medicine episodes

Brownian Motion: the Ants

It’s a beautiful August day, and I’m sitting by the fire pit in the backyard with a beer watching the ants that have colonised the ground under the patio stones continue their work of excavating and moving the sandy substrate, grain by grain. It was these critters that provided the impetus for this week’s show; about a week or so ago my roommate and I sat here watching them do their work in a more or less haphazard fashion. While most of the foraging workers found their way back to the nest without difficulty, a few of the more geographically disinclined seemed to meander this way and that, occasionally dropping their cargo as if the seed or sand grain they carried were to blame. Of course, geographical inclination has nothing to do with it as foraging ants follow systems of pheromone trails. And chitinous hand-held GPSes.

Ants have been around since the Cretaceous, and since then have diversified into at least 12,000 species among 21 subfamilies and nearly 300 genera. They’ve colonised every major landmass except for Antartica, Greenland, Iceland, and a few islands in Polynesia, including the Hawaiian archipelago. Whether generalists or specialists, they occupy important positions in their ecosystems, comprising up to a quarter of the terrestrial animal biomass. They practice animal husbandry, agriculture, and are probably the most potent engineers of their environment outside of humans. They even fought MacGyver to a draw! Is it any wonder people like Brian Fisher and Walter Tschinkel would go to great lengths to study them?

On the show, I described Brian Fisher as “the Indiana Jones of myrmecologists.” That was a mistake. In actuality, Indiana Jones is the Brian Fisher of fictional archaeologists. If you think this is an exaggeration, listen to interviews on his profile page at the California Academy of Sciences, read this article from the March 2006 issue of Discover, and consider whether it takes more bullwhips to do it all for fortune and glory or for the sake of science.

When Dr. Fisher isn’t fighting malaria and power-tripping border guards to escort a vacuum cleaner bag full of ants to a museum, he’s busy working on AntWeb, an internet resource with the goal of documenting every described ant species in text and photos. At the time of writing, AntWeb has 14,062 species listed, and 4,243 of them photographed. (AntBase, another online myrmecology resource, has 12,571 species catalogued.) But reading and looking at pretty photos aren’t the only things you can do at AntWeb (or, will be able to do—AntWeb’s most detailed information is currently limited to the Neartic and Malagasy regions while global information is available at the genera level): you can overlay species distribution maps on Google Earth; download regional or species-specific field guides; compare your favourite formicids using the ant image comparison tool; or let the site do all the work for you as you enjoy a beverage and snack of your choice while watching a slide show of ants by genera. For a full list of the site’s capabilities, consult the ‘AntWeb Tools’ menu.

Dr. Walter Tschinkel’s work isn’t as death-defying as Dr. Fisher’s (or maybe it is—he studies the harvester ant, Pogonomyrmex badius, members of whose genus generally score 3.0 out of ~4.0 on the Schmidt’s Sting Pain Index), but it certainly is as fascinating.

His faculty page at Florida State University lists several areas of active research. I really encourage you to read through them, though as a fan of eusocial hymenopterans I’m drawn to sociogenesis (the growth and change of a superorganism such as a hive, akin to an individual organism’s embryogenesis), colony reproduction, neighbouring colony population dynamics, and foraging organisation (not all food sources are equal and foragers are allocated accordingly, at least among fire ants). However, the work for which Dr. Tschinkel is probably best known is his investigation of the 3-dimensional structure of ant colonies.

His method is to pour orthodontal plaster or liquid zinc down ant holes until the entire nest is filled, and then excavate the whole thing. He uses plaster when he wants to examine the distribution of ants in each tunnel and chamber, zinc when he wants a less fragile model of the nest. (I don’t feel nearly as bad now about pitting different ants against each other in plastic buckets when I was young, though to be fair Dr. Tschinkel actually produces publications from his experiments.) Ant colonies vary in size and complexity by species, ranging from a few hundred in a two or three chambers within a cubic metre to hundreds of millions of ants over a thousand cubic metres. Or so we thought. A comparison of cuticle hydrocarbons and an investigation of aggression levels between members of Argentine ant colonies in Europe, California, and Japan led researchers to suggest the three colonies might actually comprise one global super-colony of related ants.

Suddenly, I don’t feel so threatened by those Wasmannia auropunctata I encountered in Hawaii all those years ago.