When Ants and Physics Collide: Traffic Jams

It has been about 8 months since my last post, and since then I have returned from China and begun my Ph.D. program in the Committee on Evolutionary Biology at the University of Chicago. More information on this work is here.

To start off the resumption of my blogging, I leave you with today’s NPR story on ants and how they prevent traffic jams: here.

(iStockphoto image from the NPR piece)

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The Ants, the Physicist, and the Larder

The great physicist Richard Feynman, like all brilliant men, had a fascination with ants. I mean, how could this guy not like ants?

In fact, one of his books, Surely You’re Joking, Mr. Feynman!, includes a rather lengthy anecdote, or rather a series of anecdotes spanning many years, that detail experiments he carried out on ants. These largely focused on the nature of ants’ trail-making behavior. When in his Ph.D. program at Princeton, he casually tested some hypotheses about ant behavior using little paper ferries to carry ants back and forth from a food source. These experiments ended up having a practical benefit for him, as described in this excerpt:

In Princeton the ants found my larder, where I had jelly and bread and stuff, which was quite a distance from the window. A long line of ants marched along the floor across the living room. It was during the time I was doing these experiments on the ants, so I thought to myself, “What can I do to stop them from coming to my larder without killing any ants? No poison; you gotta be humane to the ants!” What I did was this: In preparation, I put a bit of sugar about six or eight inches from their entry point into the room, that they didn’t know about. Then I made those ferry things again, and whenever an ant returning with food walked onto my little ferry I’d carry him over and put him on the sugar. Any ant coming toward the larder that walked onto a ferry I also carried over to the sugar. Eventually the ants found their way from the sugar to their hole, so this new trail was being doubly reinforced, while the old trail was being used less and less. I knew that after half an hour or so the old trail would dry up, and in an hour they were out of my larder. I didn’t wash the floor; I didn’t do anything but ferry ants.

This is an excellent example of non-destructive “pest” control. To be sure, the ants probably returned the following year, and the year after that, but it is also unlikely that other “remedies”, like chemicals, would have permanently removed their presence. These critters are extraordinarily resiliant. It’s no wonder their collective biomass may match that of mankind.

 

Source

Feynman, Richard P. 1985. Surely You’re Joking, Mr. Feynman!

(H/T Ari).

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Ant Physics, Revisited

About two years ago today, I wrote a post, “Ant Physics“, that described, and provided the answer to, a mechanical physics problem given during Physics 140 at the University of Michigan. Now, a couple times each year, I get a spike of views on my blog associated with this page. Amusingly, these times correlate with upcoming exam dates, so I always know when Physics 140 students are frantically preparing for their exam in order to get an A or, like me, deciding to not frantically prepare and instead get their first and only C. Such a spike occurred today, and I see from UM’s calendar that finals begin this Friday.

You can check out the original post here, but this is the associated artwork I created for the question:

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Through the Eye of an Ant

A friend of mine recently shared with me a story from CNN in which humans, per Solomon’s instructions, look to the ant, consider its ways, and are wise. Researchers have developed a digital camera that actually mimics the eye of various insects, including the fire ant. Below is the image included in the article:

This is certainly an impressive feat, and may lead to advances in cameras for both wide-angle purposes and small spaces like those in the human body. Less impressive is the inclusion of the “fire ant” in the photo, which is, incidentally, not a fire ant (genus Solenopsis). I believe that this is actually some sort of Pheidole species, but I’m not sure. I was first suspicious due to the rugosity (bumpiness) of the exoskelton, which is not something I typically associate with the rather smooth fire ants, but two other definitive traits soon presented themselves. The first is the presence of spines on the “propodeum”, the last segment of the “mesosoma” (the middle section of the ant which looks like a thorax, but is actually both the thorax and part of the abdomen fused to the thorax). Solenopsis species lack such spines. The second trait is the number of segments of the club of the ant’s antennae. Solenopsis species only have a two-segmented club, while this individual has a four-segmented club (like in some Pheidole and other genera). See the image below:

So, in summary: cool discovery, bad taxonomy.

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Bal-ants

A recent paper in PLOS ONE deals with an interesting topic: ant kinematics. The study investigated the physiological adaptations used in grass-cutting ants (Atta vollenweideri) to avoid falling over. To this end, the researchers set up a somewhat elaborate contraption that is able to record the movements of the ants. See Figure 1 from the paper:

 

They found that the ants used an “alternating tripod gait”, which basically means that cycles of movement for each set of legs overlapped (with the fore and hind legs of one side in phase with the mid leg of the other). Furthermore, “the overlap was greatest for ants carrying long fragments, resulting in more legs contacting the ground simultaneously”. The researches report some other results as well, but it should be clear that this study is an interesting one.

I tried thinking of applications for these results, and I could only come up with the military. With the government’s potential interest in insect drones, such research could aid the development of more realistic, and therefore better camouflaged, robo-bugs.

 

Citation:

Moll K, Roces F, Federle W (2013) How Load-Carrying Ants Avoid Falling Over: Mechanical Stability during Foraging in Atta vollenweideri Grass-Cutting Ants. PLoS ONE 8(1): e52816.

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Ant Physics

I am currently enrolled in Physics 140, General Physics I, at the University of Michigan. As can be imagined, my professor, Dr. Yuri Popov, rarely discusses the physics of ants. But a week or so ago, he broke from this usual monotony to present the following problem:

An ant with mass m is standing peacefully on top of a horizontal , stretched rope. The rope has mass per unit length μ and is under tension F. Without warning, Cousin Throckmorton starts a sinusoidal transverse wave of wavelength λ propagating along the rope. The motion of the rope is in a vertical plain. What minimum wave amplitude will make the ant become momentarily weightless? Assume that m is so small that the presence of the ant has no effect on the propagation of the wave.

First, I take offense at the idea that an ant has “no effect” on anything, let alone the propagation of a sinusoidal transverse wave! But that aside, I have illustrated this problem below:

Unfortunately, I could not get a photo of Sir Francis Throckmorton, but I trust that this picture of Francis Walsingham will suffice. I also took the liberty of making the educated assumption that the ant in question is Cephalotes atratus, the gliding ant (shown here).

If one can ignore the animal cruelty manifest in this situation, one will find that the answer to this question is [gμ(λ^2)]/[4(π^2)F], where g is the force of acceleration due to gravity. But the real question is: why am I not studying for my Physics final occurring this Friday? One will not find an answer to this question.

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