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.
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.
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.
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.
In addition to more isopod exoskeletons, other piles had seed husks, beetle elytra and a few feathers.
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.
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