Early April is early autumn in northeastern Argentina, but seasons just south of the Tropic of Capricorn bear little resemblance to the well-defined spring, summer, fall and winter that we are accustomed to in eastern North America. Early fall here is not a riot of color, pungent smells, and sharp shadows cast from an oblique sun, but rather dull greens and browns, muted and dusty after eight months under a searing overhead sun with only the sparsest of rains for the past two. Such conditions are generally not conducive to insect life, and for the most part insects that live in warm, seasonally wet environments adapt by timing their adult activity (the time for reproduction) to the moist seasons—which in this part of Argentina means September through January. Thus, despite warm temperatures and a subtropical environment, early April is not the best time to be looking for insects here.
Pseudomyrmex sp. | Corrientes, Argentina
Nevertheless, not all insect groups respond in this fashion, and one in particular is as ubiquitous and diverse now as at any other time of year—ants! I had to trek into sand and mud along the Rio Paraná to find tiger beetles (a few), and it took some dedicated searching to ferret out a few stands of late-season blooming plants and fresh-cut woodpiles to encounter a small diversity of longhorned beetles. I think I may have even seen a single jewel beetle, a chrysobothrine of some type, as it landed on and then flash flew away from the same woodpile with which I had modest longhorned beetle success. The ants, however, have been everywhere—no tree, shrub, or square meter of ground is without them in astounding diversity of size and form.
At this point it appeared to be eating something it plucked from the bark.
I probably shouldn’t admit this, as I hear rumor there are a few myrmecologists that frequent this blog, but I have a hard time getting excited about ants. I know, their unique social structures and evolutionary history are among the most fascinating in the insect world, and watching their behaviors is a lesson in charisma beyond reproach. Still, however, for me there are just so many of them and their taxonomy so completely foreign to me that every time I try digging further I feel immediately overwhelmed. Coleopteran taxonomy may be an order of magnitude more diverse, but since I only pay attention to about 1.5% of the order, it’s as comfortable to me as an old shoe.
There is one group of ants that I do find endlessly fascinating—the genus Pseudomyrmex. I don’t know why that should be the case—there are plenty of other ant genera that seem to have the tools and structures that usually grab my attention (e.g., grossly oversized mandibles, sharp spines, heavy duty surface sculpturing, etc.). Pseudomyrmex spp. have none of these morphological gimmicks—just a simple, elongate, wasp-like form. Perhaps it’s their association with branches (like wood-boring beetles) rather than the ground—nope, tiger beetles are decidedly ground dwellers and I dig them (Get it? Heh!). No, it must be their super-sized eyes. Most ants have beady little eyes that make it hard to look into their soul. Pseudomyrmex eyes have charisma—you can see them looking at you (and almost read their thoughts).
Anyway, among the many ants that I’ve noted wandering the banks of the Rio Paraná here in Corrientes are these smallish, orangish Pseudomyrmex spp. This particular individual was the first one I saw, revealed when I happened to pull away a bark chip from trunk of the palm tree on which it was hiding. It wandered all over the palm trunk for the next 15 minutes or so as I chased after it with my 65mm lens. For such tenaciously crawling subjects I’ve found that simply firing off shot after shot as you track it in the view-finder rather than waiting for it to pause and trying to compose each shot is the best way to get some usable images. It’s simply a numbers game—the more shots you fire off, the better chance you have that at least some will be in-focus, nicely composed, and well-lit. These are the ones I was happiest with from the session. (And, OMG, did I really just give advice on how to photograph ants?)
It goes without saying that a more specific ID, if possible, would be greatly appreciated (should any prominent myrmecologists happen across these photos). There are scads of species in this genus right across the river in Paraguay, and presumably the diversity in Argentina is similarly high.
Copyright © Ted C. MacRae 2012