A friend sent me this photograph of an ants' nest in a sidewalk.
What do you think they're trying to say?
This week we're going to be doing a little trash talking. About ant trash, that is.
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.)
You can also find some desert mallow, Sphaeralcea sp.
The desert mallow seeds have a covering that is often seen in these middens.
Finally, the larger pale seed toward the upper right is a mesquite of some sort.
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.
In August 2014, although there were still brittlebush seeds, the mix was more varied.
The larger, ovoid brown seeds are apparently from a honey mesquite.
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.
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?
Have you ever seen ants carrying or dragging bird feathers?
Sometimes they even carry feathers that are much larger than themselves.
It also not unusual to see feathers on or in ant nests. See, for example, this cool photograph of a Pheidole oxyops nest with feathers from Flickr.
Seeing these made me curious. Why do ants collect feathers? Why do feathers end up around their nests?
It is very likely that different ant species may collect feathers for different reasons. A quick search of the Internet and books about ants offer some plausible suggestions.
1. To Obtain Moisture
Mark Moffett found Diacamma rugosum ants in India decorate their nests with feathers during the dry season. The feathers collect dew drops in the early mornings, which the ants can then drink and share with nestmates.
He also proposes that the dead ants spread around outside the nest might also serve for dew collection.
(Moffett, M.W., Adventures Among Ants, page 119 and Moffett, M.W. 1985. An Indian ant's novel method for obtaining water. National Geographic Research 1 (1), 146-149.)
2. To Obtain Food
James Trager rightly suggests on the Ant Blog that foraging workers carry feathers home because they (the feathers) may have small residues of bird tissue or fluids that the ants eat.
Here are some Solenopsis xyloni workers stripping the remaining dried tissues from a clump of wing feathers of a dead bird.
3. Anting by Birds Leaves Feathers Behind
Another likely explanation for bird feathers around ant nests is that birds have been known to flop on ant nests or even pick ants up and rub the ants on their feathers. This behavior is known as "anting." It is thought that birds interact with ants, at least in part, to remove parasitic lice, ticks and and possibly microbes. It is likely that anting birds might leave feathers behind on the nests, particularly if the birds are molting.
This brings us back to the possibility of the ants collecting feathers for food, because at least some feathers may still harbor lice, mites, or small ticks if they fell off the bird recently.
I have witnessed Forelius ants pulling a feather into a nest entrance myself, but it doesn't seem very clear how frequently ants collect feathers. It might be a relatively rare phenomenon or it might be fairly common.
Have you ever seen ants collecting feathers? What about ant nest "decorated" with feathers? What do you think about it?