Dineutus discolor (Aube, 1838) – C.L.P. #2

I apologize for not having written yesterday – I’ve been rather caught up in family matters (to the extent, in fact, that I had to return to Toronto yesterday).  I’ll be at the cottage again tomorrow.

Today’s entry centers on Dineutus discolor, a member of Gyrinidae (ergo, an example of what has been termed a “whirligig” beetle).  Whirligig beetles inhabit the surfaces of water bodies; one can often observe them there, carving their circular trajectories upon being even moderately alarmed.  It is this of their traits that earns them their name.

Albeit that they may seem like a children’s toy, there is far more to these peculiar beetles than at first meets the eye.  To begin, they are fascinating in that they are semi-aquatic, in addition to inhabiting the surfaces of water bodies rather than their depths.  Noting that they lack particularly-tailored integuments, the surface tension that all small animals living in this environment must deal with presents rather a challenge to these energetic beetles.  Fortunately, their legs have evolved into powerful propellers – in fact, as Nachtigall (whom I admire greatly) described some decades ago, Gyrinus substriatus, a species of whirligig commonly found in Europe, morphs eighty-four percent of the energy that it invests into swimming into thrust!

Of course, whirligigs are also affected by fluid and wave resistance.  This results in their moving forward in what are known as “propulsion episodes”, as defined by Voise and Casas – periods of combined acceleration and deceleration respectively, where the former results from the beetle’s employing one of the three types of strokes commonly attributable to it, and the latter happens by dint of resistance forces.  Calculating the effect of resistance forces on the beetles in relation to size and leg kinematics is truly fascinating.  Chepelianskii presents an equation for wave drag:

Formula

Where Pext(k) is the pressure source, and Pext(k) = p0 exp(−kb), with b being the size of the object, and p0 the total force exerted on the surface.  Immediately, we can see how results would vary with D. discolor – it is, after all, significantly larger than G. substriatus.

The fact that I’ve just alluded to: the vast majority of the research conducted in this area revolves around the physical and behavioral characteristics of G. substriatus – it would be fascinating to see what could be explored with relation to D. discolor, as the two display several noteworthy differences.

On a somewhat related note, I would very much like to study the possibility of these beetles employing an echolocation system.  It has been established that they utilize surface waves to avoid obstacles, to hunt, and to do a wide array of other things.  They have also been found to propagate waves, and it has been suggested that these might serve the beetles in much the same way.  I’m thinking of setting up an observation aquarium with about six of these guys, and hopefully encouraging them to breed – I’d like to note the differences in the stroke pattern when the beetles’ activity is constrained, as well as any irregularity that this imposes upon their trajectories.

In addition to all of this, whirligigs exhibit a survival technique that is largely fascinating – their tendency towards grouping.  It is hardly ever that one will see a lone beetle.  This is interesting primarily because the beetles order themselves, some resting on the outskirts of the group, and others toward the center.  In addition, they often exchange positions in light of changes have been made to their environment.  All of this can be linked to what I was discussing previously, as they also incorporate drafting considerations into their movements.  Observing their behavior in this particular sense could prove instrumental to the advancement of artificial social intelligence for autonomous robots, actually – ants, too, have been viewed in a similar light.

Anyway, without further ado, the beetles:

Original Video – More videos at TinyPic

My apologies, this is rather poor quality, but it does showcase their exchanging positions within the group – that was my goal in filming.

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