the Party Millipides of Panama
Sat, Mar 28, 2009 at 4:26 AM
I just came back from Panama, where I spent the past five weeks with my fellow Animal Behavior and Zoology classmates from the Evergreen State College. We were out in some secondary tropical lowland forest near our home base, looking for anoles, when I found a patch of freaky-looking critters clumped together on the side of a large, living, lichen-enrobed tree in a swampy part of the forest. At first glance I didn’t even take them for arthropods; they looked like crazy armored flatworms. There were about nine adults, with four or five younger ones (about a third the size of the adults) scattered among them. I whipped out my trusty specimen container (don’t leave home without it!) and collected two adults and a little one.
When I got back to our quarters, I showed them to Pete, who runs ITEC (the Institute for Tropical Ecology and Conservation, our very cool laboratory/dormitory/home- away-from-home). He confirmed my suspicions that they were a millipede, although he didn’t know the species. He noted that he’d often seen them, and that every time he had, they were in large groups with adults and young, like I’d seen, and in the open on the sides of trees. I was intrigued, and kept my eyes out for them for the rest of the trip.
Bizarrely, I next ran into them on a trail in the cloud forests surrounded El Valle, the crater of an extinct volcano. This was a big group, numbering over sixty, and in this group there were big white patches of REALLY young ones, like the little pale ones pictured here. Again, they were in the open, during the day, on the side of a large dead tree. I collected more specimens to keep my two at home company (the young one had died, but the two adults were living seemingly very contentedly in a habitat of moss and dead wood I’d made for them in a beaker). Unfortunately, this batch did not survive the trip through Panama City and back home to ITEC.
I next came upon them on a small dead tree overhanging a stream at the mouth of La Gruta caves, where we were batwatching. The undersides of the largest of the tree branches were covered in patches of white young, ringed by adults. The colony extended to the outermost stalactites of the cave. The midsized juveniles were scattered among the adults on the tree, but not among the adults on the stalactites or on the fallen branches caught in the dead tree.
I collected adults, young, and juveniles, and, after some experimenting (which I’ll spare you, as this message is already beyond overlong, but hey, you asked for “as much narrative and information as possible”, and by gods you’re going to get it) discovered that the adults stuck by their young, even if there was a disadvantage in terms of food/shelter (both are kinda the same thing for these guys) in doing so. Furthermore, the millipedes preferred the company of adults that they had been captured near, even after being Randomized (which isn’t nearly as ominous as it sounds).
I can’t for the life of me figure out why this might be. They don’t give off any detectable chemical defense, so their only defense seems to be armor, which would do their soft, pale babies not very much good. So why group them all together in a big white honking advertisement to the local insectivore population? They live on their food source, so I don’t think that feeding them is a motivator. Frankly, I’m puzzled. Any ideas, or recommendations of people who might have ideas?
For that matter, I’m not entirely sure what these guys even ARE. I keyed them out in an ancient book on the milipides of Costa Rica and Panama while I was in ITEC, and came up with Platydesmus subovatus, but there were no pictures and, not being an entomologist by training, some of the subtleties of the anatomy described escaped me. When I came back to the ‘States and was able to check online, I became more certain that they belong in the order Platydesmida. Beyond that, though, I’m lost; they frankly look like little dun clones of Brachycybe, which are Andrognathids, but from what (very little) I’ve been able to discern, Brachycybe is a genus that is limited to the continental United States. There are other Andrognathids that look, from pictures, a lot less like these guys, though, and I have yet come across a picture of any Platydesmid (the eponymous other family within the order Platydesmidae), so I can’t tell if the really different-looking Andrognathids are just highl y derived (meaning that the sluggy looking dudes like Brachycybe and my little guys are potentially just the basal look for the Platydesmid order) or if I’ve actually got a sister taxon to Brachycybe. Or maybe they just converged to look like robotic leeches. I really don’t know.
There are gods only know how many species of millipede in the Neotropics; I don’t expect anyone to pin these guys down to species given two rather blurry photos, but if you could help me get down to genus or even family I would be greatly in your debt! If you need better photos, that could be arranged; the animals I collected from La Gruta (and those original two from my first encounter with this species) have accompanied me back to Washington State, where they’re living in a colony in a large hexagonal tank full of rotten Panamanian wood and moss.
Colin Eliphalet Bartlett
the mouth of La Gruta Cave, Isla Colon, Bocas del Toro Archipelago, Bocas del Toro Province, Republic of Panama
Thanks so much for your detailed account of your observations of these social Millipedes from Panama. Sadly, we are uncertain of the exact identification, but we will post your letter and photo in the hopes that some Millipede expert will contact us.