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Sometimes projects get interrupted, for example my attempt a few years ago to learn all the species of Pogonomyrmex harvester ants in Arizona. But just because there has been an interruption, doesn't mean the project will never be finished. Today let's take a look at the Maricopa harvester ant,  Pogonomyrmex  maricopa.

Pogonomyrmex-maricopa-227-crpped

Two things are apparent about these ants right away. The first is they are active at high temperatures. The day this photograph was taken the air temp reached a high of 104° F, and ants like Novomessor had disappeared into their nests by early morning. In contrast, these Maricopa harvesters were still going strong by mid-morning.

a-Pogonomyrmex-maricopa_0251

The second thing that is apparent is Pogonomyrmex maricopa workers tend to hold their metasomas (gasters or rear sections) high in the air while walking or running. Pogonomyrmex californicus workers also do this. In this area P. californicus is quite distinct because the workers have dark metasomas and are found at lower elevations.  In other regions the colors and ranges overlap and the two species can be hard to tell apart. AntWiki has a quote from Cole's book about how to distinguish them.

By the way, the photographs for this post aren't the highest quality. That is because a prudent photographer keeps his or her distance from Pogonomyrmex  maricopa workers. Their most prominent claim to fame (or notoriety) is that Maricopa harvester ant workers produce the most toxic insect venom investigated so far (Meyer, 1996).

This species also has an unusual sting. The sting is barbed and can pull out of the ant's metasoma to be left behind within a mammalian victim pumping venom like a honey bee sting does.  It is best to give them plenty of space, although of course Alex Wild has a nice close-up shot.

Pogonomyrmex-maricopa-midden-0281

Harvester ants are known for collecting seeds from plants, but it is always interesting to look at what the ants have discarded in their middens. As well as various seeds, this midden has the exoskeletons of isopods. The needles and eucalyptus leaves are from nearby trees.

Pogonomyrmex-maricopa-midden-a-288In addition to more isopod exoskeletons, other piles had seed husks, beetle elytra and a few feathers.

harvesters-Pogonomyrmex-maricopa

Although they don't make a big mound of pebbles around their nest like some other desert ants, Maricopa harvester ants have been found to bring calcium carbonate to the surface causing a "cement cap" to form, which stabilizes the area around the nest entrance in sandy areas (Whitford 2003). Sounds like some interesting chemistry going on.

Pogonomyrmex  maricopa is a common and intriguing species of harvester ants. Hopefully we will learn more about them soon.

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According to Antweb, there are 15 species of Pogonomyrmex in Arizona (links go to Wild About Ants posts as they are added):

  • Pogonomyrmex anergismus
  • Pogonomyrmex  apache
  • Pogonomyrmex barbatus
  • Pogonomyrmex bicolor
  • Pogonomyrmex californicus
  • Pogonomyrmex (occidentalis-group) colei
  • Pogonomyrmex  desertorum
  • Pogonomyrmex hoelldobleri
  • Pogonomyrmex huachucanus
  • Pogonomyrmex (Ephebomyrmex) imberbiculus
  • Pogonomyrmex (californicus-group) magnacanthus
  • Pogonomyrmex  maricopa
  • Pogonomyrmex  occidentalis
  • Pogonomyrmex pima
  • Pogonomyrmex  rugosus

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Remember that  Pogonomyrmex nest with the shiny black spots around the nest entrances from a few weeks back?

 

black-spots-another-view

This one?

Upon revisiting a few weeks later, the ants are looking better.

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They seem to have cleaned up nicely.

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Maybe there are a few spots left, but nothing like before.

pogos-gathering-food

What are they harvesting today? You probably recognize the beetle elytra, but what is the gray cylinder?

pogos-with-screwbean-mesquite

You might need to be from Arizona to recognize it. That is part of a seed pod from a tree with the common name "screwbean mesquite."

Wonder what they will be up to next time I visit.

What kind of ants do you visit regularly?

While visiting a local park this week, I stopped by to visit a Pogonomyrmex nest I have been watching over the years.

black-spots-around-harvester-ant-nest

I almost immediately noticed the black spots around the nest entrances.

black-spots-around-harvester-ant-nest-another

Here's another entrance about 20 inches from the first two. There was a noticeable blackening around the hole in comparison to the surroundings. Otherwise, the ants seemed to be active and doing fine.

black-spots-another-view

This is a closer view.

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Looks kind of shiny.

My first thought was ant feces. Studies have shown that some ants mark their nest areas with feces, for example a study by Grasso et al. (2005).

black-spots-33

My other guess is that someone tried pouring something into the nest (as it is a public place.)

What do you think? Have you seen this before?

Grasso, D. A., Sledge, M. F., LE Moli, F., Mori, A., and Turillazzi, S. 2005. Nest-area marking with faeces: a chemical
signature that allows colony-level recognition in seed harvesting ants (Hymenoptera, Formicidae). Insectes Sociaux 52:36–44. (.pdf available for viewing)