Close-up of P.salinus worker showing surface sculpture.

Looking superficially like a human fingerprint, the costate sculpturing found on the head of Pogonomyrmex salinus consists of a series of fine parallel or sub parallel ridges (rugae), that are rounded at the crest (it requires significant magnification to see the rounded crests).

In P.salinus, the spaces between the rugae appear to be filled with small pits (as can be seen in this image) - this condition is described as punctate. A 1987 study of Pogonomyrmex ants with a Scanning Electron Microscope (SEM), however, suggests that what appear to be pits, are actually the spaces formed by tiny interconnected rugules - a condition, referred to by the authors, as areolate [1] .

Other Pogonomyrmex species, and many other ants, also possess various types of surface sculpturing - the exact form differs from species to species, and is one of the many morphological characters used to identify and classify these, and other ants [2]. These wrinkles and ridges undoubtedly lend a great deal of strength to the ants' armor-like integument (outer body covering).

The sculpturing on the heads of P.salinus ants is often quite rough looking in close-up images - making it seem as though the images have been over-sharpened. This is in contrast to the 'satiny' look of some other species, like Pogonomyrmex wheeleri, and P. bicolor. [IMAGE: Pogonomyrmex salinus worker specimen from central Oregon (050), surface sculpture on head, between right frontal lobe and eye] [scroll down for additional notes/references]

ADDITIONAL NOTES/REFERENCES:

[1]
·Harris, R.A. 1979. A Glossary of Surface Sculpture. California Department of Food and Agriculture, Division of Plant Industry, Laboratory Services/Entomology, No. 28
·Taber, S.W., J.C. Cokendorfer & O.C. Franke.1987. Scanning Electron Microscopic Study of North American Pogonomyrmex (Hymenoptera:Formicidae). Proceedings of the Entomological Society of Washington. 89(3), 1987, pp. 512-526

[2]
·Cole, A.C. 1968. Pogonomyrmex Harvester Ants: A Study of the Genus in North America. Knoxville, University of Tennessee Press
·Fisher, B.L. & S.P. Cover. 2007. Ants of North America: A Guide to the Genera. Berkeley and Los Angeles, CA, University of California Press
·Hölldobler, B. & E.O. Wilson. 1990. The Ants. Cambridge, MA, Belknap/Harvard Press
·Shattuck, S.O. 1987. An Analysis of Geographic Variation in the Pogonomyrmex occidentalis Complex (Hymenoptera: Formicidae) Psyche Vol. 94
·Taber, S.W. 1998. The World of the Harvester Ants. College Station, TX, Texas A&M University Press.