Myrmobrachys

Blocky Carpenter Ants

Diagnosis: Emery (1925). - "Worker and soldier. - In general small species; dimorphism highly variable; when major difference in head sculpture exists between extreme forms of worker (i.e., between majors and minors, such that majors distinct), little to no transition between castes observed (C. striatus, F. Smith, dimorphus, Emery). Head short: in majors (= soldier), head usually square to trapezoidal in form, somewhat narrowed anteriorly, and with lateral margins somewhat convex; in minors, head markedly narrower anteriorly, with posterior head margin more-or-less straight, and eyes set close to posterior margin (their distance from posterior margin generally less than longitudinal diameter of eye); eyes more prominent among larger workers. Clypeus very convex, if not flat, carinate or ecarinate, broad, with anterior margin convex in minors, relatively narrow, with anterior margin linear or with very short, truncated lobe in majors and soldiers. Frontal carinae strongly divergent posteriorly, sinuate; antennal insertions situated well before midlength of frontal carinae. Mesosoma short; dorsum continuous, arched, or interrupted by notch anterior to propodeum; in latter case, metanotal spiracles visible in dorsal view; pronotum rarely bordered, more often pronotum submarginate or even rounded; mesonotum and propodeum rarely bordered; dorsal and posterior faces of propodeum usually forming curved surface or rounded angle. Petiole squamiform, thin or thick, rarely nodiform. Queen. - Head and clypeus same as in majors or soldiers. Mesosoma somewhat elongate, dorsum depressed: mesoscutum, mesoscutellum, and propodeum at about same level. Male. - More-or-less similar to Colobopsis.

Geographical distribution of the species. Same as that of Myrmaphaenus.

Ethology. - Goeldi observed that C. senex var. textor, Forel, builds nests in leaves using silk secreted by the larvae that the workers hold between their mandibles, just as in Oecophylla. It is likely that other species are practicing the same industry; however, other species inhabit dry branches, spines, etc. (C. planatus var. aacaciae, Emery, C. striatus, F. Smith). This subgenus, as well as the following four (Myrmocladoecus, Myrmeurynota, Myrmodirachis, and Myrmomalis) represent a natural group, distributed throughout the Neotropics, which is characterized chiefly by the head of minors, which, with few exceptions, is wide, posteriorly straight, and with the eyes placed near the posterolateral angles. This group corresponds exactly to the last manipolo of my 1896 classification."

(Translated and edited by B. E. Boudinot, 19 February 2017.)

Myrmobrachys is currently a subgenus of Camponotus.

Species groups of Myrmobrachys
Emery (1925) established three informal species groups within Myrmobrachys, which he defined as follows:

"Group I: senex

Diagnosis. - Worker - Mesosomal dorsum continuous; head of major not or very obtusely subtruncate anteriorly, without major difference in sculpture of minors.

Group II: dimorphus

Diagnosis. - Worker and soldier - Mesosomal dorsum generally interrupted by notch anterior to propodeum (rarely continuous); head of major worker (soldier) more-or-less obtusely truncate anteriorly; most often considerable difference in sculpture exists between major and minor worker head sculpture (Myrmamblys [part], sensu Forel).

Group III: burtoni

Diagnosis. - According to the description, this species can not fit into any of the two preceding groups, because of the fusion of the posterior segments of the mesosoma in majors (soldiers)."

Nomenclature

 *  MYRMOBRACHYS [subgenus of Camponotus]
 * Myrmobrachys Forel, 1912i: 91 [as subgenus of Camponotus]. Type-species: Formica senex, by subsequent designation of Wheeler, W.M. 1913a: 81.