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A friend is building a new house and he wanted to know about the ant colonies he found in his yard.

Photograph by Bill Webster

These shiny black ants are Messor pergandei (also seen in the literature as Veromessor.) They are a type of harvester ant, which means they collect, process, and store seeds as their main food source (See previous post).

Nearby was another ant colony.

Photograph by Bill Webster

Although these ants look similar superficially to those above, on closer inspection their bodies are dark maroon-red rather than black, particularly in the mid section. They also have fine parallel grooves on their heads. Theses ants are harvesters known as Pogonomyrmex rugosus.

Although both these species harvest similar types of seeds, it is not uncommon to find them living near each other. Robert Johnson (1992) suggests that they may segregate over broad regions based on soil texture, but coexist together in regions of overlap.

Some of Bill's earlier photographs showed the ants had placed a ring of wood fragments from construction as a barrier around their colony. It would be interesting to see whether they were reacting to conspecific colonies or those of other species.

Wouldn't it be cool to have ant neighbors like these?

For more information:

Kwapich, C.L., Gadau, J. & Hölldobler, B. (2017) The ecological and genetic basis of annual worker production in the desert seed harvesting ant, Veromessor pergandei.
Behav Ecol Sociobiol 71: 110. https://doi.org/10.1007/s00265-017-2333-1 (link)

Johnson, R.A. (1992) Soil texture as an influence on the distribution of the desert seed-harvester ants Pogonomyrmex rugosus and Messor pergandei
Oecologia 89: 118. https://doi.org/10.1007/BF00319023 (link)

Johnson, Robert A. 1991. Learning, Memory, and Foraging Efficiency in Two Species of Desert Seed-Harvester Ants. Ecology 72: 1408- 1419. (link)

Rissing, S.W. (1988) Dietary similarity and foraging range of two seed-harvester ants during resource fluctuations. Oecologia 75: 362. https://doi.org/10.1007/BF00376938 (link)

Most of the time it doesn't look like much is going on in the Sonoran desert during the day.

desert-scene

Of course, looks are deceiving, because there is often a lot going on that is subtle.

After a rain like we had this weekend, however, life comes bursting out.

We went for a hike at South Mountain Park on Sunday morning. Rain had fallen in the night, and as you can tell from these photographs, it was still cloudy. It was also extremely humid.

messor-pergandei-mound-activity

 

It is impossible to capture the level of activity in photographs, but ants were just streaming out of their nests. These are shiny black Messor pergandei.

Rain stimulates activity for at least two reasons.

nest-messor-pergandei-good

First of all, the ants are scurrying to collect seeds.

messor-pergandei-carrying-seeds

Some desert plants release their seeds in response to rain. Also, the rain knocks down seeds that are higher up in trees and shrubs. That means there is a flush of new seeds to collect after a storm.

Most of you probably already know the second reason ants are hyper-active after a summer rain.

p-rugosus-princess-1.JPG

See if you can spot the reason in these photographs of a Pogonomyrmex rugosus nest entrance.

p-rugosus-princess-2.JPG p-rugosus-princess-3.JPG p-rugosus-princess-4.JPG p-rugosus-princess-5.JPG

 

Did you spot the princess (alate)?

She went back inside this time, but I bet later in the afternoon the alates from this nest were swarming.

Wish I had all day to watch them and a HD video camera. Maybe someday soon...

Are the ants swarming where you live?

 

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Over at my Growing with Science blog I have been doing a long-running series about insects called Bug of the Week, as well as a series about identifying seeds, called Seed of the Week.  "Ant of the Week" seems to be inevitable.  So, without further ado, our first Ant of the Week is Messor pergandei.

These sleek, black beauties are a type of harvester ant. The photographs were taken at South Mountain Park in Phoenix, Arizona.

As harvesters, Messor pergandei workers gather seeds from local plants. In their book, The Ants, Hölldobler and Wilson list it as relying primarily or exclusively on a diet of seeds. It is thought their seed storing behavior might be why they can withstand living in areas that are very dry or experience prolonged droughts.

Looking at the trash heap, or midden you can see the semi-circular rim of spines from a bur clover, Medicago sp, probably Medicago poymorpha. (See, Seed of the Week does come in handy :-)). Dale Ward reported Messor ants gathering creosote (Larrea) and gold poppy in similar habitats. Rissing found combseed, Pectocarya platycarpa, and 35 other species of plants in harvester ant middens.

Hölldobler and Wilson also suggest that the ant can survive in harsh desert conditions because of their flexible foraging strategies. Single workers search for seeds when food is in short supply and when a patch of suitable seeds is encountered, a large number of workers are recruited.

Foraging workers are known stridulate to recruit to seed sources. Ants of all castes in the genus Messor have the ability to stridulate, even the males.

Harvester ants like Messor do more than simply eat seeds, they also may help disperse them. Rissing (1986) found six species of plants were more likely to occur around harvester ant mounds, and two of those plants showed a 6 to 15 fold increase in fruits or seeds when they were growing near a nest versus away from a nest.

Messor pergandei has been receiving a lot of attention lately because scientists have discovered that in certain regions colonies have only one queen as a result of a single queen founding a colony, but in other areas multiple queens start a nest together and then fight one another until only one queen is left. In still other areas, colonies have multiple queens that cooperate (called primary polygyny). (Cahan, et. al., 2005). Sounds like some exciting avenues for further research.

This is just a brief summary of this fascinating species. For more information, try:

Dale Ward on Messor pergandei, including videos

Alex Wild has a fabulous photograph of a Euryopsis spider catching a Messor pergandei worker.

Cahan, S. Helms and Rissing, S. W. (2005). Variation in queen size across a behavioral transition zone in the ant Messor pergandei. Insectes Sociaux. 52(1): 84-88.

Donato A. Grasso,  Marco Priano,  Gianni Pavan,  Alessandra Mori,  Francesco Le Moli. 2000. Stridulation in four species of Messor ants (Hymenoptera, Formicidae). Italian Journal of Zoology, Volume 67, Issue 3: 281 – 283.

Steven W. Rissing. (1986). Indirect effects of granivory by harvester ants:  plant species composition and reproductive increase near ant nests. Oecologia. 68:231-234. (free .pdf)

Note:  In the older literature the genus name of this ant was Veromessor.