very young larvae are carried singly and not in bunches held together by interlocking hairs as in most other species of ants. The cocoons are black and remarkably tough, characters which I have observed in certain Australian Ponerinae of the genera Diacamma and Rhytidoponera as adaptations to exposure to sunlight.1 This interpretation is confirmed by Mr. Lang, who, without knowing of my observations, informed me that he was surprised to find Megaponera often exposing its dark cocoons in heaps to the sunlight.

Recently, in a letter to Prof. Poulton,2 G. D. H. Carpenter records some additional observations which he was able to make on M. foetens southwest of Lake Victoria:

I see a good deal of the ant Megaponera foetens here: one is always coming across their long, solemn, slowly marching, black processions -of any number from 50 to 500 or so. I have never seen them carrying any other booty but the species of termite which abounds here -the one I have alluded to before. It lives underground and makes no hills -coming out of little holes and running about, uncovered, in the open, to get bits of live or dead grass which it carries down the holes. Presumably in correlation with its open-air habits, its color is much darker than the large termite whose hills I used to destroy on the islands, and which devoured my house. This one does not attack wooden posts nor does it make covered runs. Curiously enough, I have never seen an}' soldiers, which is perhaps why Megaponera wages such ceaseless war against it. This ant, when it goes out in column, wanders about looking for the termite holes. Immediately one is found there is great excitement. The little bits of grass which sometimes plug the entrance are dragged out, and the ants scramble down the hole very shortly reappearing with termites, feebly struggling in their jaws. Sometimes there seems evidence of an underground barricade, as ants come up to the surface with bits of dead grass, etc., as if they were breaking down hastily erected barricades! One can almost picture the termites hastily throwing up partitions of grass and earth to keep back the invaders. It would be interesting to know if the reason why Megaponera is absent from some parts, is because this particularly defenceless termite is absent also.