W. M. Wheeler and J. W. Champman.
The Mating of Diacamma.
Psyche 29(5-6):203-211, 1922.

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THE MATING OF DIACAMMA'
BT W. M. WH~~~BI~SB AND J. W. CHAPMAN.
Diacynma is a very clearrly defined genus of Ponerine ants confined to India, Ceylon, Southern China, the Malay Archi- pelago, ~ e w Guinea and the northeast corner of Australia. The species were carefully monographed by Emery in 1897, and a list of those known "i 11911 was published by the same .
author in the "Genera Insectomni". There are only thirteen. species, but one of them, the ~ndomalayan rugosum has some 25 ~ubspeciea and varieties, .All the species have large black or bronzy,. more rarely beautifully metallic blue or green, workers {Fig. 11, and pale yellow or yellowish red males (Fig.21, with very long antennse and the pygidium terminating in a c-ed spine. lCoagbu+ from the Entomological laboratory of the Bt~fify h+Itution, HmwMd University, No. 212.
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Pig. 2. Male of Dtam~~na aushlt x5.
The workera are very agile and graceful in their movements and both Rothney (1889) and Bingham (1903). regard them as by far the most intelligent of Oriental ants:
The species of Diacamma are also of imu~ual interest-from . the fact that although several of them are common and have often been observed in the field, no one has ever been able to . find in any one of them a form corresponding to the winged, fertile female, or queen of other ants. Frederick Smith (1863); nearly 60 years ago, described worker and "female" of D. mgosum subsp. tortuo'tornrn and remarked that "the sexea were identified by Mr. Wallace", butthere can be little doubt that he had before him a female belonging to some very different Ponerine genus* poeaibly Bothroponera. In 1899 Col. Bingham remarked that "Diacamma p baa been for years a desideratum of Myrmeco-', logists", and he adds: "It makes me feel aad to think of the many nkst8 I have mhfcd, the hours of bard labeur I have spent, and the language I have used inthe futile search for 9 Diacamma". He then describes two specimens which he found escaping from



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19221 The Mating of Diacamma 205
a nest of D. rugosum subsp. vagans var. indicum and took to be queens, but in 1903 he was compelled to admit that what he had seen was "only a large male." The perusal of his description, however, shows that he could not have seen even males of Diacamma, for they were colored like the worker and sculptured, whereas the male of vagans, of which we have numerous speci- mens, is smooth and yellow. There can be no doubt that he sa-w males of a very different Ponerine ant, namely Odontoponera tra,nsversa Smith, and that he must have been mistaken in regard to their belonging with the vagans workers among which he found them.
These failures led Emery (191 1, p. 64 nota) to conclude that "we must suppose that the female Diacamma resembles the worker so closely as to be confused with it." In 1914 the senior author studied D. australe at Cairns and Kuranda in Northern Queensland and, after alluding to the failure of previous ob- servers to find the missing phase, made the following statement (1915b, p. 335): "In excavating the nests of australe, therefore, I scrutinized the ants very closely in the hope of finding the unknown female, but in vain. Though I searched dozens of nests, I saw nothing resembling a winged female or even a worker with conspicuously enlarged gaster. I found plenty of larvae and pupae and in some of the nests during late October a number of males. These are bright reddish yellow, with con- spicuously long antennae and quite unlike the bronzy black workers. As I failed to find any differentiated queen and as all the pup= were of the same size, I feel confident that in Diacamma the egg-laying function must be usurped by one or more fertile workers during the breeding season."
That the assumptions of Emery and the senior author were well founded has now been demonstrated by the junior author's observations on D. ruqosum subsp. geometricurn Smith in the Phillippines. During a sojourn of six years at Dumaguete in Negros Oriental he found D. geometricum to be a common ant from sea-level to about 3000 ft., living in open "cogon" or shrubby places along the edges of forests, where the vegetation is only three or four meters high. Here it nests under the bark of



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dly and the males tend to fly out of the neet as soon as it ia e accompanying photograph and drawing (Figs; 3 & 4). The ci that the wings of the male had been gnawed away at their Fig. 3. ~erthe worker and ma
left aide xS.
Ie of Diacamma r~gosnm gco~iffricnm in cop&, from th nearly ail tne aevte mtam ft number of small cpUailrical vegetable bodies, wh to be the points of .the flower panicle of a peculiargrass (RnltbA-Ilia . .Th , each of which contains a seed, are scattered by the plant, collected anta and stored in thw neete.
It would mm, therefore, that D. geom@rwum is t e extent vegetarian,




