Ant of the Week: Trachymyrmex arizonensis

The ant of the week is one of those amazing ants not many people get to see.

Photograph by Michael Branstetter / © / CC-BY-SA-3.0 from Wikimedia

You can probably tell right away that this worker is a leafcutter in the tribe Attini because of the spines and spikes. Ants in the genus Trachymyrmex grow a fungus garden like other attines, although they are much more likely to collect plant debris from the ground for their gardens than actually cut fresh leaves. They are the original composters.

Photograph by April Nobile / © / CC-BY-SA-3.0 from Wikimedia

The bumps, called “tubercules,” are characteristic of the group. Trachymyrmex arizonensis is known for the prominent tubercules on the first tergite of the gaster, as well as by the shape of the carinae (ridges on the front of the head). (See Rhabling, et. al. 2007). Unlike the spectacular polymorphism of Atta leafcutters, the workers are mostly monomorphic in Trachymyrmex.

Several species, including Trachymyrmex arizonensis, live in southeastern Arizona in the more mountainous regions. All members of Trachymyrmex are found in the New World.

Colonies are relatively small, with mature colonies up to about 1000 workers. Most Trachymyrmex nests are pretty much unnoticeable, but T. arizonensis does produce a yellowish mound. (You can be sure I will be on the lookout for those from now on.)

Are you bothered by the dust and debris on the ant in the photograph? Entomologists have long noticed that Acromyrmex ants are covered with fuzz, which looks a bit like dander. Because most ants are shiny clean, Cameron Currie decided to examine the debris closer. The fluff turned out to be bacteria. Not a disease-causing bacteria, but unusual bacteria capable of making its own antibiotics. When leafcutter ants grow the fungus they use as food, parasitic and competing fungi are a constant threat to their underground gardens. While the workers tend their gardens they distribute the helpful bacteria from their bodies, which inhibit the growth of harmful bacteria and fungi. There have even been suggestions that leafcutter workers have those unique crevices and bumps on their bodies as places for the helpful bacteria to grow. Given the whitish appearance in some of the photographs online, it is very possible that Trachymyrmex has its own bacteria, (although Dale Ward identifies it as a mineral deposit.)

Does anyone have a colony of these ants? Anyone working on Trachymyrmex? I would love to learn more about them.


C. Rabeling, S. P. Cover, R. A. Johnson, and U. G. Mueller. (2007) A review of the North American species of the fungus-gardening ant genus Trachymyrmex (Hymenoptera: Formicidae). Zootaxa. 1664: 1–53. There is a link to a free .pdf in this list of publications. (Encyclopedia of Life also has the key).

Bert Hölldobler and E.O. Wilson. 2011. The Leafcutter Ants. W. W. Norton & Company, New York. (More info at previous post.)

Dale Ward has a nice series of photographs with captions at Ants of the Southwestern United States.

Alex Wild of Myrmecos also has a number of photographs, including one of a tiny species, Pyramica arizonica, that lives in the nests.

Mingzi M Zhang, Michael Poulsen, and Cameron R Currie. (2007). Symbiont recognition of mutualistic bacteria by Acromyrmex leaf-cutting ants. The ISME Journal. 1: 313–320

Ant of the Week: Pogonomyrmex californicus

Pogonomyrmex californicus is a common harvester ant in the Sonoran Desert.


Ants of the genus Pogonomyrmex are generally easy to recognize by the presence of a psammophore, a series of long hairs resembling a beard on the underside of the head. In fact, the root of its name “pogono” means beard in Greek.

The species can be distinguished from others in the genus by the fact it lacks propodeal spines (spines on the back of the trunk). The color varies throughout the southwestern United States. BugGuide has a collection of photographs of Pogonomyrmex californicus, including some that look just like the ones shown here.


Like other harvester ants, the diet of Pogonomyrmex californicus consists mainly of seeds from nearby plants, although they will also scavenge dead arthropods. The seeds are processed and stored within the nest.

Unlike the fire ants, which forage in groups, the Pogonomyrmex californicus workers are often seen foraging singly, gaster held straight out behind.

Pogonomyrmex californicus is found in open areas, often in association with Dorymyrmex bicolor.

At least where human activity is high, the Dorymyrmex seem to predominate. See the dead harvester next to this mound?

Pogonomyrmex californicus queens may work together to form new nests, as shown in the video. Although some seem to be “working” together more than others. 🙂

Why do you think the one queen is vibrating her gaster? Is that why the other queens take off?

Obviously there are a lot of interesting things still left to be discovered about these ants.

For more information see:

Navajo Ant Project

List of North American Pogonomyrmex at ASU

Robert A. Johnson. (2004). Colony founding by pleometrosis in the semiclaustral seed-harvester ant Pogonomyrmex californicus (Hymenoptera: Formicidae). Animal Behaviour. 68(5): 1189-1200.

