minigunl5 的鑑定

Atta texana nest of a population at the eastern range limit of this species in Evangeline Parish, Louisiana. Sandy soil. Mounds of Atta texana in this population are very large/old, and a retired local resident told me that texana colonies were abundant in the area as far back as the resident could remember. This is another population of Atta texana that is thriving at the range limit, like populations that I know in northern Louisiana and northern Texas.

I believe this is the first report of Atta texana for Evangeline Parish. I post this observation to help define the range limits of Atta texana.

observation UGM201105-04
elevation 39 meter

Large town-type mound of Atta texana, measuring about 51 meter X 22 meter. This is a single texana super-colony, with presumably many queens.

In Louisiana, such expansive mounds are called "ant towns", and Atta texana is therefore known as the "town ant" in Louisiana. I know of a few areas in Texas where similar texana towns occur, but texana towns seem to occur more frequently in Louisiana, and the Louisiana towns are clearly larger than those that I have seen in Texas. Not everything in Texas is bigger.

The area covered by this single texana mound is about 900 square meters (assuming the area of an ellipse 51m X 22m) with an estimated circumference of about 120 meter of the mound. This is about 0.22 acre (≈0.1 hectare) for this single texana mound. From this central mound, the ants likely built underground tunnels radiating out 80-150 meters in all direction, and from the remote exits of these tunnels the ants constructed above-ground foraging trails extending an additional 50-150 meter. So the entire foraging territory of this single ant colony could be well over 50000 square meters = 5 hectares (over 12 acres; area of about 9 football fields, or about 5 soccer fields), perhaps much more.

I estimate that this ant colony is at least 20 years old, perhaps much older.

Although the total area of heavily excavated soil of this single texana colony measured 51 meter X 22 meter, there appeared to be a newer part of the mound (first photo) where the ants had recently excavated much soil, and an older part of the mound (second photo), where the excavated soil was more washed-out by rains and there was less fresh excavate. This could indicate that this colony had expanded its mound into one direction, but not radially in all directions. Such a polarity of Atta mounds, and a shift in one direction as a colony grows (the workers are adding gardens primarily to one area of the mound, expanding the mound in one direction), was also reported by Autuori for Atta sexdens in Brazil.

The mound was at the edge of a clear-cut pine forest, along a road. In forested areas of Louisiana and Texas, I find mature texana colonies primarily at such forest edges, such as in clearings in the forest or along roadsides, and very rarely in closed-canopy dense mature forest. I believe that larger texana colonies migrate to forest edges, such that part of each mound is shaded (for soil moisture?), part of the mound exposed to sun (for warmth in winter?) and to provide unobstructed flight avenues when releasing winged reproductives (alates) during the mating flights in spring.

observation UGM201117-03
elevation 86 meter

Note added 03. April 2021: I posted another observation of a town-type mound of Atta texana from a location nearby: https://www.inaturalist.org/observations/72841374