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A few ant nests dot the sides of a walking pathway at a nearby park, so of course I have to check them out.

For the most part the nests are small colonies of southern fire ants, Solenopsis xyloni.

There are also seemingly endless streams of Forelius mccooki workers traveling along the concrete edgers and sidewalks.

While taking photographs of the fire ant middens, I noticed the fire ants had a few visitors standing by an entrance hole.

Millimeters away from the fire ant workers stood two Forelius workers.

 

Curious, I watched for some minutes. The fire ants did not approach the Forelius, and the Forelius remained relatively still. They didn't appear to be investigating the middens.

The Forelius had a nest entrance not too far away. Perhaps they were just nosy neighbors? (I did notice there weren't any Solenopsis visiting them.)

Wayne Armstrong suggests perhaps the relationship isn't entirely benign. In this video, Solenopsis xyloni workers flag their gasters in response to Forelius pruinosus workers encountered at an artificial feeding site. (You will notice the coloration difference between our local S. xyloni compared to his California ones.)

Interestingly, the soldiers don't seem to respond. According to his notes (scroll down to Southern fire ant), the Forelius were ultimately successful in overtaking the food.

Ants of the Southwest has a photograph of a Forelius worker spraying a S. xyloni worker. He reports S. xyloni exoskeletons piled in Forelius middens, which is also reported here.

Even though southern fire ants are chemically well defended, perhaps they are no match for Forelius.

Have you ever encountered these two species?

References:

Obin, Martin & Vander Meer, Robert. (1985). Gaster flagging by fire ants (Solenopsis spp.): Functional significance of venom dispersal behavior. Journal of chemical ecology. 11. 1757-68. 10.1007/BF01012125.

What do you think is going on here?

forelius-on-desert-willow-group9

These are Forelius ants visiting the flower buds of a common landscape tree in the Southwest, the desert willow, Chilopsis linearis.

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Desert willows are not really willows at all, but belong the plant family Bignoniaceae, making them relatives of catalpa trees.

The trees have large, tubular flowers that attract hummingbirds and bees. Some varieties have dark magenta flowers,

desert-willow-flowers-2

whereas others have delicate, light pink flowers.

Forelius

Forelius are heat-loving desert ants. Many of the Forelius in this area are Forelius mcccooki (key to US species). They nest in the ground, but commonly forage on plants where they are known to gather sweet fluids from nectaries.

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Which leads us back to the question:  what are these Forelius workers doing on the desert willow flower buds?

Desert-willow-leaf-054

Both catalpa and desert willow are known to have extrafloral nectaries on the leaves. (Rico-Gray and Oliveira in 2007 defined extrafloral nectaries as sugar-producing glands found on the leaves, stems or stipules of plants.)

extra-floral-nectaries-desert-willow_0160Here are some buds from a desert willow tree that lacked ants. See the green spots?

desert-willow-buds

Do you think the light green structures (circled) are possibly what Rico-Gray and Oliveira define as circumfloral nectaries, that is nectaries around flower structures that are not attracting pollinators?

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Interestingly, a number of the flower buds on the tree without ants showed damage. What do you think caused this damage?

Looking into the literature, Ness (2003) found Forelius pruinosus workers attacked Ceratomia catalpae caterpillars on catalpa trees after visiting extrafloral nectaries. Ness also showed that leaf damage increased the sugar flow of nectaries within 36 hours. This supports the classic idea that plants attract ants to help fend off herbivores.

On desert willow, however, things might be even more complicated. Carey, Visscher, and Heraty (2012) found that an Eucharitid parasitoid of ants, Orasema simulatrix, laid its eggs in the extrafloral nectaries of desert willows, where the planidia had access to big-headed ant workers feeding there. The article has some fabulous photographs of extrafloral nectaries, by the way.

So, do you think the Forelius were visiting circumfloral nectaries? Have you seen any other ants visiting similar plants?

What do you think of Rico-Gray and Oliveira's separation of exrafloral nectaries from circumfloral nectaries? Is there a clear need to make a distinction? Would circumfloral nectaries have more likelihood to contribute to successful seed production than extrafloral nectaries?

References:

Carey B., K. Visscher, and J. Heraty. (2012) Nectary use for gaining access to an ant host by the parasitoid Orasema simulatrix (Hymenoptera, Eucharitidae). Journal of Hymenoptera Research. 27: 47-65. (Retrieved online)

Ness, J. H. (2003) Contrasting exotic Solenopsis invicta and native Forelius pruinosus ants as mutualists with Catalpa bignonioides, a native plant. Ecological Entomology. 28 (2): 247–251. (Retrieved online as .pdf)

The Ecology and Evolution of Ant-Plant Interactions (Interspecific Interactions) by Victor Rico-Gray and Paulo S. Oliveira, particularly pages 115 - 123.

Paperback: 320 pages
Publisher: University Of Chicago Press; 1 edition (July 15, 2007)
ISBN-10: 0226713482
ISBN-13: 978-0226713489

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I was going to take a photograph of a desert willow flower for another of my blogs, when I noticed some ant activity.

Forelius worker ants were all over one cluster of flowers.

As far as I could tell, they were only visiting this one cluster out of probably fifty nearby.

It would have been interesting to find out more, but I had to run (story of my life).

I have seen Forelius streaming up and down trees. They seem to forage in crowds.

What do you think?