Ants of Arizona: A Glimpse

Arizona wasn’t always a prime target on my travel list. However, that all changed last year when I heard about the “Ants of the Southwest” course offered at the Southwestern Research Station near Portal, AZ. This course would teach essential myrmecology skills to an eclectic group of keen enthusiasts while sampling some of the 350 local ant species. It would also bring us to a range of habitats across an impressive altitudinal gradient; from the Chihuahuan Desert floor to the sky islands of the Sierra Madre. I now had to go to Arizona. Thus, I attended the 2018 edition of the course, which was hosted by Michelle Lanan, Clint Penick, and Christina Kwapich. Here are some of my favorite ant (and other critter) encounters from the trip.

A Photoblog contribution by François Brassard

Please note: All pictures are copyright by François Brassard (© François Brassard)

Nested in the mountains, the Southwestern Research Station harbors a mixture of ant species typically found in temperate forests or arid habitats.

Emblematic Ant Species

Here is a portrait of a harvester ant (Pogonomyrmex sp.). You can observe these charismatic ants in arid areas of the American Southwest. However, beware of their painful sting.

Ants in the genus Pogonomyrmex have long coarse hairs (i.e. psammophores) on the underside of their heads, which gives them a bearded look. This “beard” facilitates carrying fine sand while excavating their nests.

Ants in the genus Acromyrmex are true leaf-cutters that grow fungus within their nests. However, unlike the more well-known Atta ants, they prefer flowers and fruits to leaves. This leaf-cutter (Acromyrmex versicolor) is distinct from other Acromyrmex species since it inhabits deserts, whereas most species inhabit moist tropical forests.

Despite being one of the most widespread ant genera in the world, Monomorium often go unnoticed because of their small size (i.e. 1 – 2 mm).

Here is a portrait of a winnow ant (Aphaenogaster sp.) on a dry riverbank. These ants have an almost worldwide distribution and vary extensively in their morphology. However, North American species can be distinguished by their long head, elongate mesonotum and poorly defined antennal club. Some species are important dispersers of seeds bearing elaiosomes, a process known as myrmecochory.

Acrobat ants (Crematogaster) are easily identified by their heart-shaped gasters. These dozens of workers were making a meal out of a large caterpillar that fell on the desert floor.

Honeypot ants (Myrmecocystus sp.) are found in arid areas of the U.S. and Mexico. They are well known for the ability of workers to store sweet liquids.

While visiting Ray Mendez’s workshop, he gave us an inside look of a honeypot ant colony (Myrmecocystus sp.). The workers with the large gasters are called ‘repletes’ and function as living food-storage units. These ants may contain sweet liquids and are considered a treat in some cultures. However, Roberta Gibson recently informed me that repletes may also contain liquids scavenged from dead invertebrates such as earthworms. As such, if you dare to eat one you may get some extra non-ant proteins in addition to your sugar fix. In any case, the importance of repletes for ants is that they contain large energy reserves that the colony can use in times of need.

Carpenter ants are polymorphic; they have multiple worker castes with distinct morphologies. This major and minor worker of Camponotus sp. (notice the larger head of the major) were feeding on a tree baited with honey.

• 

• 

The genus Dorymyrmex can be readily recognized from other dolichoderines by its pointy propodeum. Like all ants within the Dolichoderinae subfamily, they do not have a sting, but instead have anal glands that produce a strong odor, sometimes compared to the smell of blue cheese.

Citronella ants (Lasius sp.) are less conspicuous than more familiar Lasius species because of their more subterranean habits. However, if you’re lucky, you may find a nest of these golden-colored ants by lifting a few rocks in deciduous and mixed forests.

The genus Lasius is very common across the Holarctic. However, they can also be found in the American Southwest in the coniferous forests located at higher altitudes. This worker is picking up eggs to relocate them after her nest was disturbed.

Ants in the genus Nylanderia are generalist feeders that can be found almost worldwide. I found this worker foraging at night in an arid habitat.

Ants, like this Novomessor on a cactus, can often be found foraging for nectar in flowers.

Workers of the genus Pheidole are often dimorphic, where the larger caste (i.e. majors) have disproportionately larger heads than the smaller caste (i.e. minors). In Pheidole the majors are commonly called soldiers.

Solenopsis_sp: These Solenopsis ants were nesting under dung. Looking under dung piles can yield interesting ant species. Potentially because they offer a better buffer from the arid conditions of the desert.

Ant-ant interactions

An ant’s fiercest competitor is often other ants. This is evident in the desert, where you can easily observe ant competing. For instance, I found these two workers, one Novomessor and one Pogonomyrmex, interacting aggressively at a nest entrance .

Army ants encompass more than 200 species across different lineages, meaning that this nomadic behaviour evolved multiple times. Here, two species of Neivamyrmex are preying upon much larger opponents (Camponotus and Pogonomyrmex) by swarming them.

Forelius_nest_evacuation: With army ants in the surrounding area, this Forelius colony declared retreat and evacuated their nest. Even the brood and the queen were being frantically transported on the desert floor.

Interspecific competition in ants is high on the desert floor at night. In this photograph, honeypot ants (Myrmecocystus) attack a Pogonomyrmex worker.

Polyergus ants are obligate slave-makers of Formica ants. These workers were part of a raid where hundreds of Polyergus intended to steal brood from a host colony.

Ant interactions with other insects and critters

Ants love their carbohydrates. I have found this to be especially true for formicines. As such, one way to find wood ants and carpenter ants is to find plants with extrafloral nectaries, or sap-feeding insects that expel their excess sugar as honeydew. You can almost be sure to find a formicine frolicking nearby, like these Formica workers tending a scale-insect.

Caught by surprise; a jumping spider (Salticidae) is preying on a trap-jaw ant queen (Odontomachus sp.). Only a few queens succeed in founding a colony. This one did not.

Similarly, this Camponotus queen fell prey to a scorpion.

Blind snakes, also called worm snakes, are within the family Leptotyphlopidae. They are specialist predators of ants, which they find by tracking their pheromone trails.

Hundreds of Pheidole workers were crawling on this vinegaroon (whip scorpion) carcass .

Ants are sometimes called nature’s garbage collectors. Indeed, dead arthropods laying in the leaf litter rarely go unnoticed for long. Here, a Formica worker carries the remains of an isopod back to her nest.

I highly recommend visiting Arizona’s diverse ecosystems, and if you are interested in myrmecology definitely look into the “Ants of the Southwest” course.