Here is Chandler, Arizona the temperatures the day this was taken ranged from a low of 45° F (7° C) to a high of 78° F (26° C). What are the ants doing here?

Any activity at this Pogonomyrex harvester ant nest?

Can you [...]]]> In the last post, I looked at carpenter ants overwintering in upstate New York.

Here is Chandler, Arizona the temperatures the day this was taken ranged from a low of 45° F (7° C) to a high of 78° F (26° C). What are the ants doing here?

Any activity at this Pogonomyrex harvester ant nest?

Can you see the ant coming out of the nest entrance?

Looks like a bit of housecleaning.

Most of the workers were coming out of the nest carrying debris.

The ants were moving about six to eight inches from the entrance and depositing.

What are ants doing where you live?

The temperatures were hovering around freezing in upstate New York, where I was helping someone spit firewood.

When the wood split, occasionally we would find tunnels, hardly more than grooves in the wood, packed with ants. Although the ants look like they [...]]]> Last week I got a peek at where Camponotus pennsylvanicus carpenter ants spend the winter.

The temperatures were hovering around freezing in upstate New York, where I was helping someone spit firewood.

When the wood split, occasionally we would find tunnels, hardly more than grooves in the wood, packed with ants. Although the ants look like they might have been moving, they were mostly stiff and inactive. You could shake them out onto the ground without much resistance.

This group was in softer wood with more decay. Notice the larva. Most of the clusters of worker ants had small larvae with them.

Camponotus carpenter ants that live in temperate climates enter a state of slowed metabolism, called “diapause”, in the late fall and through the cold parts of the winter. Generally, the queen stops laying eggs. The workers begin to aggregate more than before. The workers develop large fat bodies, which can be seen as their gasters swell in size, as well as produce glycerol. Glycerol is an alcohol that helps prevent the formation of ice crystals within the ants’ bodies. No wonder the ants stagger a bit when they try to move.

What are ants doing this month where you live?

For more information try:

Cannon, C. A. 1990. Demography, cold hardiness, and nutrient reserves of overwintering nests of the carpenter ant, Camponotus pennsylvanicus (De Geer). M. S. Thesis, Virginia Polytechnic Institute and State University. 165 pp.

Cannon, C.A. and R.D. Fell. 1992. Cold hardiness of the overwintering black carpenter ant. Physiol. Entomol. 17:121-126.

Check out this mound the ants had constructed.

Most of the workers I saw were carrying clumps of dirt/pebbles.

The worker dumped her load and then went back for more.

The surface of the mound looks like a boulder field from the perspective of the ant.

Harvester ants and [...]]]> The leafcutter ants were busy in Tucson a few weeks ago.

Check out this mound the ants had constructed.

Most of the workers I saw were carrying clumps of dirt/pebbles.

The worker dumped her load and then went back for more.

The surface of the mound looks like a boulder field from the perspective of the ant.

Harvester ants and other types ants also have pebbles on the surface of their mounds. (Harvester ants decorate their mounds with other things as well.)

A curious docent wondered why I was taking photographs of the ants. After wishing the mound was in the sun, she volunteered to show me another mound she knew of that she thought might be in the sunlight.

Turns out it wasn’t in the sun, but there was something else there.

You see those cords? A crew that was stringing Christmas lights had trampled the leafcutters’ mound. I’m not sure whether the ants simply reverted to another entrance or whether they abandoned the nest.

I was intrigued to see those circles though. Do you know what they are?

Those are pits made by larval antlions (See previous post about antlions.)

Antlions seem to prefer fine, powdery soil (The Antlion Pit).

So, do you think perhaps ants may decorate their mounds with pebbles in an effort to keep down antlions, as well as other species of ants as has been suggested? Do you know of anyone who has studied this possibility?

I examined the refuse piles, or middens, to see what the ants had been gathering.

Pogonomyrmex barbatus typically gather seeds and their middens reflect that.

The larger ovoid seeds caught my eye, because I knew [...]]]> On a recent trip to the Hassayampa River Preserve, we ran across a number of harvester ant mounds, particularly those of Pogonomyrmex barbatus.

I examined the refuse piles, or middens, to see what the ants had been gathering.

Pogonomyrmex barbatus typically gather seeds and their middens reflect that.

The larger ovoid seeds caught my eye, because I knew what those were from.

The Hassayampa preserve has numerous mesquite trees of various kinds.

The trees were covered with seed pods.

More mesquite pods covered the ground under the trees.

If you look closely, the pods consist of strings of seeds embedded in a starchy, sweet material that is sometimes ground up and used for flour. Having tried grinding up the pods before, I knew they are fairly tough.

Somehow the harvester ants were finding partially processed seeds with the starchy pod removed.

