April 2011 Archives

Dear Ant Experts,

We encountered a harvester ant mound during a recent hike for volunteer naturalists. We were discussing why the ants cover their mounds with small stones. One article I found says that they do this so the sun will warm the nest more quickly and radiate heat for the nest during the night. Do harvester ants bring stones out of a nest early in the day, place them in the sun for warming, then bring them back in for the night as a solar heat-source?

Also, do they "plug" the nest with a stone each night?


Dear Bob,

It is a really good question of why some ant species collect and deposit small stones around their nest entrances. Scientists have been addressing these questions, but it still remains unclear. We have contacted Robert Johnson who studies harvester ants and here is what he has to say:

"A number of harvester ants collect pebbles and bring them back to the nest, meaning that they intentionally retrieve these object - they are not excavated from inside the nest. The reason for this behavior is poorly understood, but there is a paper attached that discusses these ideas and why they might do it."

Chris R. Smith and Walter Tschinkel have published some papers, in which they investigated the question you asked and here is a link to the website with links to the pdf flies. The following publications might be of particular interest:

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

Smith, C. R., and W. R. Tschinkel. 2005. Object depots in the genus Pogonomyrmex: exploring the "who", what, when, and where. J. Insect Behav. 18: 859-879.

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

All the best,
Robert Johnson (guest expert), Steffi Kautz & the AntAsk Team

Dear Ant Blog,

We have an in-ground pool with a concrete deck. Over the years, cracks have appeared as expected from expansion and contraction. Unexpectedly, ants have started coming in through these cracks. At one crack, there is a swarm of little black/dark brown ants who come out, sometimes holding little white objects, and throw themselves into the water. There they form into large clumps, about the size of a Ping-Pong ball, and float around. We have also noticed larger ants that we think are guard ants. We tried to take photos, but the camera kept focusing on the bottom of the pool instead of on the ants. One theory we had was that this might be a way of starting a new colony. Just float off with some eggs and guards and start up where you land. Also, when we scooped one clump out with the skimmer, it promptly dispersed and the ants began swarming towards the hand holding it. This hasn't happened before, and we have been here for several years. Do you have any explanation?
The Lawtons

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Dear Lawtons,

Thanks for your interesting question and observation. We have deferred to colleague that happens to have quite a lot of experience with ants in the Gainesville area and with Solenopsis invicta, the Red Imported Fire Ant (which is what you are finding in your pool). Here is what Lloyd Davis had to say:

"The ants appear to be the Red Imported Fire Ant, Solenopsis invicta.  This species was introduced into the Southeastern US sometime between 1930 and 1950.  It came from South America, probably near Argentina or Brazil.  In its native habitat, the area surrounding a nest may be subject to unpredictable flooding.  These ants will cling to one another when flooded out of the nest or if they are trailing and fall into water.  I can't tell you why they ended up in your pool.  It is possible they were attempting to get to some other kind of insect that had also fallen into the pool."

You can read more about fire ants here, here, and here.

In addition there is a great video about this behavior of fire ants from the BBC, which can be watched here.

Thank you for contacting us,
Lloyd Davis (guest expert), Corrie Moreau & the AntAsk Team

What species of ant is this? It's a large species of ant that ive only seen a handful of times where i live in southern california. Theres a berry from a juniper next to the ant which makes it a little easier to understand how big it is.

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Dear Anthony,

Thank you for contacting AntBlog. Since you live in California, we asked Dr. Phil Ward, who is the curator for the AntWeb California Ants page to identify your ant. Here is what he had to say:


"This is an ant in the genus Camponotus, possibly Camponotus sansabeanus or C. semitestaceus (both common species in the drier parts of southern California). This individual is a dealate (or de-winged) queen. It is likely that she recently engaged in a mating flight, after which she dispersed some distance, landed on the ground, and discarded her wings. Unencumbered by wings she would now be searching for a nest site--under a stone or log, or directly in the soil--to start a new colony.

This method of independent colony foundation by a single queen is common in ants (you can read more about this here). In the case of Camponotus the queen sequesters herself in a cavity and begins to lay eggs. When these eggs hatch the queen feeds the larvae with regurgitated liquid food derived from the breakdown of her flight muscles. The larvae develop on this rather meager diet, eventually pupating and finally emerging as tiny adult workers, who open up the nest and begin to forage for food externally. Now the colony starts to acquire food resources from outside the nest cavity and it has the potential to grow rapidly. If it is successful (many incipient colonies fail) then in several years the colony will reach sufficient size to produce new sexual forms (queens and males) and the cycle continues."


You can also read several related posts here, here, and here.

Phil Ward (guest expert), Corrie Moreau, & the AntAsk Team