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The Mating of Diacamma
Fig. 4.
Gasters of worker and male Diacamma rugosum geometricztm from the right side x7. bases suggests that the workers may thus prevent the escape of members of the opposite sex from the nest. The same mu- tilation is also practised on the males of Eciton, as noticed by W. Muller (1886) and the senior author (1921, p. 312). And
since the other males taken in the same Diacamma nest were not dealated, it would seem that the workers do not mate with the males of their own colony, that is with their sons or brothers (adelphogamy), but with males that have come from other colonies. The very long sensitive antennae of these insects, so like those of the Ichneumons, may enable them the more easily to seek out alien colonies of their own species. The small size of the Diacamma colony, moreover, indicates that only a single worker is fecundated and assumes the role of a queen, for if several or all of the workers laid fert'ilized eggs the colonies should be much more populous.
Externally the worker found in copula differs neither in size nor in structure from any of her sisters. Examination of the materials in the senior author's collection shows that both in rugosum and its varieties and in the various other species of the genus all the workers taken from the same colony are singu- larly uniform in size and structure, even to the minute details of sculpture and pilosity. As will be seen from Fig. 4, which shows the rasters of the mating individuals from t1he right side, the male and female genital orifices are in broad and very intimate contact. The powerful sting of the female is extruded and is held down by the finger-shaped process of the right external genital valve of the male.




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208 Psyche [October-December
Dissection of a number of Diacamma workers and especially of the mating worker supports the inference that only one indi- vidual in a colony assumes the reproductive function at a time. Unfortunately the material had been in rather weak alcohol for several months and the very hard chitinous integument of the gaster had prevented penetration, so that the internal organs were considerably decomposed. In many of the workers, of which more than 20, belonging to three colonies, were dissected, no ovaries could be detected. In one, however, two ovarioles were clearly seen, each of the type figured by Miss Holliday (1903, Fig.Ab, p. 295) for the ergatoid queen of Lobopelta elongata,i.e. with a large number of very small ova separated by clusters of nurse-cells. .Such undeveloped ovaries were probably present in all the speci- mens but could not be detected on account of defective preser- vation. This may alsoexplain our inability to find a sperma- theca in any of these individuals. Fortunately the mating worker was in a somewhat. better state of preservation. The ovaries were found very far forward, in the large first gastric segment and applied to the sides of the crop. There were five ovarioles in each ovary and the lowermost egg in each ovariole was fully developed and of an elongate-oblong shape, as in some other Ponerinse (Pachycondyla, Lobopelta). The vagina and a large spermatheca attached to its dorsal wall were filled almost to bursting with compact masses of spermatozoa. For some time evidence has been accumulating to show that Diacamma is not the only ant genus in which the winged queen has been lost and her function in the colony usurped by a fertile worker. The senior author, in the paper above mentioned(1915b, p. 337), called attention to the fact that winged females do not exist in the Ponerine genus Rhytidoponera, which is represented by a number of species in the Australian and Papuan Regions. The same condition very probably obtains also in the South African Streblognathus and Ophthalmopone and in the Neotro- pica1 Dinoponera, all genera belonging to the same subtribe as Diacamma (Pachycondylini). He also stated in his monograph of the Australian honey-ants of the Dolichoderine genus Lepto- myrmex (1915a,p. 260) that true queens are inall probability absent



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19221 The Mating of Diacamma 209
in this genus and "that there are in each colony one or more fertile workers which supply the eggs that delevop into workers and males.'' And Arnold (1916, p. 195) says of a species of the South African genus Ocymyrmex, which belongs to the subfamily Myrmicinse: "1 have frequently dug up the nests of the variety arnoldi [of 0. weifzaeckeri Emery] without ever having found a female of any sort, nor have females of any species been des- cribed up to now. I believe that the genus will be found to have only ergatoid queens, or that the egg-laying function (with the production of males and females) is possessed by the whole worker caste."
The fertile workers of Diacamma which function as queens are obviously not to be confused with two other types of wingless females, the ergatoid, or ergatomorphic queens and the dichtha- diigynes. Ergatoid queens are of rat,her frequent occurrence, either as the only form of fertile female or coexisting in the same species with winged queens, in one genus of Pseudomyrminse (Viticicola), in at least one genus of Formicinse (Polyergus), in several Myrmicine genera (Monomorium, Myrmecina, Lepto-' thorax, Crematogaster, Harpagoxenus, et c.) and especially among the Ponerinse (Eusphinctus, Cerapachys, Acanthostichus, Acan- thoponera, Paranomopone, Alfaria, Megaponera, Ponera?Ony- chomyrmex, Leptogenys, Anochetus and Champsomyrmex) . In some cases (Leptogenys, Paranomopone, Megaponera and Eusphinctus) the queens differ very little from the workers, ex- cept in having traces of ocelli, a somewhat thinner petiole or a larger abdomen; in others the thorax is more complicated in structure and approaches that of the winged queen, while in still others (Acanthostichus, Onychomyrmex, Nothosphinctus) there is an approach to the dichthadiigyne, which is the only queen in all the genera of Dorylinse, a characteristic form with very simple thorax, without eyes or with minute vestiges of eyes and ocelli and with a huge abdomen. Most of the ergatoid forms may be derived from the typical winged queen through a loss of the wings and a progressive, degenerative simplification of other characters, lA fourth form of female, the pseunogyne, is not discussed because it is pathological and does not function as a reproductive caste.



