The pains and pleasure of Bornean fieldwork
or "If the ants don't get you the plants will"
by
Steven Cook

email: cook@biology.utah.edu

     Dr. Dinah Davidson and I spent nearly 10 weeks last summer studying the dietary specializations and feeding performances of numerous ant taxa in the forests of the Temborong District of Brunei Darussalam. In effort to accomplish all that we wished to do, we were typically in the field all day, often standing for hours on end in circumscribed areas of sharply angled terrain. The working conditions proved to aggravate a callous on the bottom of my left foot, and it has since raged out of control, forming a red swollen pulsating protuberance. Traipsing through sometimes-thick understory vegetation, we were exposed to "attacks" by various plants that seemed far more vicious than the stinging Diacamma that reside here. The thought of climbing rattans, with serrate edges on their reaching rachi, still makes my skin ache. Another particularly unforgiving plant species, not yet positively identified, but most likely a member of the genus Gluta (Anacardiaceae), resembled a 30 meter tall poison ivy plant. Via rain and homopteran exudates, we were continually infected by these unseen enemies above and only recovered completely after returning home.
      Despite these trials, the stationary nature of our work provided an opportunity to see the ant fauna at a level of intimacy that would not have been afforded by simply walking through the forest, even at a pace slowed by the steep terrain. The long hours of fieldwork opened our eyes to intricate associations among ant taxa, to relationships between ants and other arthropods, and to the immense diversity of ant taxa in the area. Particularly interesting in reference to associations of ants with other arthropods, was the large variety of ant-mimicking spiders. On one occasion, Dinah spent almost an hour performing a behavioral assay on a presumably lichen-foraging ant species, only to find out that this "ant" was actually an apparently lichencolous spider. Only after this "Polyrhachis" let itself down from a leaf on a strand of silk was the true identity of the subject revealed.
      The magnitude of ant diversity at Kuala Belalong increased the more closely we observed ant behaviors in our feeding trials. A case in point is our discovery of a new species of a large-bodied Polyrhachis in the Myrma subgenus. At first glance, one might have mistaken this species for one or both of two coexisting species: Polyrhachis armata or a species of Polyrhachis in the Myrmhopla group. With black head and thorax, and sienna-rust gaster, both of these ants resemble the new species in coloration as well as size.
      The presence of this new species, "eventually to be described by Kohout" in a highly public venue makes the undescribed status of this species all the more surprising.       The type colony was collected (with alate females) along the quite open area lining the boardwalk to the canopy tower in the Temborong National Park. (We later found it deeper into the forest as well.) Perhaps more interesting is the nesting habit of this species. Several terrestrial "nest sites" (more likely one nest and numerous terrestrial pavilions) in close proximity appeared to belong to a single colony, whose workers interact without aggression. A central nest, from which brood was isolated, was located at the base of a vicious (see above) spiny palm, making it difficult to dig it up. Nevertheless, this nest cavity seemed to be highly structured, with distinct chambers accommodating brood and/or workers, not too far from the surface. At the surrounding sites, deemed to be pavilions, rather than nests, due in part to their simplicity and lack of structure, we found no brood and only a very few workers per site. Distinguishing these structureless pavilions were small turrets around the entrance holes (see attached photo), built of sand and soil particles, perhaps glued to a thin silken framework. Our tentative judgment is that these pavilions, accessory to the central nest site, may enhance aeration of the structureless and shallow (several cm-deep) cavity via the Bernouli effect, much as do the turrets of Myrmecocystus mexicanus in the Chihuahuan Desert of the U.S. We cannot rule out the occurrence of turrets in at least some central nest sites, since we have located just one such site to date. Both the pavilions with turrets and the central nest site initially lay hidden beneath leaf litter.      Arboreally nesting Polyrhachis species may be polydomous out of necessity, e.g., due to constraints of leaf sizes, etc., that do not apply to terrestrial nesters. However, we believe that the new species, like many of the Polyrhachis species encountered, relies on harvesting dispersed and perhaps low quality resources and may therefore benefit from splitting up the worker population, so as to position small numbers of workers in different regions of the home range which they regularly visit. Finally, and in contrast to other formicines such as Formica and Camponotus, which adamantly fend off their would-be destructors with vicious bites, the Polyrhachis workers were not aggressive toward us as we excavated their nests. Roy Snelling notes "that my observation has been that Polyrhachis species typically are inoffensive and not at all inclined to defend their nests".
So in the end, it was the plants, and not the ants, that were dangerous.



Editors note: The discovery of a new Polyrhachis is hardly surprising, given that probably not much more than half of the SE Asian ant fauna has actually been described. Polyrhachis species are often reclusive and, in the presence of amimicry complex, it would be easy to overlook a previously unrecognized species. ROY R. SNELLING

Pavilion turret of 'Polyrhachis new species'
Preserved specimen of P. 'new species'