Science is a community endeavor. Much of our knowledge is unwritten, and subsists in the hive mind of our collective social unit. Some of the cooler and bolder — and perhaps more important — ideas are the ones that might not make it to print. My fellow ecologists don’t publish most of what we know, as Mike Kaspari recently reminded us with a quote from Dan Janzen.
We rarely share our piles of negative results, or the little curiosities for which we can’t find the time. Getting a peer-reviewed paper out the door is a non-trivial amount of work, and just mentioning it in a conversation is easier. But, hey, I have a blog where I can mention this stuff.
So let me tell you about two things that I find rather weird, but haven’t put more resources into figuring out.
The first weird thing is a bottomless pit in the rainforest which is made by ants. Or so it seems.
I’ve worked intermittently with gypsy ants in the lowland rainforest in Costa Rica. Unlike most other ants, they have relatively wide open nest entrances, from the size of a nickel to the size of a quarter. I’ve dug up the nests. They’re shallow. But really, they act like a bottomless pit.
This forest has clay soil, like many rainforests. Once the soil is wet, it doesn’t accept much water. I’ve tried to flood gypsy ants out of their nests to collect colonies. If you quickly pour water down their nests (at a rate of about 5 liters per minute), the nest will flood and they’ll attempt to evacuate, fighting against the current with their brood. But then, some of them drown or get stuck or whatnot, and that’s not good for either of us.
So I then tried pouring the water down slowly, at the rate of about 2 liters per minute. (About 30 seconds for a nalgene bottle.) No ants emerge. And the nest doesn’t flood. Like, ever. On a few occasions, I’ve poured liter after liter after liter after liter after liter into the ground. But the nest didn’t fill up. The actual volume of this underground is well less than a liter. But if you pour water in at a moderate rate and don’t stop, then it doesn’t ever flood. (And the ants are fine.) Which, considering the composition of the soil, pretty darn amazing. Clearly, these ants are selecting or constructing sites that are exceptional at draining surface water when it floods into their nests. How are they doing this? What do they do to their nests to keep from being flooded out? I have no idea. Weird, huh? If this kind of edaphic stuff is up your alley, maybe we could figure it out.
The second weird thing are the blind ants that can’t smell. Or so it seems.
Those gypsy ants that have nests that don’t flood? It turns out that they keep moving from nest to nest, back and forth between a few nests, like they own three or four apartments and when they get tired of one after a few days, they move into another one, or so I’ve worked out. Why do they do this? Well, I’ve built up evidence of a few kinds that they’re constantly avoiding army ants, who attack them. The nests accumulate their odor, which attracts army ants. There’s one problem with this story: army ants can’t smell their prey as far as we know.
Army ants must rely on smell. They’re blind. The sensory world of ants relies on pheromonal communication. Another kind of ant (Cataglyphis) can smell a cookie from hundreds of meters away. And we know that army ants follow scents laid down on their trails, and respond to volatile odors when other ants release an alarm pheromone. So, they smell. But do they actually find they prey by sniffing them out? You’d think so. But we actually don’t know if this is true, as far as I know.
When I was trying to sort this out, I came on aside in Bill Gotwald’s 1995 book on Army Ants. It said something along the lines of (and this is a paraphrase as the book is in my office and I’m on sabbatical), “It’s assumed by many that army ants locate prey by odor, but there is no evidence that they do so.” If I take Gotwald’s word from it 20 years ago, and from what I know of army ant papers in the meantime, then I think we still don’t know.
There’s been plenty of work on army ant foraging behavior. But it’s kind of hard to test whether a roaming horde of hundreds of thousands of ants is smelling out its prey or chose it by some other mechanism, or just arbitrarily bumped into it. You can even bait army ants, but you won’t know if they just bumped into the bait and decided to stick around, or if they smelled the bait. (I’ve run some y-maze experiments on individual army ants from different locations in the raiding front, with a nice juicy prey colony at the end of one size of the maze, and that was the first time that I’ve gotten a p value equal to one.)
So, army ants might smell their prey. Or maybe, they don’t. Nobody has shown it yet, at least that I’m aware of. Which you’d think would be a straightforward thing. I think my next approach would be to see what prey odors their antennas pick up, or don’t pick up, using an electroantennogram (wherein you pluck off an antenna, waft odors over it, and find out when signals fire to the brain. Handily, you don’t have to run this by IACUC.) Someone want to schlep one down to the jungle this spring or this summer? But this is pretty low on my priorities, unless the right collaborator magically emerges.
If you sat down with a bunch of us, I imagine you could quickly collect hundreds of brief, “I wonder how this is?” or “This is something I thought would happen but didn’t and that’s a headscratcher.” I thought I’d unload two of these here, and if you have any you’d like to share, please do.