Subfamily FORMICINAE
Tribe CAMPONOTINI

Camponotus (Colobopsis) obliquus M. R. Smith

Camponotus obliquus, slightly angled view of the head of a major worker.
Camponotus obliquus, profile view of a major worker.

Ants in the genus Camponotus are collectively known as carpenter ants because some species nest in wood, including man-made structure. This genus includes some of the largest and most common ants in the world, and they are found in all biogeographical regions (Bolton, 1995).  More than 900 species of Camponotus are known worldwide, with 50 species reported from the United States (Hanson and Klotz, 2005), and 20 species found east of the Mississippi River (Deyrup, 2003; Smith, 1979). 

Species in this genus are variable in size with workers ranging in size from 3 to 15 mm or more in length and queens (also referred to as females) of some species attaining a length of 19 mm or more. Many species are polymorphic. Workers have a 12-segmented antenna that lacks an apical club. Antennal fossae do not touch the posterior border of the clypeus. Ocelli are not present on the heads of workers. The workers of most species have an indistinct metanotal suture between the promesonotum and the propodeum, although this suture is present in C. sexguttatus and some members of the subgenus Colobopsis.  Those species that lack the obvoius and deep metanotal suture have the shape of the alitrunk in a smoothly curved arc (as seen in profile). 

Camponotus obliquus is in the subgenus Colobopsis, whose members can be distinguished from other carpenter ants by the unusual modifications of the heads of both the major workers and queens which are severely truncated in the anterior third. This phragmotic condition enables the major workers to serve as living doors to their nests which are in living or dead twigs, stems, and some galls.

Camponotus obliquus, in the subgenus Colobopsis, is a relatively small Camponotus species with majors ranging in length from 3.5 to 3.75 mm. The angle of the truncated area of head of majors is somewhat serrate in appearance. The truncated area of head of major and queen has very coarse and relatively large foveolate punctures or reticulations, which are also present on the sides of the head to the eyes. The alitrunk of the minors is dark reddish brown in color. This species most closely resembles C. impressus, by which is differs in having larger and sharper reticulations in the truncated area; more and coarser reticulations on the side of the head; and more erect hairs on the posterior area of the head. Additionally, the metanotal suture of the majors and minors of C. obliquus is only shallowly impressed and the propodeum of both majors and minors are angulate between the faces. Camponotus mississippiensis is the only other species in this subgenus likely to be found in this area and it differs from C. obliquus by the majors having a sharp edged rim at the point where the side of the head meets the truncated face of the head. Camponotus mississippiensis also differs by having very fine sculpture and even appearing somewhat shining in the truncated area of the head, rather than having coarse sculpture.

Little is known about the biology of this species, but it is likely to have similar nesting habits as C. impressus and nest in a variety of twigs and branches, galls, vines, etc. I have collected it nesting in Berchemia scandens (rattan vine).

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