Arizona Road Trip Jan-Feb 2016 Part 5
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Arizona Road Trip Jan-Feb 2016 Part 5
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Ant Species (1)

Army Ant (Neivamyrmex) On Superstition Mountain (The Superstitions)

For the past 4 years I have searched for this genus near my home in San Marcos, California. They have been collected in traps In San Diego and Orange Counties and throughout Arizona. On January 30, 2016, I looked under a rock on the west slope of Superstition Mountain, Arizona and noticed some minute yellowish or amber-colored ants without eyes. The smallest workers were about 1.5 mm and the largest were about 2.4 mm. I was expecting larger ants for this genus. Army ants typically form temporary camps (bivouacs) instead of permanent nests.

The army ants were bivouacked under the rock in foreground (white arrow) on 30 January 2016. Two days later there was no sign of them at this location.

When the rock was lifted these tiny ants were scurrying in all directions into subteranean cavities.

Minute worker army ants (Neivamyrmex) from under a rock on Superstition Mountain. Based on the description and key to Neivamyrmex in (and their small size), they appear to be N. nyensis or possibly N. leonardi. These seldom seen species are described as subterranean in some references. According to Gordon Snelling, Neivamyrmex authority (personal communication, 2016), they are close to N. nyensis, although "the mandible is a bit off." Gordon Snelling (Personal Communication, 26 Jan. 2017), it is N. leonardi!

Army ant worker (Neivamyrmex) from under a rock on Superstition Mountain. Based on the description and key to Neivamyrmex in (and small size), it may be N. nyensis, a seldom observed species. According to Neivamyrmex authority Gordon Snelling (Personal Communication, 26 Jan. 2017), it is N. leonardi! Key To Neivamyrmex Species   

Inexpensive Way To Manipulate Tiny Ants In The Field

Simply pick up the ant with a fine-tipped paintbrush. The ant can be turned and photographed from different directions. I have used this method for many years with my duckweed (subfamily Lemnoideae) identifications. It is especially useful with Wolffia species, the world's smallest flowering plants.

I have been able to see most of the characteristics mentioned in the Neivamyrmex key by Gordon Snelling. If the petiole node is no longer than broad or only slightly so, it could be Neivamyrmex leonardi. If the petiole node is distinctly longer than broad, it could be N. nyensis. According to Neivamyrmex authority Gordon Snelling (Personal Communication, 26 Jan. 2017), it is N. leonardi!

Army ants are notorious for their raids of ant colonies of other species. Army ants of the genus Neivamyrmex are well known for their raids on nests of Pheidole, small harvester ants that are common in deserts of the southwestern U.S. The subterranean N. leonardi is known to raid nests of Pheidole obtusospinosa. There has apparently been strong selection pressure on these minute desert Pheidole (with workers only 2 mm long) to evolve major workers (soldiers) with very large heads in proportion to their bodies. In fact, Pheidole species are known as big-headed ants. Some species of Pheidole have super majors (super soldiers) with exceptionally large heads. According to Ming H. Huang (2010), super majors of P. obtusospinosa were involved in blocking the nest entrance with their enlarged heads.

Huang, Ming H. 2010. "Multi-Phase Defense by the Big-Headed Ant, Pheidole obtusospinosa, Against Raiding Army Ants." Journal of Insect Science Vol. 10: DOI:

  Alex Wild's Photo Of Pheidole tepicana Super Major  

In our southwest desert, tiny Pheidole ants have major workers to defend their nest against army ant raids. The major worker has an enormous head in proportion to its body. Some species actually block the nest entrance with their heads!

  Antwiki Key To The Pheidole Pilifera Group  

Minute Forelius Ants On Superstition Mountain

Ants of the genus Forelius (F. pruinosus & F. mccooki) are similar to Neivamyrmex in size and color. They occur under nearby rocks in the Superstitions, so you must look very carefully. Under magnification they are pretty easy to distiguish: Forelius have one petiole node and eyes. The small burs are from seed heads of triangle leaf bur-sage (Ambrosia deltodea), a dominant shrub in this area.

To get an idea of how small the worker of Forelius pruinosus really is I have compared it with grains of ordinary table salt (NaCl). An average cubical grain is about 0.3 mm on a side. For their small size, these minute ants run very fast.

  Forelius on Owens Peak   

Big-Headed Ant (Pheidole) On Superstition Mountain

Two nests of minute minor workers of big-headed ants (Pheidole) near the common mediterranean grass Schismus. Both S. barbatus and S. arabicus occur in the Superstitions.

  SEINet Plants Of The Superstitions by K.C. Rice  

The heads of major workers appear quite reddish. They are similar to the colonies found near Willcox, Arizona

  Big-Headed Ants Near Wilcox, Arizona  

Myrmicinae: Dark Southern Fire Ant (Solenopsis xyloni)

The native fire ants (Solenopsis xyloni) in the Superstitions are very dark, unlike the distinctive red and black fire ants on Owens Peak.