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.