Predaceous Diving Beetle

2015 July 22

Sandy found this in the parking lot up by the hospital in Hancock on April 11, 2015. This was pretty early in the spring, we were still getting regular freezes. She says she was talking to somebody when she spotted it, and surreptitiously captured the beetle without ever interrupting the conversation. And I’m glad she grabbed it, because the last time I photographed one of these beetles, it was long dead and its legs were mostly broken off, so I really needed another specimen to photograph[1]

The marked metal object behind him is a ruler, and the markings are 1/16 inch each. So he’s pretty close to half an inch long.

The color, particularly the pale marks across the rear part of the wing covers, look like the beetles in the genus Acilius, although I’m not quite sure which one.

This particular one is a male. We can tell from the enlarged pads on his front legs, which have suckers on the bottom that help him hold on to females while mating.

These beetles overwinter as adults in bodies of water that are large enough not to freeze all the way to the bottom. Then they fly in the early spring looking for mates, which is why Sandy found this one way up at the hospital on top of the hill, which is probably a quarter mile away from the lake.

This one was capable of diving, but mostly bobbed to the surface and sculled around using his long hind legs as oars. It looks like his head is just under the surface of the water, but his highly water-repellent back was out and practically dry. Here he is at the beginning of his swimming stroke:

and here he is at the end:

These beetles will lay eggs in pretty much any reasonably permanent body of water. Sandy has, in the past, even found the larvae in puddles of water on logging trails. The larvae are aggressively predatory, and eat things like mosquito larvae, other water insects, small slugs/snails, and when they get large enough even tadpoles and small fish. They mature in the fall, and then the adult beetles fly off looking for a good place to overwinter.

[1] This also gave a good opportunity to try out my “new” camera. I’d been using a Canon 10D digital SLR that I’d bought back in 2009, which at the time was a 6-year-old camera and “only” about 4 generations out of date. But now it is almost 12 years old, and 7 generations out of date (the current camera in the series is the 70D). And aside from being progressively more obsolete and being lacking in certain respects, it was also getting kind of flaky as far as whether it would actually take a picture when the shutter button was pressed. So, I jumped up the series several generations to a used Canon 40D, which is the camera that is currently in the price “sweet spot” – used ones are only slightly more expensive than the previous-generation 30D, but only half the price of the not-that-much-better 50D. In addition to having a higher pixel count (jumping from 6.3 megapixels for the 10D, to 10.1 megapixels for the 40D), the shutter response is much more brisk, the on-camera display is now 3 inches instead of 1.8, and it is moderately weather-proofed (I wouldn’t dunk it in water, but it is supposed to be OK in light rain or moderate dust). It probably won’t make the images here noticeably different most of the time, since I’m still using the same macro lens, although the bigger display is making it easier to tell whether the pictures are good or not (which should help avoid poorly-focused pictures like the cigarette beetle in the previous post). And, I still have to resize the photos in order to make them small enough to upload, so the pictures I post won’t be bigger. But it is making my life easier by being a handier camera.

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