Ask an Ant Expert: March 2011 Archives



Dear AntAsk,

I am growing Rubiaceous ant-plants (Myrmecodias and Hydnophytums) in a greenhouse in Michigan. The ants in the 3 photos attached here have moved into some of the Myremcodia plants.

The ants are 2 mm long. The are a reddish-tan color except for a black abdomen, black eyes and black clubs on the end of the antenna.

The photos are not too good. The lines in the photos are mm lines on a ruler

Thanks for your help.

Frank

Dear Frank,

Thanks for the question! Luckily, this genus of ants, Cardiocondyla, have some very distinctive characteristics, especially when top and side views are available. The post-petiole (the second segment of the "waist" of an ant) is always much wider and at least a little shorter and more shallow than the petiole (first segment of the "waist"). This character alone is usually enough to identify them. Another feature every member of this genus that I am aware of shares is the matte texture of the head and much of the thorax (for myrmecologists using a microscope: the dorsal surface of the head, petiole, post-petiole, and often much of the dorsal and lateral alitrunk is pocked with evenly spaced, shallow fovea, yielding what appears to be a fine punctate sculpturing under low magnification). As a general rule, one should not use texture as a character to identify ant genera, but I know of no Cardiocondyla that are smooth-headed, or have groves or wavy lines like some ants (compare an average Cardiocondyla with a Tetramorium or Diacamma).

With regards to the species, one of the most common and widespread species is Cardiocondyla emeryi. This species has been reported from many latitudes on every continent and many tropical islands around the world. A very nice representation of some of these localities is given on its species page on AntWeb (linked above). Another common, widespread species is Cardiocondyla obscurior.

More information on Cardiocondyla and its species can be found in Seifert's very thorough revision from 2003 ( linked here). As Seifert notes, the genus has many species that cannot be easily distinguished with a microscope, and C. emeryi itself has such a wide range and is so variable that many would not be surprised if it turned out to actually be multiple species. Because there seems to be almost as much variation within some of these species as there is between them (I think no one could have done a better job with this group than Seifert, but it does make me a little bit suspicious that he had to use mathematical formulae to make sense of his morphological measurements...), the last word may not have been written about the species limits even of the most familiar members of this genus. I encourage you to read more about the fascinating behavior and reproductive strategies of these ants (an excellent overview in the introduction of the Seifert 2003 article linked above). Perhaps we'll have to do another blog post some day on the fascinating biology of Cardiocondyla!

I hope this helps!
Best,
Jesse Czekanski-Moir & the AntAsk Team

What is the geographic range of leaf cutter ants (Atta spp) in the United States? Are there any known colonies of these (or other) fungus growing ants north of the Gulf States (in the Eastern US)?


Dear Don,

You may be surprised to know that leaf-cutter ants can be found in the United States! Although mostly a Neotropical group, both true leaf-cutters and the other fungus-growing attine ants can be found from South American through North America. There are ~230 described species of attine (fungus-growing) ants. In fact, attine ants are the world's first farmers and have been growing their fungal food crops for around 50 million years.

Here are the geographic distributions of the two true leaf-cutter ant genera (Atta and Acromyrmex) from the Ant Genera of the World website:

Atta_distribution.jpg

Geographic distribution of the leaf-cutter ant genus Atta. Image from Ant Genera of the World (http://www.antmacroecology.org/ant_genera; Guénard, B., M.D. Weiser, and R.R. Dunn. 2010).

Acromyrmex_distribution.jpg

Geographic distribution of the leaf-cutter ant genus Acromyrmex. Image from Ant Genera of the World (http://www.antmacroecology.org/ant_genera; Guénard, B., M.D. Weiser, and R.R. Dunn. 2010).


Recent work by Ted Schultz and Sean Brady has greatly contributed to our understanding the evolutionary history and timing of fungus-growing and leaf-cutting in the Attini ants [Ted R. Schultz & Sean G. Brady (2008) "Major evolutionary transitions in ant agriculture" PNAS 105 (14): 5435-5440.] You can read a nice review of the findings of this study on Myrmecos Blog here.

If you are interested in the geographic distributions of ants, I highly recommend checking out the Ant Genera of the World website.

Best regards,
Corrie Moreau & the AntAsk Team

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