It seemed doubtful they were processing the pods themselves, at least I saw no evidence they were when I looked at the piles of pods under trees. Time to look around some more.

That’s when I found a big. smelly clue.

Ah, now that makes more sense.

My best guess is that the scat comes from a coyote. In the Sonoran Desert coyotes consume a lot of mesquite pods. Apparently they digest the pods but leave the seeds “behind.”

Have you ever seen harvester ants scavenging seeds from scat? Do you know what kind?

Take these harvester ants, for example.

Your eye might be attracted by the flurry of activity around the nest entrance.

It does pay to look elsewhere, though.

Here’s the trash heap. Looks like these ants have been gathering a lot of Isopods, otherwise known as [...]]]> You can tell a lot about a society by what its members throw away.

Take these harvester ants, for example.

Your eye might be attracted by the flurry of activity around the nest entrance.

It does pay to look elsewhere, though.

Here’s the trash heap. Looks like these ants have been gathering a lot of Isopods, otherwise known as rolypolies.

This midden was extensive, and strewn with Isopods.

As an entomologist, my eye was drawn to the beetle elytra (hard upper wings).

Here’s another beetle.

The harvester ant mound was along a trail at Boyce Thompson Arboretum near Superior, Arizona.

About 1/2 mile away, I spotted another mound of the same species.

This one seems to have more plant material, plus a bit of egg shell.

Still a lot of Isopods, although the exoskeletons are more broken up. There’s an elytra of the same kind of beetle as was on the first harvester ant mound.

There’s another elytra.

It felt good to get out and see some ants, although the time was much too brief. I would like to have looked around more thoroughly.

And, oh yes, there were a few flowers too.

Did you get to do any hiking this weekend?

One of the most common ways to keep ants is in a glass test tube nest. The advantages are that glass tubes are easy to clean, supply the proper moisture, convenient to transport and can grow [...]]]> I often get questions about raising ants. How do you keep a colony disease-free and growing in an artificial nest?

One of the most common ways to keep ants is in a glass test tube nest. The advantages are that glass tubes are easy to clean, supply the proper moisture, convenient to transport and can grow in number as the colony grows.

1. Obtain a glass or plastic test tube. The size depends on what kind of ants you are keeping. You can find test tubes at most scientific supply stores.

2. Fill roughly 1/3 way with water. Use clean, good quality water.

3. Roll up a sterile ball of cotton and shove down to the top of the water surface. The idea is to keep the water from flowing out, but create a humid chamber for the ants by creating a tight plug of cotton. Push the cotton down with a clean probe or skewer. See that the moisture does not come past the top of the cotton plug. If it does, pull out the plug and try again with fresh cotton.

You can set the test tube in a plastic bin rimmed with fluon, a milky teflon-like substance that keeps ants from crawling away (see below). Or you can start out by plugging the tube with cotton to keep the ants inside.

Once the number of workers increases, you can add more test tubes.

For more information try:

How to Make An Ant Farm

Instructions For Building Artificial Ant Nests

How to Feed Queen Ants

Where to Get Fluon

AntsCanada Ants Store

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 [...]]]> 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/

During the summer, we accidentally discovered several colonies when transferring potted plants, so we know they nest in those. We also watched a colony relocate from one nest in the soil to another. It was cool to see the big gush [...]]]> In an effort to learn more about rover ants, I have been searching for nests.

During the summer, we accidentally discovered several colonies when transferring potted plants, so we know they nest in those. We also watched a colony relocate from one nest in the soil to another. It was cool to see the big gush of ants along the trail as the queen and her entourage moved through.

This week I found another place where some rover ants are hanging out.

From a few feet back, it doesn’t look like much. This is an old stalk from a hollyhock. Hollyhock stems are filled with a soft, white pithy material.

It doesn’t look much more significant close up.

If you watch for a few minutes, however, it becomes apparent that some ants live here.

Note to self:  investigate that beige shiny stuff around the entrance. Any ideas?

This one seems to be eliminating something. I wonder if that has anything to do with the shiny material?

Most of these are fairly light-colored workers. It is also about 50 °F and shaded for the most part, so activity in the entire yard is way is way down. We’ll see what happens as it warms up again.

By the way, the shape of this entrance leads me to suspect it was once created by another insect.

This is the entrance of the small carpenter bee, Ceratina that I found nesting in the hollyhock stalks earlier. If the entrance above is one created by a carpenter bee, then the ants have closed it up a bit.

So, is this a nest or some sort of bivouac? What do you think?

At first glance a harvester ant mound looks a bit like a pile of rubble.

If you start to study the mound, [...]]]> Remember the post a few weeks back showing the snail shells in the harvester ant midden? Let’s take a little closer look at what kinds of objects harvester ants collect and put on their mounds.

