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Trachymyrmex septentrionalis: Nascent Leafcutter?

- by Joe MacGown

Similar to their leaf cutting relatives in the genus Atta, Trachymyrmex cut sections of leaves with their mandibles, which they then carry piece by piece to their nests, to use as a substrate to grow their fungus on. I recently (April 22, 2006) observed this interesting behavior in the front yard of a house owned by David Cross and Juliet Tang in Starkville, Oktibbeha County, Mississippi. The nest was seen at approximately 1:25 P.M. on a partly cloudy and warm day with the ambient temperature at about 85 F. Generally, I don't find this species to be overly active at this time of day, but the front yard where the nest was located was quite shady, which perhaps influenced the ants' activities and the temperature was not overly high yet. In a few more weeks, these ants will not likely be seen rambling so freely during midday. The yard was on a nice slope, which is not unusual for this species, and I have often found Trachymyrmex nesting on slopes. It was David, an avid naturalist himself, who actually first noticed the ants carrying bits of leaf material to their nest and cutting the leaf bits from the leaf with their mandibles. Despite the obvious bounty of otherwise green plants in the immediate vicinity, the workers seemed instead keen on only cutting pieces from a fallen leaf of a red oak tree (Fagus rubra L.). The leaf was about 20 to 25 cm away from the nest entrance. David speculated that the fallen leaf, being a somewhat new leaf, had less tannins than an older leaf would have, and possibly the ants preferred this. A good question for sure. The worker ants formed a weak column with seemingly random individuals carrying leaf bits back to the nest. Only about 1 out of every 4 ants appeared to be carrying leaf bits, while the other workers appeared to be returning without anything. One worker was seen to be carrying what appeared to be some type of insect feces. As workers were carrying material to their nest, Monomorium minimum (the little black ant) and Solenopsis invicta X richteri (the hybrid fire ant) were observed freely crawling about in the same area, occasionally crossing the Trachymyrmex column. However, at no time were the three species seen to interact with one another in any manner.

* Article originally from Mississippi Entomological Museum

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