Salton Sea Part 6
Wayne's Word Index Noteworthy Plants Trivia Lemnaceae Biology 101 Botany Scenic Wildflowers Trains Spiders & Insects Search
Salton Sea January 2015 Part 6
     Home        Part 1        Part 2        Part 3        Part 4        Part 5        Part 6        Part 7  
Minute Big-Headed Ant (Pheidole) At Dos Palmas Preserve

Professor E.O. Wilson has written an entire book about Pheidole ants of the New World. The book includes 624 species, with an estimated 1500 species worldwide! In the sand near Dos Palmas I discovered minute Pheidole minor workers only about 2.0 mm long! Pheidole barbata has been reported from Dos Palmas and this minute ant is very similar to the species I found.

The small nest in the sand is very difficult to spot, especially in the late afternoon. I had to literally get down on my knees and crawl. Most of the small craters I found were nests of a black Dorymyrmex.

The minor workers in above image are not much larger than the grains of sand.

Familiar Objects To Appreciate The Small Size of This Ant

The Pheidole ant is not much larger than seated Lincoln!

1.5 mm = Diameter of pin head & U.S. Penny used in Wayne's Word articles.

Two Pheidole ants compared with the head of an ordinary straight pin. This species appears to be P. barbata. In fact, P. barbata has been collected from Dos Palmas Preserve north of the Salton Sea where I found these specimens.

Pheidole barbata: Major occiput smooth and shiny without carinulae or rugulae. Propodial spines absent from majors and minors. It also appears to have long, course hairs on ventral side of head called a psammophore (see below). Antwiki Key To The Pheidole pilifera Group

Some of the following is from Pheidole (pilifera-group) barbata: Derivation of the specific epithet barbata: "Bearded," alluding to the long, coarse hairs on the ventral head surface of the minor. A member of the "bicarinata complex" of the larger pilifera group, comprising agricola, aurea, barbata, bicarinata, centeotl, cerebrosior, defecta, gilvescens, macclendoni, macrops , marcidula, paiute, pinealis, psammophila, vinelandica, xerophila, yaqui, and yucatana (barbata is closest to psammophila). P. psammophila is characterized by a psammophore, a basket-like enclosure of hairs on ventral surface of head, used to carry sand or other loose particles. It is apparently an adaptation to its habitat of loose and shifting sand. I did not observe a distinct psammophore in my sample of P. barbata. In addition, P. barbata is distinguished by the absence of propodeal spines in both castes.

Dorsal view of Pheidole barbata; however, there are some very similar species.

Ventral view of the head of Pheidole barbata. There are long hairs on ventral side of head, but I cannot distinguish a distinct psammophore in this poor image taken with a dissecting microscope.

Have you ever tried to pick up dry, loose sand with fine-tipped forceps? This desert ant is adapted to soft, loose sand. Sand spilling out of mandibles is caught in the long hairs on underside of its head.

Illustration of a psammophore in Pheidole psammophila. Here is an analogy to explain the purpose of a psammophore: Comparing the mandibles of Pheidole with tweezers, have you ever tried to pick up loose, dry sand with fine-tipped tweezers or forceps?

In one nest I found partial exoskeletons of heads of five larger ants and one large mandible. Are these the heads of majors? Were they killed by the minors as postulated by W.M. Wheeler for Pheidole militicida ("Some Additions To The North American Ant Fauna." Bull. Amer. Mus. Nat. Hist. Vol. 34: 389-421, 1915) and later discounted by W.S. Creighton & R.E. Gregg ("New and Little-Known Species of Pheidole (Hymenoptera: Formicidae) from the Southwestern United States and Northern Mexico," Univ. Colo. Stud. Ser. Biol. Vol. 3: 1-46, 1955)?

    "It appears, therefore, that all the individuals of this caste (the majors) are regularly killed off by the workers on the approach of winter, probably after they have broken open all the hard seeds collected by the workers. Such a slaughter of the members of a large caste during the season when their activities are no longer required, when they would simply be a burden on the colony by consuming stored food and when fresh food cannot be collected, must have great advantages. Although I have never noticed this behavior in other species of Pheidole, I believe that a study of the harvesting species with very large-headed soldiers in the deserts of the southwest may bring other similar cases to light." W.M. Wheeler (1915).

Since I could not find any intact majors, I attempted to reassemble (using Photoshop) the head from exoskeleton parts recovered from the nest. Assuming these are from the true major caste for this species, the image shows an enormous difference in the head sizes for major and minor workers.