Calm waters, frenzied beetles

North Fork River - Ozark Co., Missouri

The North Fork River in south-central Missouri, like most Ozark rivers and streams, flows clear and cold over gravelled bottoms. Sustained year-round by the numerous seeps and springs that result from the region’s unique Karst geology, it meanders through a mix of forest and woodland alongside massive bluffs of half-a-billion-year-old dolomite. While small rapids can be found where gravel bars approach the bluffs, for the most part the shallow waters course lazily and idyllically south toward the White River in northern Arkansas.

Dineutus sp. (poss. discolor, per Brady Richards)

Lazy waters are the domain of whirligig beetles (family Gyrinidae).  We encountered this ‘raft’ of beetles in a sheltered pool near the shore of the North Fork River while hiking the Ozark Trail last October.  These frenzied little beetles live almost exclusively on the surface of the water, where they feed on organisms or scavenge debris in their famously and erratically conspicuous aggregations.  Such behavior might make them seem vulnerable to predation, but in actuality the reverse is true.  Beetles in rafts benefit from the increased number of eyes that can better scan the environment for potential threats than can individual beetles (Vulinec and Miller 1989), and the larger the raft the more efficiently this occurs.  There is also evidence that the appearance of the rafts themselves is a signal to warn potential predators (primarily fish) of the noxious chemicals produced in the beetles’ paired pygidial glands (Ivarsson et al. 1996), despite the decidedly non-aposematic coloration of the beetles themselves.

Photo Details: Canon 50D w/ 17-85mm zoom lens, natural light. Photo 1 – 17mm, ISO 100, 1/25 sec, f/5.6; photo 2 – 85mm, ISO 500, 1/160 sec, f/5.6. Typical post-processing (levels, minor cropping, unsharp mask).


Ivarsson, P., B.-I. Henrikson and J. A. E. Stenson.  1996.  Volatile substances in the pygidial secretion of gyrinid beetles (Coleoptera: Gyrinidae).  Chemoecology 7(4):191–193.

Vulinec, K. and M. C. Miller. 1989. Aggregation and Predator Avoidance in Whirligig Beetles (Coleoptera: Gyrinidae). Journal of the New York Entomological Society 97(4):438–447.

Copyright © Ted C. MacRae 2011

“Trying” to photograph whirligig beetles

Nobody figured out exactly what I was doing in the photograph shown in the previous post (does anybody now see the whirligig beetles in the lower left corner of the photo?), but I sure enjoyed the guesses.  Several people alluded to dropping the camera or falling into the water, while others mentioned my heretofore unrevealed contortionist abilities.  However, Morgan Jackson‘s tale of trying to photograph Platypsyllus castoris has it all – rarely photographed species and the inordinate lengths we go through to get the shot.

Of course, whirligig beetles (family Gyrinidae) are much more commonly encountered than Platypsyllus castoris, but they can’t be any easier to photograph.  I spotted them as Rich and I balanced our way across a massive sycamore tree trunk while crossing the Black River during our early April hike of the lower Wappapello Section of the Ozark Trail.  I don’t know much more about whirligig beetles (or aquatic insects in general) than your average land-lubbin’ entomologist (in fact, I don’t think I’ve collected any since college systematics – yes, that long ago!), but for some reason I felt the need to try to photograph them.  Sure, the fallen tree provided a rare opportunity to get reasonably close to these very skittish insects without having to wade, but I think it was actually just the challenge of trying to photograph something in constant zigzagging motion that appealed to me.  Rich’s warnings that I would drop my camera were not enough to dissuade me, and after reaching the other side I ditched the backpack and tiptoed out with just my camera.

It seems like I’ve said this often in recent months, but these are my new hardest insect to photograph.  Not only are there the usual difficulties of framing and focusing a subject that is always in motion, but that motion is fast, erratic, and unpredictable, making tracking through the lens an extraordinary challenge.  Moreover, balancing precariously on a debris pile in the middle of the river strains the body and adds an element of danger (yes, I would be in deep doodoo if I dropped that camera).  I kept my eye on one particular individual that was swimming nearest to me, and after watching for a bit I saw that it was making a relatively predictable circuit that passed fairly close to me each time around.  I started trying to follow it through the lens and snap shots as it passed by – most of them turned out like this (actually, most of them turned out worse than this):

However, with each pass I got better, and I started getting shots with at least part of the beetle in focus.  So intent I was on what I was doing that I didn’t even know Rich had taken the photograph of me in the previous post until he showed it to me afterwards (he said he wanted to document the camera drop!).  Eventually I got this shot:

It’s far from a perfect photo – I had to adjust the levels because I hadn’t figured out the best lighting to use for something on the water’s surface, and the specular highlights from the flash on the forward elytron are rather extreme.  But the entire beetle is in focus, and we can make a reasonable guess as to its identity.  There are only two genera of whirligig beetles in Missouri – Dineutus and Gyrinus – and the large size (~12 mm in length) and hidden scutellum clearly identify this individual as something in the former genus.  Moreover, the rounded elytral apices (seen on other individuals as well) narrow it down even further to just a few possible species.  Unfortunately, they are distinguished primarily by ventral coloration; however, the bad first photo clearly does show dark legs, suggesting this may be D. ciliatus and not the orange-legged D. emarginatus.  I don’t even really care what species it is (did you ever think you’d hear me say that?), I’m just happy to have gotten a reasonably good photograph of an insect that surely few people have photographed well.

Copyright © Ted C. MacRae 2010

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