It may have been the angle of light on the water, at that hour and in that season, but it was also the magic of multiple minds that caused me to pause long enough to see what I might otherwise have passed by. The minds were those of Mariah and her graduate student friends from the Princeton School of Public and International Affairs, who came three weeks ago to help at Herrontown Woods. After a midday workday, pulling some last remnants of stiltgrass along Barden pathways before their seeds dropped, we walked down to the stream. I wanted to tell them the story of the improbably large fish I had seen there back in April, but we soon focused in on something much more diminutive.
After a long late-summer drought that continued into fall, there was just enough water to host a gathering of water striders calmly zigzagging about on the waters's surface in the rocky stream. I pointed them out, thinking we'd note their novel buoyancy and move on. But the students took an interest, bent down to look more closely and, because they enjoy each other's company, began talking about what they were seeing. One observation led to another, and before I knew it, we began seeing aspects of the water striders we hadn't noticed before. What were those bright points of light where the striders' feet touch the water? And why did their tiny feet make such comparatively big shadows on the streambed?
It occurred to me that their feet make dimples in the water's surface that serve as tiny curved mirrors, reflecting focused light up towards us while casting shadows on the streambed.
As with any natural phenomenon, the internet is packed with information to amaze and edify. AnimalScienceTV has an excellent video that lauds the water striders' quick reflexes and appetite for mosquito larvae. Water-phobic oily hairs help keep them high and dry. Water striders can be preyed on by an aquatic bug called a backswimmer, which looks like a water boatman.
All this enlightenment began with an auspicious angle of light on the water, and a synergy of minds.
Water striders are always a treat to watch
ReplyDeleteHas anyone (to your knowledge) measured the energy expenditure of water striders striding (that might require a very small enclosure, and training them to avoid "fixed" walls as the water flows under them), as opposed to hopping (which they do if you chase them onto streamside rocks) and flying (which they can do for short distances if really put to it)? That must rank right up there with measuring the work efficiency of a cicada buzzing (they can be persuaded to do that for long periods by holding them between forefinger and thumb)!
ReplyDeleteIf insects were machines, they would be considered beyond the beyond in their efficiency and strength relative to the their size. I believe the video linked to in the post says that the striders have an alternative motion they use at times to keep up with the current. That would be very creative to actually measure their energy expenditure.
DeleteI think the "alternative motion" might be an artifact of the motion description by the observer -- interrupted movements vs. a continuous propulsion. I do wonder just how they achieve traction on the water surface -- purely frictionless bouyancy wouldn't allow them to do anything other than quiver in place. So there must be oriented microstructure to their foot-pads, perhaps hairy functional ridges which engage (drag) for the power stroke, and automatically (even passively) retract for the return stroke? The characterization in one video of "making ripples and riding them forward" is likely to be as inefficient as gunneling (or gunwhaling, however it's spelled) a canoe?
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