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210 Psyche [OC tober-~ecember
but it is conceivable that the dichthadiigynes may have arisen from fertile workers like those of Diacamma after complete phylogenetic suppression of the winged queen. The latter sup- position will have to be tested by thorough morphological study of all the available fertile female forms. The conditions in Diacamma are suggestive also from an- other point of view. It has long been known that well-fed worker ants may lay eggs, but no one has ever seen a male copulating with aworker, and only Rcichenbach, Mrs. Cornstock and Crawley have found that eggs laid by workers may develop into workers. All other authors (Miss Fielde, Janet, etc.) maintain that such eggs invariably produce males. In Diacamma geometricurn we actually have an ant whose workers copulate with t'he males and must therefore produce worker as well as male offspring, since there is no morphologically differentiated queen. Further studies
of tropical ants in the field will probably compel us to to abandon certain other generalizations which we have reached from a too exclusive study of temperate European and North American species confined in artificial nests.
BIBLIOGRAPHY.
1916. Arnold, G. A Monograph of the Formicidse of South Africa (Myrmicinse). Ann. South Afric. Mus. 14, 1916, pp. 159-270, 3 pis.
1899.
Bingham, C. T.
Note on Diacamma, a Ponerine Genus of
Ants, and of the finding of a female of D. vaqans Smith. Journ. Bombay Nat. Hist. Soc. 12, 1899, pp. 756, 757. 1903. -------- The Fauna of British India including Ceylon and Burma. Hymenoptera, Vol. 2. London, Taylor & Francis, 1903.
1897. Emery, C. Revisione del Genere Diacamma Mayr. Rend. Sess. R. Accad. Sc. 1st. Bologna, 1897. pp. 147-167, 1 pi.
1911 -------- Genera Intsectorum. Family Formicidse, Subfamily Ponerinse. Fasc. ll8,lg 11, pp. 1-125, 3 pis.
1903. Holliday, M. A study of Some Ergatogynic Ants. 2001. Jahrb. Abth. Syst. 19,1903, pp. 293-328, 16 figs-



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19221 The Mating of Diacarnrna 211
1886. Muller, W. Beobachtungen an Wanderameisen(Eciton hamatum).
Kosmos 1, 1886, pp. 81-93, 1 fig.
1889. Rothney, G. A. J. Notes on Indian Ants. Trans, Ent. Soc. London, 1889, pp. 347-374.
1863. Smith, F. Catalogue of the Hymen~pt~erous Insects collected by Mr. A. R. Wallace in the Islands of Mysol, Ceram, Waigiou, Bouru and Timor. Journ. Proc. Linn. Soc. London. Zool. 7, 1863, pp. 6-48. 1915a. Wheeler, W. M. The Australian Honey-ant,s of the Genus Leptomyrmex Mayr.
Proc. Amer. Acad. Arts
Sc. 51, 1915, pp. 255-286, 12 figs.
1915b. -------- On the Presence and Absence of Cocoons Among Ants, the Nest-spinning Habits of the Larvae and the Significance of the Black Cocoons among Certain Australian Species. Ann. Ent. Soc. Amer. 8,1915, pp. 323-342, 5 figs.
1915~. -------- Paranomopone, a New Genus of Ponerine Ants from Queensland. Psyche, 22,1915, pp. 117-120, 1 pi.
1916. The Australian Ants of the Genus
Onychomyrmex.
Bull. Mus. Comp. 2001. 9, 1916,
pp. 45-54, 2 pis.
1918.
The Australian Ants of the Ponerine
Tribe Cerapachyini. Proc. Amer. Acad. Arts Sc. 53, 1918, pp. 215-265, 17 figs.
1921. ------- Observations on Army Ants in British Guiana. Proc. Amer. Acad. Arts Sc. 56, 1921, pp. 291-328, 10 figs.




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