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Post by leilani on Oct 27, 2009 22:13:10 GMT -10
I've seen this before but never really gave it much thought until today. I'm hoping someone clever out there might help me better understand just what is going on. Here is a pitcher with a fair number of tiny ants that somehow appear to be trapped not just in the pitcher but in the center of the pitcher pool. The ants struggle but, the interesting part is, their struggles appear to continually drive them toward the center of the pool. The first questions that come to my mind are .... Q1: Is this phenomena a function of the pitcher fluid or of some sort of mis-directed ant response regiment? I can't help but wonder .... "if that one ant would just let go of the others could he not save himself". Q2: If, it is a function of the pitcher fluid then, what dynamics or principles are involved?
If you were to ask me ..... then, I'd look you in the eye and tell you that the fluid dynamics become non-Newtonian at this scale and the harder and faster the ants struggle the less stable the fluid becomes. like trying to climb out of an hourglass they are drawn inexorably to the center. If you appeared to believe me then, I would smile.
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Dave Evans
Nobiles
dpevans_at_rci.rutgers.edu
Posts: 490
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Post by Dave Evans on Oct 28, 2009 7:48:28 GMT -10
I don't know about any special property of the pitcher fluid, but since the column of water is in a tube, the water maybe clinging to the inside of the pitcher wall. If the edge of the water is a little higher than the rest of the water surface, the ants will fall to the lowest point in the center...
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Post by shawnintland on Oct 28, 2009 12:44:51 GMT -10
Those synchronized swimming maneuvers require deep water. If they tried it in the shallows they'd never get a good score!
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Post by walterg on Oct 28, 2009 12:49:44 GMT -10
Perhaps the ants are instinctively driven to congregate. Or maybe their little spiny legs are just getting hooked on each other. Dave's explanation seems pretty convincing, though.
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Post by leilani on Oct 28, 2009 23:00:02 GMT -10
Trapped in the meniscus Interesting idea but I would think this effect would be rather small. These are very tiny ants and there should be enough surface tension for them to basically walk on the water. I think there is more going on here. When you watch the video it is clear that many seem to orient themselves toward the edges of the pitcher but are frustrated in their efforts to get there. I think I read a study somewhere that suggested a reduced surface tension in pitcher fluid. (The idea being that the insects sink and die quicker.) But these are very small ants and they don't appear to be sinking ( .. although they will eventually) but look more as if they are slipping or being drawn (or repelled) to the center of the pool.
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Post by walterg on Oct 29, 2009 5:15:32 GMT -10
I hadn't noticed that it was a video. Duh. It looks to me like the ants are just frantically seeking some foothold and in doing so are drawing themselves together with the movement of their legs.
Imagine a similar number of sociopathic people thrown overboard together, each one desperately out for himself, trying to climb on top of the others to get his head out of water while at the same time trying to avoid being pushed under by everyone else. I specify sociopaths to avoid the obvious antropomorphization issues. Ants are social insects who can cooperate in some extraordinary ways, yes, but their intelligence is limited, and in this situation desperation would be the rule.
I think the ants are just trying to escape, and since another ant offers better foothold than the pitcher wall, they end up crowding together.
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PHaze
Urceolatae
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Post by PHaze on Oct 29, 2009 12:31:44 GMT -10
Dave's meniscus hypothesis could be tested by sprinkling some pepper or other tiny buoyant substance in a pitcher that is similar, but empty.
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Post by jgriffin on Oct 29, 2009 16:02:32 GMT -10
Thanks for pointing out it's a video(duh to me too). It looks like to me they are trying to climb up on what's available, which happens to be each other.
