Crossed-eye stereo, covering an area about 0.14mm x 0.18mm on subject.
The preceding is a crop from this whole frame, which covers about 0.37mm x 0.56mm on subject (APS-C at 40X NA 0.80). This is the side of the prothorax and part of one wing cover.
Since I first photographed one of these beetles, now almost 17 years ago, I have been struck by the odd appearance of the scales.
At modest magnifications such as 10X NA 0.30, the scales appear to be cylindrical pegs, tapered toward each end, with the outer end blunt and indented or maybe with a hole in it.
At the higher magnifications we see here, that impression is only reinforced. Following is a closer crop of the same area shown above.
However, appearances can be deceiving!
I scraped some scales off a beetle and floated them in a small drop of ethanol on a microscope slide. They self-assembled into a sort of raft, and when the ethanol had evaporated I was left with a dense strew of scales.
This layout reveals a previously hidden surface of the scales, the one that faces inward toward the beetle.
Seen this way, we can appreciate that the scales are not shaped as they appear to be from the outside. Rather than having a convex cylindrical structure as suggested by the outer surface and the blunt end, each scale actually has a prominent concave groove on its inner-facing surface.
The overall shape is pretty much as if it started out to be convex everywhere, but then partially "deflated" so that the inner surface collapsed toward the outer surface far enough to become concave. But this is just a description of what it looks like. I expect that the scales actually grow into this final shape in an efficient process that also builds in structural cross-bracing.
I do not recall ever seeing a description of how scales like this form. I have seen such descriptions for lepidoptera wing scales, but unfortunately the links have rotted and I cannot quickly find current ones.
As best I recall, each scale is formed by one cell, preferentially elongating away from its base by building internal structure, eventually leaving an essentially hollow shell, which R.F. Chapman in The Insects: Structure and Function (4th Edition, page 190) describes as follows:
Clearly some of the details are different, but I expect that the general development process and overall structure is similar. At least I can reasonably match everything I see in these images with that idea.A flattened scale consists of two lamellae with an airspace between, the inferior lamella, that is the lamella facing the wing membrane, being smooth, the superior lamella usually having longitudinal and transverse ridges. The two lamellae are supported by internal struts called trabeculae. The scales are set in sockets in the wing membrane and are inclined to the surface, overlapping each other to form a complete covering.
I hope you find this interesting! If anybody has further information or corrections, please share.
--Rik
Technical details: Canon R7 camera with Nikon 40X NA 0.80 M Plan apochromat, 253 frames focus-stepped at 0.5 micron, Zerene Stacker synthetic stereo at +-4 degrees (8 degrees total separation). Three flashes surrounding single layer of diffuser from an LED tube, ISO 100, 1/4 sec full electronic shutter with mid-exposure flash using a custom controller.
