June Beetle eyes have a smoothly curved surface

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rjlittlefield
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June Beetle eyes have a smoothly curved surface

Post by rjlittlefield »

In a recent thread about the Lesser Stag Beetle, Dorcus parallelipipedus, it was pointed out that the surface of the eyes was oddly smooth, with only a hint of the ommatidia that surely must be there.

I thought I had seen that effect before, so I checked my collection of old specimens.

To my delight, I quickly found two specimens that are worth showing. Both of them are "June beetles", members of the scarab family that THIS reference says is closely related to the stag beetles.

This first one is particularly nice, though it may take a little study to recognize why.

This image is a crossed eye stereo pair. If you can see stereo, it may gradually become apparent to you that several of the large golden hairs in the upper part are actually "copies" of other hairs in that same area, reflected from the mirrorlike surface of the eye.

Image

This seemed a little too extreme to be true, but I confirmed by direct manipulation under a stereo scope that those really are reflections. Move one hair with a pin, and its partner that appears below the surface moves in just the same way, nudged by a reflection of the pin. It's quite unexpected. The reflection of the geometrically straight pin, not shown here, indicates that surface is slightly dimpled, presumably with one dimple for each ommatidium.

By the way, the golden reticulated pattern is caused by separation of internal tissues when the specimen dries. In live beetles and fresh specimens, the eye is almost black.

I do not know exactly what species this is. I find the adults occasionally in summer, on a sidewalk near a lighted wall at a local building. Here is a picture of the beast:

Image

The other specimen is a classic Ten-Lined June Beetle, collected some 28 years ago, that I used for my first experiment with telecentric lenses, 15 years ago. It can be seen in overview HERE.

The following is not a stereo pair. I mention this because I have accidentally tried several times to fuse it up. That actually works, but because the views are identical except for lighting, the stereo geometry looks flat.

The point of this pair is structure revealed by the lighting. On the left, with a strong specular reflection from the surface, you can see that the surface is slightly dimpled. But on the right, with very diffuse lighting so the surface does not show, you can see that the same area of the eye has shows the ommatidia structure strongly revealed in some of the golden bands.

Image

The following is a stereo pair. The interesting thing here is that there's a clear separation between the smooth but dirty surface, and the hexagonal grid of ommatidia bolow it.

Image


I hope you find this as interesting as I do. :D

--Rik

Technical: Closeups with 10X Mitutoyo stacked at 0.005 mm, cropped to show what I wanted. Diffuse illumination by electronic flash far back from a 3" diameter hemispherical diffuser; hard illumination for surface reflections using a single Jansjo lamp placed directly against the same diffuser. Synthetic stereo at +- 6 degrees.

Pau
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Re: June Beetle eyes have a smoothly curved surface

Post by Pau »

The stereos are not just nice but fully adequate to show the structure and to illustrate the concept =D>
Pau

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Re: June Beetle eyes have a smoothly curved surface

Post by MarkSturtevant »

Smoooooth! Or nearly perfectly so.
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Re: June Beetle eyes have a smoothly curved surface

Post by micro_pix »

Fascinating! The stereo images show the structure perfectly.

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Re: June Beetle eyes have a smoothly curved surface

Post by BugEZ »

Very interesting in this non aquatic beetle. I have seen a similar smooth eye surface in Dobsonfly eyes.I had presumed it was because the eye was designed for hunting under water?

Can it be that the ommatidia are open ( transparent) and the cornea forms a camera lens, a bit like nocturnal moth eyes?

K

Edited to add link to Dobsonfly photos

https://www.photomacrography.net/forum ... fly#p99836

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Re: June Beetle eyes have a smoothly curved surface

Post by quenoteam »

Oooooooooooh Rik is amazing, I never saw anything like it

BugEZ
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Re: June Beetle eyes have a smoothly curved surface

Post by BugEZ »

This figure from Nilsson’stext suggests nocturnal beetles may have a rather smooth cornea exterior surface. A feature of a “superposition” eye.

https://www.researchgate.net/figure/Ap ... _313690273

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Re: June Beetle eyes have a smoothly curved surface

Post by rjlittlefield »

Thanks for the feedback, guys! I'm glad to hear that the stereo works for other people also.
BugEZ wrote:
Fri Jul 16, 2021 5:13 pm
This figure from Nilsson’s text suggests nocturnal beetles may have a rather smooth cornea exterior surface. A feature of a “superposition” eye.
This makes sense from an optical standpoint, since in a superposition eye, the optics at each ommatidium have to provide light to a large number of sensors and thus a large field.

So then, perhaps the challenge is to explain the large fraction of beetles that have the clearly distinct lenses we are used to seeing.

Quick search on coleoptera apposition superposition turned up this article, which I found interesting in many respects: https://www.physoc.org/magazine-article ... -the-dark/ .
How nocturnal insects see in the dark
My journey studying the physiology of vision in nocturnal insects
Eric Warrant
Lund Vision Group, University of Lund, Sweden
--Rik

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Re: June Beetle eyes have a smoothly curved surface

Post by Troels »

Very interesting!
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Re: June Beetle eyes have a smoothly curved surface

Post by BugEZ »

Rik wrote
Quick search on coleoptera apposition superposition turned up this article, which I found interesting
Wow! Awesome! Many thanks for the article.

Eric Warrant is one of the authors of Visual Ecology which is an interesting read
K

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