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Dorymyrmex bicolor ants are common in Arizona, especially in open areas. In a previous post, I wrote about how to identify them.

A few weeks ago I visited an agricultural research station and found almost a monoculture of Dorymyrmex.

The first thing you notice about Dorymyrmex bicolor colonies is their neat circular mounds. (Most of these were conveniently located along the dirt roads.)

Each reflect the color of the soil beneath the surface. This one wasn't a perfect circle.

Nor this one.

Tofilski and Ratnieks (2005) studied the mound formation of two colonies of Brazilian Dorymyrmex. They found the worker ants removing excavated material from the nest deposited their loads at the crest of the mound and beyond, preventing the material from rolling back into the entrance hole. They also indicated that workers maintained the circular shape, when one side was removed, by climbing the area with the least slope to deposit their loads.

Ratnieks noted that ants of other, larger species had difficulty climbing the mounds, thus suggesting the mounds served a protective function.

As you will see in the next few photographs, the Dorymyrmex were carrying out clumps of soil and related materials the morning I visited.

Because ants at all the mounds were so busy removing material, I began to wonder about it. Were the clods of soil and pebbles rolling into the entrance hole over night? Perhaps there had been a wind storm or vehicle disturbance?

By the way, you might recognize these ants under a different name. Prior to a revision of the genera, Dorymyrmex bicolor was known as Conomyrma bicolor. Under that name, they had a brief burst of limelight when Möglich and  Alpert (1979) found they exhibited tool use by dropping small stones on their competitors, particularly Myrmecocystus workers. Finding ants that stoned their enemies caused quite a stir, as you can imagine.

Thinking about that, I also began to wonder if perhaps Dorymyrmex worker ants also use stone dropping on conspecifics. With the name change, it is somewhat hard to track the literature. Does anyone know?

If not, perhaps it would be worthwhile to visit these fascinating ants some evening.

References:

Adam Tofilski and Francis L. W. Ratnieks. (2005). Sand Pile Formation in Dorymyrmex Ants. Journal of Insect Behavior, 18(4): 505-512.
.pdf will load immediately at http://www.cyf-kr.edu.pl/~rotofils/tofilski_ratnieks_2005.pdf

Michael H. J. Möglich and Gary D. Alpert (1979). Stone Dropping by Conomyrma bicolor (Hymenoptera: Formicidae): A New Technique of Interference Competition. Behavioral Ecology and Sociobiology, 6 (2):  105-113.
free .pdf available at Springer
http://www.springerlink.com/content/p16717229406004l/

A few months ago I put up a post asking people to guess which states I had visited this summer based on the species names of the ants in the photographs.

If you had guessed Pennsylvania for this one, you would have been correct. Camponotus pennsylanicus colonies are found in a number of states throughout the East and Midwest, as well as Pennsylvania (Hansen and Klotz, p. 86). The ants in the photograph are in upstate New York.

Colonies of these ants are often found in wooded regions and Camponotus pennsylvanicus workers are commonly called black carpenter ants because of their habit of making nests in wood, such as stumps or rotting logs.

How do you tell a Camponotus pennsylvanicus worker from this Formica worker? Two characteristics that are relatively east to spot are the long blonde pubescence (hairs) on the gaster (rear section) of the Camponotus. The trunk (middle section) is evenly rounded when seen from the side for Camponotus, whereas there is a notch or valley in the Formica.

How do colonies start? The alates fly in the spring, usually on the day of the first spring thunderstorm. After mating, the queen pulls off her wings (you can see the wing scars on the side of her trunk) and starts her own nest, often under the bark of a fallen log like this one.

The males look more like wasps. The males die after the mating swarm.

The workers are polymorphic, ranging from 6-13 mm in length. Although the largest workers are sometimes called soldiers, they do much more than defend the nest. They also are involved in nest construction and foraging.

Carpenter ants do not have a stinger, but can bite to defend themselves.

The tasty red fruit is a mulberry. Camponotus workers often gather sweets from fruit, nectaries, extrafloral nectaries, and honeydew from other insects.

They also prey on or scavenge a number of different arthropods. For example, a recent study has shown Camponotus pennsylvanicus to be a predator of the red oak borer, Enaphalodes rufulus, a cerambycid beetle that was associated with oak decline in the Ozarks (Muilenburg et. al., 2008). Unlike harvester ants, Camponotus workers carry virtually all the food back to the nest internally (Cannon and Fell, 2002).

I wonder if they are going to find that caterpillar at the base of the bud.

Due to their large size,  carpenter ants are much easier to see and study than rover ants!

References:

Cannon, Colleen A. and  Fell, Richard D. (2002). Patterns of Macronutrient Collection in the Black Carpenter Ant, Camponotus pennsylvanicus (De Geer) (Hymenoptera: Formicidae). Environmental Entomology. 31( 6):  977-981.

Muilenburg, Vanessa L., Goggin, Fiona L., Hebert, Stephanie L., Jia, Lingling and Stephen, Fred M. (2008). Ant predation on red oak borer confirmed by field observation and molecular gut-content analysis. Agricultural and Forest Entomology, 10(3): 205-213.

Hansen, Laurel D. and John H. Klotz. (2005). Carpenter Ants of the United States and Canada. Comstock Publishing Associates, Ithaca.

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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.