● NW of Mattawa [Grant Co], WA USA [el. 152 m / 500 ft] view location in Google Maps »
● 9/27/09 9:47AM sunny, air temp: 18°C / 65°F
The bleached exoskeleton of a Pogonomyrmex salinus worker, on the edge of a Pheidole creightoni nest, in central Washington state. Along with plant debris, we have observed large numbers of P. salinus carcasses, and body parts in the refuse piles (middens) surrounding/covering these Pheidole nests. Occasionally, we see the remains of other insects (including other ant species) along with the Pogos. The remains of a Tetramorium worker can also be seen at the right edge of this image. [scroll down for additional notes/references]
We have found Pheidole creightoni living in close proximity to P. salinus at a location in central Washington state. In one instance, the distance between the entrances of a large P. salinus nest, and a Pheidole creightoni nest, was measured at 1.4m / 59 in., and at least two P. creightoni nests appeared to be built on the abandoned remnants of P. salinus mounds. The Pheidole nests are (at least in some cases) in the form of a small gravel crater, often with much chaff and Pogo carcasses present.
On one occasion (9/27/09) we observed Pheidole creightoni major and minor workers foraging on the gravel portions of a large, low, active Pogonomyrmex salinus nest mound. The Pogo workers appeared to take no notice of the tiny trespassers. A few of the Pheidole workers picked up small pieces of plant matter, and headed back toward their nest. A 'foraging party' (consisting of one major, and six minors) was also seen emerging from the Pheidole nest, in 'single file' (though not traveling toward the P. salinus mound, but in a different direction).
W.S. Creighton observed this ant (P. creightoni) near Applegate, Oregon, nesting in close association with the ant Messor andrei (an ant somewhat similar to P. salinus in appearance and habits). He noted that the Pheidole nests were ringed with chaff (discarded seed/plant debris) indicating that seeds were probably an important part of their diet (he also fed then freshly-killed squirrel meat, which they accepted). As mentioned above, we also see large amounts of chaff around/on P. creightoni nests, with the addition of Pogonomyrmex salinus body parts and carcasses (and rarely other ant/insect parts), indicating a possible reliance on scavenged insects, in addition to seeds, as a food source. Since some of the Pheidole creightoni nests that we have observed seem to be built on/very near the sites of abandoned Pogo colonies, we think it is possible that some of these carcasses are brought up from below by excavating P. creightoni workers. We will observe these ants more thoroughly in our 2010 season.
The Pheidole creightoni workers pictured here were differentiated from the very similar species, Pheidole californica, by the following characters: postpetiole of major 'spinose' in dorsal view; lateral cephalic setea of major, short and erect/nearly erect, in face-on view; propodeal spines of major in the form of 'long blunt pegs'; postpetiole of minor 'trapezoidal' in dorsal view.
·Burge, D.O. 2005. Taxonomy, Biology, and Distribution of Seed Harvesting Ants in the Pheidole californica Complex (Hymenoptera: Formicidae)
·Gregg, R.E. 1955. A New Species of Ant Belonging to the Pheidole Pilifera Complex (Hymenoptera: Formicidae). Psyche, Vol. 62, No.1, March, 1955
·Wilson, E.O. 2003. Pheidole in the New World: A Dominant Hyperdiverse Ant Genus. Harvard University Press, Cambridge, Massachusetts