Joe
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Post by leilani on Oct 29, 2009 21:24:22 GMT -10
The next video I post will be CLEARLY IDENTIFIED. Look! I want answers. Make something up if you have to. Dave ..... The gravity theory. Maybe, but not on its own. Sure, water in a column forms a meniscus but the incline formed is relatively small. After all, ants are very good at walking uphill, downhill, upside down, etc. It certainly can't be that they lack power for such a small incline .... walking or swimming. Walter .... stupid ant panic but likes the gravity theory. (Saying ants are like crazy people is still suggesting that ants are like people.) I'm not sure. I would think "procedure" might rule. There may well be enough ants to initiate bridge building ..... but not enough to complete the bridge. (If, they only had more ants then, they could cross the water and begin trying to scale the walls.) This would still not explain why they are in the middle. PHaze .... An even better test would be to just put the same number of ants in a comparably sized tube of regular water and see if they get stuck in the middle. (I would do the experiment but that would be ..... "scientific".) jgriffin ..... I've got you down for stupid ant panic but liking the gravity theory
I sticking with some fluid property. In light of some special property of the fluid ( .. reduced surface tension, non-Newtonian dynamics, a lessened specific gravity, etc. ) the meniscus effect would, perhaps, make a difference. How about this one ..... The molecular surface of the pitcher fluid is composed not of water but of that super-slippery substance (with its special fluid properties) that drips into the pitcher from the peristome. Am I the only one with no credibility to lose? How about an electromagnetic theory .... The ants and the walls of the pitcher carry electrical charges that repel the ants to a point equidistant from the surrounding walls. or ... Pitcher fluid is more dynamic than we suspect and exhibits micro-currents of fluid rising faster along the smooth surfaces of the pitcher wall and then washing to the center of the pitcher where it flows back, in a down-draft, into the pitcher drawing the ants with it. Come on! ...... pseudo-science is fun.
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Post by shawnintland on Oct 30, 2009 4:14:57 GMT -10
Hmmmmm. Is it harvest season over there or what? ;D I hadn't realized it was a video either!
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Post by walterg on Oct 30, 2009 6:00:55 GMT -10
More than happy to contribute my half-baked musings to the thought-salad. I suppose "desperation" would be the right word for socipathic people, but not for ants. How about just "instinct"? My point is that altruism would not take the day, unless the ruling instincts were to save the group rather than the individual. Along those lines, I thought about ants' bridge-building behavior, too. It might not work in a slippery-sided pitcher unless an awful lot of ants were involved - Enough so that they could climb on top of each other all the way to the peristome. Of course, that doesn't mean they wouldn't try. Maybe what you see is a rudimentary manifestation of that attempt in a species that has not evolved it's behavior as far as army ants have. I can't even begin to speculate about the interactions of gravity, surface tension, and fluid dynamics in such a small scale situation. Ants are tiny compared to the fluid forces involved, and they are monstrously strong for their size, so maybe gravity would have a negligible effect. I'm not a real scientist. Sounds to me like you've got an Earth-shattering scientific study to do in the highland nursery in 2010. I've got some test tubes. Mabye you could get the natives to throw some mainlanders into Hilo Bay for a comparison.
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Post by dvg on Oct 30, 2009 6:43:05 GMT -10
That's an interesting problem you have posed for us Leilani, and I am also curious as to why the ants seem to stay in the middle of the pitcher.
I read an article in 'New Scientist' magazine, published back in June 7-13 2008. The piece written by Stephanie Pain, was entitled 'Gotcha', and dealt with Nepenthes pitcher's trapping mechanisms.
Of interest here was that a couple of French scientists, Laurence Gaume and Yoel Forterre, found that the
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Post by leilani on Oct 30, 2009 8:15:24 GMT -10
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Post by witzelsucht on Oct 30, 2009 15:23:59 GMT -10
So I'm not sure what you'd call this but it sort of reminds me of how difficult it is to remove a small bit of eggshell from a bowl of eggs. As you push the bit of shell toward the edge of the bowl it always wants to slide away from your finger just as you've almost got it to the edge. It's probably something to do with viscoelasticity but I'll call the albumen theory.
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Post by rsivertsen on Oct 30, 2009 16:03:13 GMT -10
There are known wetting agents in the Nepenthes fluid as well, which gets into an insect's surface layer that otherwise, in plain water would form a protective layer of air that would enable it to escape. Some of these things were the subject of a few graduate student's dissertation during the early 80's but I never got a copy or reprint of any of them.
Getting a flying insect too wet, and heavy to fly away to escape is a very strategic method of capture for Nepenthes to have evolved. It also probably clogs their ability to breath.
There was some speculation some time ago that the larger insect's attempts to escape by swimming and stoking the side walls of the pitchers, might remove the waxy scales that line those walls of the pitchers (known as the "waxy zone"), may prompt the pitchers to produce more digestive enzymes, but these things were never really pursued to my knowledge with any conclusive findings, but an interesting thought nonetheless.
- Rich
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