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On a recent trip to western New York State, we made a cool discovery.

Driving along a quiet country road, we came upon some huge ant mounds.

It's hard to tell how big they were until someone plays spokesmodel.

We found not just one mound, not just two mounds,

but more than twenty of them.

In the photo the size is a bit deceptive because the mounds were up on a bank along the road. However, they were still relatively massive. Most of them were at least two feet tall.

These impressive structures were the nests of the Allegheny mound ant, Formica exsectoides.

Each of the mounds was covered with many active ants. According to the literature, the colonies have multiple queens and split up via fission to form clumps of interconnected mounds.

The mounds are thought to help the ants regulate the temperature inside the nest, which in turn optimizes the development of the young.

Doing some comparisons, it looked like the top of each mound was clear of vegetation and the upper surface was relatively uniform.

This photograph shows a closer view of some ants working on top of the mound.

Lower down, the mound was covered with sparse vegetation and riddled with holes like a sponge. It would be fascinating to know whether these were for drainage, air circulation, or what.

Checking out the lower holes, we found they did serve as entrances and exits. One contained a myrmecophile, although it moved away so fast I couldn't tell if it was a beetle or roach nymph.

The ants were very active. It didn't take long to find a nearby foraging trail.


(This was filmed using a small endoscope attached to laptop, which required two people to run. I need to figure out a way to mount it on some sort of mobile tripod. Any suggestions?)

Compared to a similar-sized foraging trail of our Arizona Pogonomyrmex harvester ants, it was noticeable that these ants weren't carrying anything. Because they are known to feed on insects, as well as gather honeydew, they must process their food in the field. Anyone know more about their foraging behavior?

Even to people who aren't interested in ants, these mounds were such a presence that they inspired awe and curiosity. It would be great to get a chance to study them longer.

Have you ever encountered Allegheny mount ant nests?

This week we're going to be doing a little trash talking. About ant trash, that is.

midden-veterans-oasis-rugosus-nov-2012

Ant trash or "middens" are the discarded materials that ants pile around or near their nests or mounds. Today we're picking through the middens of a colony of Pogonomyrmex rugosus harvester ants found at Veteran's Oasis park in Chandler, AZ. This first photo was taken on November 29, 2012.

What do you see? Small bits of rocks, of course. Those are common around harvester ant nests.

Being familiar with the plants found in the area, it is also possible to pick out some discarded seed materials.

The fuzzy strips are from creosote bush seeds. (Links go to posts about the plant at Growing with Science blog.)

creosote-bush-seeds(Creosote bush seeds)

You can also find some desert mallow, Sphaeralcea sp.

desert-mallow-seeds

The desert mallow seeds have a covering that is often seen in these middens.

desert-mallow-actual-seedsThis is what the desert mallow seeds look like with the covering removed.

Finally, the larger pale seed toward the upper right is a mesquite of some sort.

rugosus-midden-may-2013-074The next two photographs were taken on May 6, 2013.

rugosus-midden-may-2013-close_0089

Taking a closer look, it is apparent that for the most part these middens consist of discarded dark gray fringed seeds from brittlebush, Encelia farinosa.

brittlebush-seedsBrittlebush seeds

 

rugosus-middens-august-029

In August 2014, although there were still brittlebush seeds, the mix was more varied.

rugosus-middens-august-27

The larger, ovoid brown seeds are apparently from a honey mesquite.

honey-mesquite-seedHoney mesquite seeds

 

p-rugosus-entrance-close-111

Over the weekend I visited the same colony again (April 26, 2015).

See the brittlebush and desert mallow seeds near the top of the photograph? Some of those were being dropped by workers from outside the nest and picked up by other workers to be taken inside. Other were being taken out.

rugosus-middens-spring-0074Around the nest, the ground is covered with plant material likely deposited by the ants.

rugosus-middens-spring-2015-0073Note:  the brown round objects are jackrabbit scats, probably incidental.

rugosus-middens-spring-2015-closeClose-up, it looks like quite a few desert mallow, creosote bush and some brittlebush discards.

What does studying middens tell us?

First of all, from the photographs we can safely say that as the colony has matured it seems to be gathering a substantially larger amount of plant material. The amount of middens probably isn't a clear indicator of colony size, however, because the quantity of middens likely also varies with season, habitat, and recent weather. Taber (1998) indicates that worker harvester ants may store trash in underground chambers. These trash chambers may be closed off, or periodically cleaned out and brought to the surface causing a flush of discarded materials.

We can also make some assumptions about what seeds the harvesters are gathering throughout the season.  Thus, these Pogonomyrmex rugosus workers are gathering seeds from mostly local desert species of plants.

What ends up in the trash, however, may not accurately entirely reflect what is being consumed. It is likely some seeds are used completely and have no husks to discard. Think about it, how accurately does your trash reflect what you eat?

Have you studied ant middens? What did you find out?