Superstition Mtns Road Trip #5: Part 6
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Sonoran Desert Ants (2)
© W.P. Armstrong 6 February 2013
Ant Images From SW United States & Tropics
Images Of Imported Fire Ants From San Diego
Ant Images From Arizona Trip In October 2012
  Ant Images From The Hawaiian Island Of Maui  
Subfamily Myrmicinae: Leaf-Cutter Ants (Acromyrmex versicolor)

Any discussion of the diversity and natural history of fungi would be incomplete without mentioning the remarkable fungus-growing ants of the New World tropics and Sonoran Desert. There are approximately 12 genera and 210 species of fungus-growing ants in the Attini tribe. Two of the genera, Atta and Acromyrmex are more commonly known as leaf-cutter ants. Leaf-cutter ants are an important forest herbivore because colonies containing millions of ants harvest leaves from a variety of plants for their subterranean gardens of basidiomycete mycelia. The leaves that are harvested by workers and laboriously carried to their nests are not eaten by the ants. Instead, the ants use the leaves as a substrate to grow fungus that they farm in special areas of their nests. The fungus provides the ant colony with a nutrient food source. Special enlarged mycelial structures called gongylida are rich in glycogen. The basidiomycete for Atta cephalotes and Atta sexdens has been identified as Leucoagaricus gongylophorus = Leucocoprinus gongylophorus.

The Atta colony is composed of several castes, including the queen, workers and large soldiers who often stand guard at the entrance of the nest, or even go on scouting missions to protect the colony from predators. Like the queen, the males are winged, and their only role is to inseminate the virgin queen. Workers include larger "media workers" who cut and carry leaf sections back to the nest, and "minima workers" who cut the leaves into minute pieces for the fungus garden. They also cover the leaf fragments with their antibacterial saliva which retards the growth of competing fungi, thus protecting their symbiotic fungus that is vital for their survival. They also feed the entire colony of ants.

Interestingly enough, fruiting bodies (basiocarps) of Leucoagaricus species can be found in urbanized areas of North America, including L. americanus and L. naucinus. The two latter fungi have also been listed in the genus Lepiota.

Leaf-Cutter Ants (Acromyrmex versicolor) In Arizona

Abandoned crater made by desert leaf-cutter ants (Acromyrmex versicolor) The entrance has been caved in, presumedly by heavy rain showers.

Leaf-Cutter Ants Carrying Pinnate Leaves Of Palo Verde

Palo verde (Cercidium microphyllum = Parkinsonia microphylla): State tree of Arizona.

Each bipinnate leaf contains 2 or more pinnate divisions. The ants typically carry one pinnate divison.

Subfamily Myrmicinae: Desert Harvester Ant (Messor)

Harvester ants (Messor) carrying caterpillar (larva) back to nest.

  See Images Of Desert Harvester Ant (Messor pergandei) In California  

Subfamily Dolichoderinae: Orange Desert Ant (Forelius)

Orange desert ant (Forelius).

  See Images Of Orange Desert Ant (Forelius pruinosus) In California  

Arizona's Smallest Ant

Subfamily Formicinae: Rover Ant (Brachymyrmex patagonicus)

A minute rover ant (Brachymyrmex patagonicus) compared in size with a U.S. penny.

The minute rover ant (Brachymyrmex patagonicus) is small enough to slip through the "eye" of an ordinary sewing needle. It's body is only 1 to 1.5 mm in length, comparable in size to a tiny mite.

  See U.S. Penny Size Relationship Used On Wayne's Word  

I saw my first rover ant (Brachymyrmex patagonicus) in Mesa, Arizona in 2013. As of summer 2021, I have encountered this minute ant in San Diego County and throughout southern California. At my home in Twin Oaks Valley this species appears to be tolerated by Argentine ants--at least they coexist in the same area of flagstone along with a third species (Cardiocondyla mauritanica). This species is often called the "black rover ant" because the workers are darker than other species. Its numbers have definitely increased in southern California.

Three naturalized species representing 3 subfamilies of tropical ants sipping honey on a small section of flagstone in my backyard. This makes a grand total of 14 ant species living in my yard. It is amazing what you can find crawling around with a magnifying glass! See Ant Species In My Yard!.

