Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Mandibles with about 8 teeth, in graded series from large apical tooth to smallest teeth basally; mandibles coarsely striate, opaque; occipital carina not visible in face view; propodeal suture moderately impressed; dorsal and posterior faces of propodeum distinct; propodeum with longitudinal median depression; petiole with broad, well-developed anteroventral keel; postpetiole with sharp anteroventral tooth; color orange; body in general densely hairy, covered with dense, somewhat bristly yellow setae; HW 0.80; HL 0.90, SL 0.82; WL 1.30 (n=1).
This does not exactly match some details of Wheeler's description. The type locality of symmetochus is B.C.I. in Panama.
Bolivia, Brazil, Panama, Costa Rica. Costa Rica: Atlantic lowlands.
This species appears to be a specialized associate of small Attini (Wheeler 1925, Brandao 1990, Adams et al. 2000), a habit possibly shared with other species of Megalomyrmex such as wettereri, mondabora, and silvestrii. Wheeler (1925) found numerous colonies nesting with Sericomyrmex amabilis on Barro Colorado Island, Panama. He observed a number of colonies in the lab, and made the following observations:
The colonies of the Cepobroticus [Megalomyrmex symmetochus] so frequently found living with Sericomyrmex amabilis were decidedly less populous than those of their host. The largest comprised less than 75 individuals, and often the number did not exceed 40 or 50. In every nest a dealated mother queen was present. She usually took up her station, surrounded by a group of her workers, in one of the crypts of the fungus garden a short distance - half to three quarters of an inch - from the Sericomyrmex queen. The guest ants kept their brood in small clusters scattered through the garden and each cluster was cared for by a few workers. Although the ants and their brood were thus intermingled, the workers of each species lavished their attention exclusively on their own eggs, larvae and pupae and were never seen even to transport the progeny of the other species from one part of the garden to another.
The workers and queens of Cepobroticus are rather alert and move about more rapidly than their hosts. They devote so much time to licking and fondling one another that the observer is somewhat astonished to find them paying little or no attention to the fungus-growers. As a rule the two species are indifferent to one another. One may watch them for hours without observing anything more than rather distant, mutual antennal salutations. On rare occasions a worker Cepobroticus may be seen licking the gaster of a Sericomyrmex worker or of the sluggish queen. More frequently one of the host workers may be observed in the act of lavishing similar but more elaborate attentions on a Cepobroticus worker. The fungus-grower begins by licking the feet or tarsi, the tibiae and femora, then the thorax or abdomen and finally the head and even the mandibles of the guest. During this operation the latter remains motionless and inclines its body somewhat to one side.
The Sericomyrmex never feed their guests by regurgitation. This is not surprising because they never feed one another thus, but resort individually to the growing fungus bromatia. When hungry the Cepobroticus workers and queen also crop the fungus mycelium, but they do this rather roughly, using their mandibles and even shaking or disturbing the substratum. The guests very rarely transport or rearrange the particles of the substratum or take the slightest interest in the garden, except as a source of nourishment. Only on one occasion did I see a Cepobroticus carry a particle of the substratum to another spot, insert it and pat it down with her fore feet. When fresh fruit was introduced into the nest, it was much less frequently visited and eaten by the guests than by their hosts.
Brown observed a colony from near Manaus, Brazil (reported as silvestrii in Kempf and Brown 1968; reidentified as symmetochus by Brandao 1990). Brown reported "The colony ... was found in a small rotten log in rain forest on 26.VIII.1962, in a small chamber with a small species of Trachymyrmex. The ants of both species were found throughout the fungus garden of the chamber, but off to one side in a small chamber was found a group of the Trachymyrmex clustered with a small piece of fungus garden unoccupied by Megalomyrmex. ... the situation suggested that the M. silvestrii colony had successfully attacked and moved into the attine nest, and was in the process of plundering it."
Brandao (1990) reported a collection from Belem, PA, Brazil, from a nest of an unidentified Trachymyrmex.
At La Selva, alate queens and males have been collected at blacklights. Males and queens were common at the lab clearing blacklight on 4 Aug 1992. A lone worker was obtained by Ronald Vargas, during general collection of ants from trail surfaces and low vegetation.
Adams, R. M. M., U. G. Mueller, T. R. Schultz, and B. Norden. 2000. Agro-predation: usurpation of attine fungus gardens by Megalomyrmex ants. Naturwissenschaften 87:549-554.
Brandao, C. R. F. 1990. Systematic revision of the Neotropical ant genus Megalomyrmex Forel (Hymenoptera: Formicidae: Myrmicinae), with the description of thirteen new species. Arquivos de Zoologia (Sao Paulo) 31:411-481.
Kempf, W. W., Brown, W. L., Jr. 1968. Report on some Neotropical ant studies. Papeis Avulsos Zool. 22:89-102.
Wheeler, W. M. 1925. A new guest-ant and other new Formicidae from Barro Colorado Island, Panama. Biol. Bull. Mar. Biol. Lab., Woods Hole 49:150-181.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA. firstname.lastname@example.org