Tag Archives: harvester ant middens

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?

Remember that  Pogonomyrmex nest with the shiny black spots around the nest entrances from a few weeks back?

 

black-spots-another-view

This one?

Upon revisiting a few weeks later, the ants are looking better.

Pogos-previously-with-black-spots

They seem to have cleaned up nicely.

pogos-were-black-spotted-12

Maybe there are a few spots left, but nothing like before.

pogos-gathering-food

What are they harvesting today? You probably recognize the beetle elytra, but what is the gray cylinder?

pogos-with-screwbean-mesquite

You might need to be from Arizona to recognize it. That is part of a seed pod from a tree with the common name "screwbean mesquite."

Wonder what they will be up to next time I visit.

What kind of ants do you visit regularly?

While visiting a local park this week, I stopped by to visit a Pogonomyrmex nest I have been watching over the years.

black-spots-around-harvester-ant-nest

I almost immediately noticed the black spots around the nest entrances.

black-spots-around-harvester-ant-nest-another

Here's another entrance about 20 inches from the first two. There was a noticeable blackening around the hole in comparison to the surroundings. Otherwise, the ants seemed to be active and doing fine.

black-spots-another-view

This is a closer view.

black-spots-close-up

Looks kind of shiny.

My first thought was ant feces. Studies have shown that some ants mark their nest areas with feces, for example a study by Grasso et al. (2005).

black-spots-33

My other guess is that someone tried pouring something into the nest (as it is a public place.)

What do you think? Have you seen this before?

Grasso, D. A., Sledge, M. F., LE Moli, F., Mori, A., and Turillazzi, S. 2005. Nest-area marking with faeces: a chemical
signature that allows colony-level recognition in seed harvesting ants (Hymenoptera, Formicidae). Insectes Sociaux 52:36–44. (.pdf available for viewing)