At first glance a harvester ant mound looks a bit like a pile of rubble.

If you start to study the mound, however, you begin to notice that the pebbles are roughly the same size. Harvester ants (Genus Pogonomyrmex) are known to gather various objects and deposit them around their nest entrances. Harvester ants in the western United States often gather pebbles, among other things.

Fossils

if you are interested in harvester ants, you should pick up the fascinating article by Daniel Adams in Smithsonian Magazine from 1984.  Adams described how paleontologist John Hatcher discovered a terrific place to find tiny fossils, such as the teeth of mouse-sized mammals. In fact he went from finding an average of 2 per day to over 87 per day.  What was his secret? Hatcher discovered that harvester ants pick up ant-sized fossils and drop them on their mounds. Hatcher simply had the locate ant mounds and sort through the piles. Much of what is known about the mammals that lived during the time of dinosaurs is due to the diligent collecting behavior of harvester ants.

Paleontologists and archaeologists both still use mounds as a source of tiny fossils today. The University of Colorado Museum of Natural History has an exhibit honoring the contribution of the western harvester ant (Pogonomyrmex occidentalis), called Tiny Collectors: Harvester Ants. This page has a photograph of a mound and more information about how the fossils are collected.

Most of the finds are in Montana, the Dakotas, Wyoming, and Colorado. I’m not sure, but there might even be something in the mound from Arizona.

Can you spot it in the upper right hand corner? To me it looks a bit like a tooth.

Beads

In 2009, Schoville et al. distributed beads of various sizes and colors around harvester ant mounds at measured distances to investigate how far harvester ants move artificial material. They found ants would bring back beads from as far as 48 m away, but most were collected within 20 m of the main entrance. They were interested in how harvester ants moving artifacts potentially effects archaeological findings.

Charcoal

Deborah Gordon first studied deposits of charcoal in Pogonomyrmex badius middens in 1984. She established that the pieces of charcoal were not incidental, because if she removed the charcoal bits, the ants quickly began replacing them. She concluded that the charcoal probably marked the ants’ territories and deterred other ants.

Smith and Tschinkel re-visited what they called “non-food collection” by harvester ants. They evaluated mounds in Florida and found that pieces of charcoal were the most common objects, as Gordon had. They suggested that the objects reflect a significant amount of material, and that once again, the collecting behavior probably isn’t incidental. They found a slight increase in temperature in mounds with charcoal versus those without, but found no evidence other ant species avoided the pieces.

Snail Shells

It turns out that other people have also noticed snail shells on harvester ant mounds.

PÁLL-GERGELY and SÓLYMOS are malacologists working in Turkey who found that harvester ant mounds can be a significant source of taxonomic material, especially for more cryptic species of snails.

They noted that the ants tended to collect the smaller species of snails, and the juveniles of larger species. They did not observe the ants feeding on snails, but noticed some shells were cleaned out and some were not. They emphasized that harvest ants are known to collect and feed on seeds.

Some ants do eat snails. Mark Moffett has a photo of a Basiceros singularis worker feeding a tiny snail to its larvae. (You might have to scroll through a few photos to find it.) Do harvester ants do the same?

Conclusions:

The bottom line is that harvester ants have some interesting and unusual things on their mounds, and as of yet, we don’t have a very clear picture exactly why or how. In any case, we humans have found ways to use their activities to our benefit.

What unusual items have you found on a harvester ant mound?

References:

Adams, D.B. (1984). Fossil hunters best friend is an ant called pogo: paleontologists use insects to find
small bones. Smithsonian, 15: 99-104.

Gordon, D. M. (1984), The harvester ant (Pogonomyrmex badius) midden: refuse or boundary? Ecological Entomology, 9: 403–412.

PÁLL-GERGELY, B. and P. SÓLYMOS. (2009). Ants as shell collectors: notes on land snail shells found around ant nests. Malacologica Bohemoslovaca, 8:  14–18.

Schoville, B. J. Burris, L. E. and L. C. Todd. (2009).  Experimental Artifact Transport by Harvester Ants (Pogonomyrmex sp.): Implications for Patterns in the Archaeological Record Journal of Taphonomy, 7 (4):  285-303.

Smith C. R. and W. R. Tschinkel. (2005). Object Depots in the Genus Pogonomyrmex:  Exploring the “Who,” What, When, and Where. Journal of Insect Behavior, 18 (6):  859-879.

Smith C. R. and W. R. Tschinkel. (2007). The adaptive nature of non-food collection for the
Florida harvester ant, Pogonomyrmex badius. Ecological Entomology, 32:  105–112.

For example, here’s the trash heap or midden of a Pogonomyrmex colony.

Shell collection?

Water condensation devices?

Taste for escargot?

Garlic and butter anyone?