Camponotus (Colobopsis) impressus (Roger)

Camponotus impressus, angled view of the head of a queen.
Camponotus impressus, profile view of an alate queen.
Camponotus impressus, frontal view of the head.
Camponotus impressus, frontal view of the head.
Camponotus impressus, angled view of the head.
Camponotus impressus, profile view of a major worker (soldier).
Camponotus impressus, profile view of a major worker (soldier).

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). 

Campontus impressus is in the subgenus Colobopsis. This subgenus 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 impressus can be distinguished from our other two species in this region by metanotal suture of both the major and minor being deeply impressed; the propodeum of the majors usually rounded between faces (angulate in minors); and the angle of truncation of head of major and queen rounded to slightly serrate. In C. mississippiensis and C. obliquus, the metanotal suture of the majors and minors is only shallowly impressed and the propodeum of both majors and minors are angulate between faces. In C. mississippiensis, the angle where the truncation of the head occurs is very sharp with a pronounced rim or flange present and sculpture on the truncated face is very shallow and fine and somewhat shining in overall appearance. C. obliquus has a somewhat serrate, but distinct, ridge separating the truncated portion of the head with the rest of the head. The reticulations of C. obliquus are much larger and more numerous than in C. impressus. In addition, there are many more erect hairs present on the posterior region of the head C. obliquus majors than in C. impressus.

Historically, this species has been confused with C. pylartes fraxinicola, which, according to Bill MacKay (, may not be a valid species. At this time I am going along with the idea that we have three species in AL and MS, C. impressus, C. mississippiensis, and C. obliquus.

In MS, C. impressus has been found nesting in Carya glabra (Mill.) Sweet, Fraxinus americanus L., Solidago spp., and galls produced by the cynipid wasp Callirhytis cornigera (O. S. ) on Quercus falcata Michx. (from Tynes 1964). Tynes, recognized C. pylartes fraxinicola as a distinct species and valid species, however, his records were probably actually C. impressus. He found that species nesting in 21 species of plants in Mississippi including Fraxinus americanus L., Carya illinoensis (Wang.), Carya sp. (hickories), Quercus falcata Michx., Solidago spp., Rhus glabra L., Catalpa speciosa Warder, Berchemia scandens (Hill) K. Koch, Campsis radicans (L.), Sambucus canadensis L., Erianthus ravennae (L.) (plumegrass), Prunus persica (L.) Batsch, Melia azedarach L., Cornus florida L., Crataegus uniflora Meunchh., Ulmus americana L., Smilax sp., Maclura pomifera (Raf.) Schneid., Gleditsia triacanthos L., Vitis labrusca L., and Populus deltoides Marsh (from Tynes 1964).

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