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Did you know that today is International Rock Flipping Day?

The idea is to go outside, flip over a few rocks, and record what you see. The resulting posts will be published at Wanderin' Weeta.

After looking under a couple of rocks, I posted about most of the creatures I discovered (including a very cool case-bearing larvae) at Growing With Science. Of course flipping rocks is a fabulous way to find ants (and "experience" ants in other ways, too), so let's take a look at what ants were hiding under rocks today.

The area I chose has mowed grass with a brick edging around it, as well as some rocks piled up in a drainage ditch. It isn't uncommon to see Forelius running along the edging, so it was no surprise to find a few under the rocks as well.

Southern fire ants were in full force, too.

I was surprised how much more red these show that the ones in my yard a football field-length away.

I managed to get stung while taking this photograph. (Flipping rocks does has its hazards.)

Of course, Dolichoderinae don't sting.

But they are more than willing to bite.

At least it was sitting still, so it is in focus 🙂

Did you participate in International Rock Flipping Day? What did you find?

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Right on cue the Solenopsis xyloni have been swarming in Phoenix.

At eight in the morning, the new queens are climbing up grass stalks and leaves.

Any idea why the worker ants are standing on and huddled around the queens?

I'll give you a hint.

You might be able to spot two of the reasons near the center line in this blurry photograph.

I'm afraid this is the best shot I got of the aerial assault by phorid flies.

Phorid flies of the genus Pseudacteon are known to attack fire ants. They are commonly called ant-decapitating flies for the fact that the infested ant's head falls off during the final stages of the fly's development. Each fly lays her eggs into the adult ants. The fly larva hatches from the egg, and feeds within the ant’s alitrunk. Once the larva is ready to pupate, the ant dies and literally loses its head. The larva pupates in the cozy head, and eventually emerges as an adult fly to attack more fire ants.

Photograph from Wikimedia

There was a small cloud of the flies attracted to the activity of the ants. These phorids seemed to particularly target the reproductives, although other phorids I have read about target workers.

To give you an idea how small and fast these flies are, check the area around the beige leaf in the lower right corner of the second part of this video.

Have you ever seen phorid flies around swarming ants? If so, what species of ants?

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The first thing you notice about workers of the Southern fire ant, Solenopsis xyloni, is what fierce foragers they are.

You never see just one foraging worker. Instead, there's almost always a teeming mass.

Even when they are collecting sweets at extrafloral nectaries, Southern fire ants show up in greater numbers than most other species.

Southern fire ants are thought to be originally from throughout the southern and western United States. They have been displaced in many areas by the imported fire ant, Solenopsis invicta, but still occur widely in the dry areas of Arizona and California.

Identification:

Solenopsis ants are relatively easy to tell from other ants because of the antennae have ten segments with a two-segmented swollen area or  "club" at the end.

Solenopsis xyloni workers vary considerably in size and color, even within colonies. The larger workers tend to have lighter-colored heads and trunks than the smaller workers. In the area around Phoenix, Arizona, the Southern fire ants seem darker than those found elsewhere.

(These workers are feeding on their favorite meal of dried cat food.)

Where Solenopsis xyloni and S. invicta overlap it is difficult to distinguish the two species. Jacobson et. al. (2006) have developed a pcr technique and guidelines for identification (see references).

To make things even more confusing, it seems that Solenopsis xyloni hybridizes with Solenopsis geminata where the two overlap.  Obviously this group is "interesting" from a taxonomic standpoint.

Foraging:
The foraging workers are often seen carrying bits of hard food or arthropod parts back to the nest. They also gather some seeds.

Wet food, like this watermelon, go straight to the crop.

Often the foraging trails around their nests are underground or partially covered, so you might not notice them until you dig into the soil or pull up a weed. Then they come boiling up seemingly out of nowhere.

When foragers cross a man-made structure, such as a walking trail, sidewalk, or tile floor, they form a dense foraging trail of numerous workers traveling in both directions.

You have to admire the ability of Southern fire ants to find, process and transport food very rapidly. Plus they seem to eat just about anything they encounter. It is no wonder the colonies can grow to a relatively large size.

Do you have fire ants where you live? Have you ever watched them gather food?

References:

Solenopsis xyloni by Dale Ward

The Navajo Ant Project has a brief review of taxonomy

Ant Web shows some of the color variation within the species

Jacobson AL, Thompson DC, Murray L, Hanson SF. (2006). Establishing guidelines to improve identification of fire ants Solenopsis xyloni and Solenopsis invicta. J Econ Entomol. 99(2): 313-22.

Trager, J. C. (1991). A revision of the fire ants, Solenopsis geminata group (Hymenoptera: Formicidae, Myrmicinae).  Journal of the New York Entomological Society. 99 :141-198.