At first glance the workers look somewhat like Camponotus pennsylvanicuscarpenter ant workers. This worker is in the 6.5-7 mm range.
The surprise comes when an alate comes crawling out of a tunnel. At this scale you probably still can't see the difference.
That alate is much smaller than an alate of of a Camponotus pennsylvanicus.
Looking closely at a front on view of a worker's head, you find that they lack hairs on the genae and have few on the clypeus. These are Camponotus nearcticus workers.
I was a bit surprised, because in the area I was collecting I had typically encountered C. nearcticus with a brown-red mesosoma, like this one at BugGuide. Just goes to show, once again, that color is not a useful guide to identification in ants.
According to Hansen, this species is spread throughout the eastern United States and across the northern U.S and southern Canada all the way to the West Coast. They are even found in certain parts of Arizona, although not in the low desert.
The alates are apparently reared in the fall and overwinter in the nest, as with other carpenter ants. I did not find any larvae or other immatures.
Their biology seems to be similar to that of other carpenter ants, but they have not been studied extensively.
One of the first things you notice about the Formica fusca group ants are their mounds.
(These photographs were taken in the Colorado Rockies).
Bare mounds of soil and small pebbles stand out amongst the vegetation.
As you get closer, you can see that the mound does have some brown bits of vegetation scattered about, such as dried conifer needles. There are also multiple entrance holes, something you don't see as much in the mound-building harvester ants.
Closer still and you can see the black ants with their large eyes. These ants are called the "Formica fusca group" because there are a number of ant species that can be hard to distinguish from one another. (See the resources at the bottom for more information.) My best guess about these are that they are part of the Formica subsericea complex, possibly Formica podzolica,, although they look a bit small.
Formica fusca ants get their common name "wood ants" because they live in forested areas or woods, not necessarily because they live in wood. Wood ants, or thatching ants as they are sometimes also called, are easily confused with carpenter ants. Typically the Formica ants are smaller than Camponotus, and the back of their alitrunk (midsection) has a valley or depressed area, rather than evenly rounded like the carpenter ants.
Many species build their mounds in the cooler forests of North America, Europe and Asia. Some of the wood ants cover their mounds with pine needles and bits of twigs, so they look like they have thatched roofs, even more than we saw in the photograph above. The piled up homes catch the sunlight and create a warm interior that allows these ants to live in colder places than most types of ants.
Wood ants feed on aphid honeydew as well as scavenge dead arthropods. They are also predators of common forest pests and are considered to be beneficial to the forest.
Wood ants lack a stinger. They defend themselves by spraying droplets of formic acid when disturbed, which causes most enemies to retreat. They also can bite.
At a nearby mound I noticed an interesting behavior that may have been related to defense. The workers were wrestling with a green aspen leaf that had fallen on the mound.
As you can see, the workers are chewing on and biting off pieces of the leaf.
In this video, you can see the same behavior. At the same time, the ants are apparently leaving the brown twigs alone.
Do you think it is sanitation? If they wanted to get rid of the leaf, wouldn't they simply cart it to the side and dump it? Do you think they using the bits of leaves for something? Or perhaps the moister leaves are more likely to mold and cause sanitation issues than the drier twigs and needles.
In any case, ants of the Formica fusca group are fascinating ants.
Are you ready for ant season to begin? I sure am! We've been having some unusually cold and rainy weather, so the ants haven't been very active. One warmer afternoon last week, however, I did spot a few ants other than rover ants. They were Solenopsis amblychila workers. Solenopsis amblychila workers are pale, golden yellow. Solenopsis amblychila can tolerate dry conditions. Colonies of this species are found mostly in the Sonoran Desert, that is southern Arizona, southern California, northern Mexico and Baja California, although they do extend further east into Texas as well.
These workers are nesting at one of our local parks, along a sidewalk. The surrounding area is compacted, dry Bermuda grass trampled by thousands of feet. The attraction may be a Solenopsis xyloni colony about a foot away, or may be a nearby ramada full of messy, snacking children.
I found a queen last year, but it met with an accident (also child-related as it turns out) and never had a chance to produce eggs.
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.
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/