Following is a crossed-eye stereo pair of one foot of a locust seed beetle, likely Amblycerus robiniae.
If you can see stereo, or trust your imagination to interpret the mono images, you can see that each hair of the yellow pad leads to a sharp bend, at a fork into two tines, each of which ends in a small enlarged pad. We'll be taking a closer look at those later.
But first, let's zoom out and look at the whole beetle.
It's about 8 mm long, and it grew up inside one bean of a seed pod on the large locust tree in my backyard.
The live adult is photographed here on a piece of locust pod. That's an emergence hole next to it, but almost surely not the exact one that this particular beetle came from.
Nonetheless I'm quite confident that this is a fair presentation, because last fall I collected a number of fallen pods with beetles still next to holes from which they might have come, and several pods still containing pupae from which beetles later emerged. That pleased me because always before I had just seen holes, with no good clue what might have made them.
I intended to photograph the adults last fall, to get an ID, but the options turned out to be so limited that I just decided they must be Amblycerus robiniae and moved on to other things.
However, Mother Nature apparently decided that I was slacking off and needed to pay more attention, because this spring more beetles repeatedly called themselves to my attention. First there were the two beetles that turned up clinging to pods that had fallen over the winter. Those came indoors to be watched under a dissecting scope while they climbed around the inside of a small enclosure that I made with cover slips. It was interesting behavior -- they could climb the vertical sides, but slowly slid down if they stopped moving, and they wouldn't attempt to transfer to the top at all. I was intending to photograph that, somehow or other, but I couldn't quite figure out how to do it and then the issue became moot the following morning when I discovered that I had left the enclosure sitting with one side open and both beetles were gone. Oops, no beetles! But also no worries -- I had other things to do anyway. Some days later my wife encountered a small bug she did not recognize, sitting on the floor at the top of some stairs. Yep, it was one of the beetles. I did not lose that one again, but I still couldn't figure out how to photograph it and gave up after a short attempt. Then another one turned up on the outside of a sliding glass door leading to my backyard. Sigh... So I collected that one, confined it for a while, again could not figure out how to photograph its interaction with the glass, and finally just turned it loose too. I was getting almost proud of my discipline at letting go of the problem. Then a couple of days ago my wife came to bed late, saying "Oh by the way, I left a specimen on your laptop". She wouldn't tell me what it was, and to be honest I didn't care much at that moment because I just wanted to go back to sleep. But the next morning, sure enough, the little plastic box sitting on my laptop contained another one of the dang beetles. My wife had found it clinging to a wall, not far from where the one had been on the floor. Was it the other beetle that had escaped my enclosure? I didn't know, it didn't matter, I took the hint -- Mother Nature was not going to let me walk away from this one.
Finally I was able to capture some decently in-focus frames that documented the foot-sliding-on-clean-glass behavior. Here is a short GIF of that -- just 5 frames but I think you'll get the idea. This is with a beetle clinging on the underside of a cover slip after I rolled the enclosure over. That way it didn't make any net progress, but each foot kept sliding toward the middle and periodically it would have to pick up a foot and move it back out.
Here is a closer view of the hairs. This is just a tighter crop from the earlier image, shot at a little over 10X using Mitutoyo 10X NA 0.28 with Raynox DCR-150 on Canon R7 camera.
Unlike some other hairy feet that I've looked at before, this one didn't seem to have any finer subdivisions. I did get a closer view, moving up to a Nikon 20X NA 0.75 objective on Raynox DCR-150 plus a 1.4X teleconverter, for optical 30X NA 0.75. That was a lot more trouble for just a little more information, basically just confirming there was nothing more to see optically. Here's a tight crop of that.
I went looking for SEM images of seed beetle feet. I couldn't find anything that exactly matched, but several top hits matched pretty closely. The hairs in panel "d" HERE (linked from HERE) look to have the same shape tips, although not the bend-and-fork structure farther down the hair. It's interesting that my seed beetle foot shows only one type of ends (two if you count the few that don't fork), while the foot in the paper has several forms in one pad. The one I've shot here is a hind foot. I have not looked to see if the other feet are different. In the literature there are also reports of species where the males and females have different sorts of hairs, apparently a matter of holding on while mating. Again I have no idea about these seed beetles, and I do not know the sex of the one that I photographed.
And that's enough for now. I hope that Mother Nature is satisfied for a while.
--Rik
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