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Ant of the Week: Weaver Ants

As you probably know, spiders and birds aren’t the only ones who know how to weave. Weaver ants (mostly ants of the genus Oecophylla) are named because the worker ants use silk produced by their larvae to sew or weave together leaves in trees to make a nest to live in.

Photo by Robin Klein at Wikimedia

To do this, worker ants form a living chain between nearby leaves in a tree and bring leaf edges together. Other workers carry the legless larvae to the edges and give them the signal to spit up silk. As the worker ants move the larvae back and forth, the leaves are bound together into a cluster. The ants use the leafy clusters as nests.

This video shows the workers in action.

Weaver ants are elegant, long-legged ants.

Photo source Sean.hoyland at Wikimedia

Some species of weaver ants are also known as green ants due to the greenish color of their rear sections (gasters). They are called citrus ants or orange ants because they are used to protect fruit in citrus orchards. Weaver ants guard their homes with vigor and attack and eat any arthropods in the vicinity.

Photograph by Axel Rouvin at Wikimedia

As far as is known, the ancient Chinese were the first to use these ants to control pests and protect crops. Around 1,700 years ago, farmers employed weaver ants to keep caterpillars, stink bugs and small rodents out of their valuable citrus orchards. Farmers could stroll down to their local market, buy ant nests full of ants and put them out into their orchards. Evidence suggests the farmers actually provided platforms or runways so the weaver ants could run from tree to tree.

So, that’s ancient history, right? Those were times before pesticides and modern technology. Who needs ants now?

In fact, in the later part of the twentieth century many growers did switch to using pesticides to protect their crops. Soon, because of the high costs of pesticides, and other problems associated with pesticide use, farmers quit using them and began using ants again in their orchards. Today farmers in Asia and Northern Australia rely on weaver ants to control pests of mango, coconut, oil palm and cashew orchards.

I would love to see weaver ants in real life someday. They are amazing.

Have you ever seen weaver ants in action?


There is a children’s book that describes the ancient Chinese practice of using weaver ants in orchards called Ma Jiang & The Orange Ants by Barbara Ann Porte and illustrated by Annie Cannon.

Ant of the Week: Southern Fire Ant

The first thing you notice about workers of the Southern fire ant, Solenopsis xyloni, is what fierce foragers they are.

You never see just one foraging worker. Instead, there’s almost always a teeming mass.

Even when they are collecting sweets at extrafloral nectaries, Southern fire ants show up in greater numbers than most other species.

Southern fire ants are thought to be originally from throughout the southern and western United States. They have been displaced in many areas by the imported fire ant, Solenopsis invicta, but still occur widely in the dry areas of Arizona and California.


Solenopsis ants are relatively easy to tell from other ants because of the antennae have ten segments with a two-segmented swollen area or  “club” at the end.

Solenopsis xyloni workers vary considerably in size and color, even within colonies. The larger workers tend to have lighter-colored heads and trunks than the smaller workers. In the area around Phoenix, Arizona, the Southern fire ants seem darker than those found elsewhere.

(These workers are feeding on their favorite meal of dried cat food.)

Where Solenopsis xyloni and S. invicta overlap it is difficult to distinguish the two species. Jacobson et. al. (2006) have developed a pcr technique and guidelines for identification (see references).

To make things even more confusing, it seems that Solenopsis xyloni hybridizes with Solenopsis geminata where the two overlap.  Obviously this group is “interesting” from a taxonomic standpoint.

The foraging workers are often seen carrying bits of hard food or arthropod parts back to the nest. They also gather some seeds.

Wet food, like this watermelon, go straight to the crop.

Often the foraging trails around their nests are underground or partially covered, so you might not notice them until you dig into the soil or pull up a weed. Then they come boiling up seemingly out of nowhere.

When foragers cross a man-made structure, such as a walking trail, sidewalk, or tile floor, they form a dense foraging trail of numerous workers traveling in both directions.

You have to admire the ability of Southern fire ants to find, process and transport food very rapidly. Plus they seem to eat just about anything they encounter. It is no wonder the colonies can grow to a relatively large size.

Do you have fire ants where you live? Have you ever watched them gather food?


Solenopsis xyloni by Dale Ward

The Navajo Ant Project has a brief review of taxonomy

Ant Web shows some of the color variation within the species

Jacobson AL, Thompson DC, Murray L, Hanson SF. (2006). Establishing guidelines to improve identification of fire ants Solenopsis xyloni and Solenopsis invicta. J Econ Entomol. 99(2): 313-22.

Trager, J. C. (1991). A revision of the fire ants, Solenopsis geminata group (Hymenoptera: Formicidae, Myrmicinae).  Journal of the New York Entomological Society. 99 :141-198.