Army ants eat Georgia Strumigenys

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Field Notes on Strumigenys — SCNC Artificial nest site 59-1 — Athens, GA Sandy Creek Nature Center — 10:00 am, 26 August 2012

On June 4 through 6, I placed four grids of 50 artificial ant nests inside a half-acre area of mixed pine and hardwood forest. On 26 August 2012, while Dr. Rick Duffield and I collected artificial nests, we found a trail of raiding Neivamyrmex opacithorax. When we cleared the leaves to determine their trail direction, we found a brood stash and discovered the trail forked and led to two artificial nests. While Rick was sucking up brood stash with his aspirator, I continued to follow their trail and collect a few workers.  The trail petered out as ants dispersed away from the trunk trail, but we managed to find another stash 30cm away from the first.  We had great success with the artificial nests at this site ,with colony recruitment to artificial nests near 20%.  Of 200 total traps, we collected 38 colonies including a second S. ohioensis colony (59-4-C9) and nine S. rostrata colonies. Though, it was our first artificial nest capture of Strumigenys in GA, we found the N. opacithorax activity most exciting.  Back at my microscope, I sorted the two N. opacithorax brood stashes as well as the ants we collected in the artificial nests.  The following tables quantify our observations.

Table1. Neivamyrmex opacithorax brood stash

artificial nest

pupae

larvae

refuse

 distance to brood stash

Strumigenys ohioensis

59-1-A4

14

15

y

2.3

Aphaenogaster carolinensis

59-1-A6

10

0

n

0.3

Temnothorax curvispinosus

59-1-B7

2

0

n

0.3

Nylanderia faisonensis

59-1-E4

2

0

y

1.3

Lasius alienus

n/a

0

0

y

n/a

Table 2. S. ohioensis colonies collected in artificial nests

artificial nest

distance  to brood stash

pupae

larvae

workers

gynes

S. ohioensis

59-1-A4

2.3

0

7

9

0

S. ohioensis

59-4-C9

45

18

23

43

4

 

We also found a lone S. ohioensis on a rock about a meter away from her probable nest (59-1-A4).  I wondered if N. opacithorax removed members of S. ohioensis colonies away from their nests along with brood, or if the ant was lost, foraging, or relocating/searching for a new nest?  I cannot imagine the slow moving Dacetine finding her way back home if the army ant dropped her even .5 meters from her colonies odor trails.

Previous witnessing this event, I likened Strumigenys’ spongiform tissue to the magic of an invisible cloak, manufacturing innumerate chemicals for protection, defense, predation, and possibly just making them plain invisible.  I still do not know whether the spongiform tissue produces chemicals or has other functions, but at least I reluctantly know S. ohioensis are part of N. opacithorax diet.  Just to check whether another Strumigenys may also fall prey to army ants, I brought home a live colony of Strumigenys rostrata as well as 20 army ant workers, but failed to recreate an environment producing natural N. opacithorax activity, and thus, there was no drama to report from home.

Dr. Richard M. Duffield is a Professor Emeritus of Howard University and was once a student of the fantastic chemical ecologist Dr. Murray Blum.  Rick has a nose for ants and can identify chemical compounds in, and thus many species of, ants by smell.  He recently published a paper on nut nesting and artificial nest use in Strumigenys and we have been working on improving and testing new artificial nest designs.

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