1. Venter of petiolar peduncle (area of ventral process) with one or more distinct setae.

2. Occipital corner with conspicuous rugae or striae.

3. Scape base strongly developed (flared) with a trough or concavity.

In zones of hybridization, Pogonomyrmex harvester ant workers of the southwestern U.S. are hybrids between P. rugosus and P. barbatus. They possess the best genetic traits of two species. The queen of each species mates with the males of opposite species. Sexually mature ants (queens and winged males) are purebreds: They are offspring of queen and males of the same species. Young queens need to mate with their own species to produce more purebred queens. They need to mate with the other species to produce "superorganism" workers. This strategy appears to be evolutionarily advantageous to both species.

If the workers of an ant nest can be thought of as the superorganism's body, and the sexuals (queens & males) can be thought of as the superorganism's genetic material, it is as though an animal with the body of a mule has the genetic make-up of a horse and donkey!

Although Pogonomyrmex hybrid workers form a colony and the mule is a single organism, they make an interesting comparison. They both involve a cross between two species that forms a stronger hybrid offspring with the best traits of its parents. The ant colony of hybrid workers functions as a unit that could be described as a "superorganism." This is similar to the "Borg Collective" in Star Strek: The Next Generation.

The female horse (mare) mates with a male horse (stallion) to produce more male and female horses. If she mates with a male donkey (jackass) she can produce a male or female mule. The mule is a sterile hybrid with the body size of a horse and the sure-footedness and endurance of a donkey. That is why the mule is essentially a "superorganism" used as a powerful pack animal. In the case of Pogonomyrmex, the hybrid "super-ants" are the workers!

An original 20 mule team wagon train used in 1885 to haul borax from Death Valley to Mojave, a distance of 165 miles. The borax weighed 24 tons and the entire wagon train weighed 36.5 tons (gross weight). The 3rd wagon carried water for the mules during the hot, 10 day journey across the Mojave Desert. Today, a load of this size would be pulled by a 600 horse power Kenworth T-2000 tractor with an air conditioned cab!