A Tropical Ant That Took Over Biosphere 2 in Oracle, Arizona

Subfamily Formicinae: Long-Horned Crazy Ant (Paratrechina longicornis)

Biosphere 2 is a three acre complex of glass pyramids and geodesic domes with self-contained biomes, including tropical rain forest, grassland savannah, and marine ecosystems. Described as a "planet in a bottle," it was originally constructed in the late 1980s and early 1990s. By 1993 populations of the invasive long-horned crazy ant (Paratrechina longicornis) were discovered inside the supposedly closed ecosystems. The crazy ant is named for its peculiar erratic movements. It is easy to identify with its long legs and very long antennal scape (basal segment of antenna). By the late 1990s, virtually all the ants in Biosphere 2 were Paratrechina longicornis, feeding exclusively on honeydew secretions from scale insects and mealybugs (Order Homoptera) on many of the indoor plants. Biospere 1 is the planet Earth, and its terrestrial ecosystems are impacted by introduced ants. One case in point is the ubiquitous Argentine ant invasion of southern California.

Even with all the safety precautions, including sealed doors and elaborate air-lock system, the Biosphere 2 complex has been invaded by this small, long-legged ant from tropical Asia. It can survive in highly disturbed and artificial areas, including ships at sea. Since it can live indoors with humans, there is no limit to the latitude where it can exist. In fact, it has been reported in human habitats from Sweden to New Zealand, and may be the most widely distributed ant species on earth!

  See The Serious Argentine Ant Dilemma In Southern California  
Argentine Ant HTML Body Background or Wallpaper Design

Mealy bugs (white arrow) on underside of leaf.

Close-up images of Paratrechina longicornis

The legs of this species are also quite long compared with other species with a similar body size, such as the Argentine ant. In fact, this ant can run quite fast and is difficult to catch between your fingers.

Another South American species of crazy ant in the subfamily Formicinae (Nylanderia fulva), is an aggressive exotic species introduced into the southern and southeastern United States. It is called the "tawny crazy ant" or "Rasberry crazy ant," and is named after the exterminator who discovered it in Texas, Tom Rasberry. Like Paratrehcina longicornis it is called a "crazy ant" because of its random (erratic), non-linear movements. Preliminary studies indicate that supercolonies of this species may be displacing the troublesome fire ant (Solenopsis invicta) and may even be a worse pest. Unlike the fire ant, they don't sting; however, they readily invade homes and even damage electrical equipment.

Another Minute Tropical Ant Discovered At Biosphere 2 In Oracle, Arizona
Subfamily Myrmicinae: Flower Ant (Monomorium floricola)

While looking through my vial of "long-horned crazy ants" collected at Biosphere 2, I noticed a tiny ant tangled with one of the Paratrechina longicornis. Its body length was only about 1.6 mm. In fact, when I replaced it in my vial I never saw it again! Maybe I dropped it in the process. Luckily I did get a few images of this fascinating minute ant. It clearly had 2 petiole nodes & small eyes, and keyed down to the subfamily Myrmicinae. Because there were no spines on the thorax, I eliminated all genera except Solenopsis, Monomorium, Strumigenys and Cyphomyrmex. Of the last 4 genera, only Monomorium has a 12 segmented antenna with 3-segmented club. Of course Alex Wild's outstanding images helped a lot, plus I found an excellent article about this species by James L. Wetterer in Myrmecological News stating that it occurred in Biospere 2: J.L. Wetterer, "Worldwide Spread of the Flower Ant, Monomorium floricola (Hymenoptera: Formicidae)." Myrmecological News 13: 19-27, April 2010.

Monomorium floricola: A minute pantropical species discovered in my ant sample from Biosphere 2. Monomorium is similar to the genus Solenopsis, particularly the pharaoh ant (M. pharaonis) and thief ant (S. molesta). In general, Monomorium has a 12-segmented antenna with a 3-segmented club. Solenopsis has a 10-segmented antenna with a 2-segmented club.

Pharaoh ant (Monomorium pharaonis): A troublesome indoor ant found throughout the world. Its common name is derived from ancient Egypt where it may have been one of the insects that plagued this region. It is very similar in size and general appearance to the thief ant (Solenopsis molesta). The two minute species can readily be separated from each other by their antennae if you have a good hand lens or microscope. Attribution: Janke @ en.wikipedia

Big-Headed Ant Minor Worker (Pheidole megacephala) From Maui
I originally thought this was a pharaoh ant (Monomorium pharaonis)

Subfamily Myrmicinae: Pavement Ant (Tetramorium caespitum)

Pavement ant queen (Tetramorium caespitum) in Elkton, Maryland.

Pavement Ant Workers (Tetramorium caespitum) From Truckee, Nevada

Tetramorium caespitum (Pavement Ant): Small, slow-moving ant introduced from Europe.

Unknown sp. From Ontario, Canada

This may be also be Tetramorium. It has propodeal spines, and is not Monomorium. I ruled out Myrmica because the hind tibial spine is not pectinate (see following image). It was sent to me from Orleans, Canada, a suburb of Ottawa, Ontario. This is definitely a species that can survive very cold winters with permafrost.