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Moving black spots on the eyes of a mantis

 
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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Tue Aug 07, 2007 7:54 pm    Post subject: Moving black spots on the eyes of a mantis Reply with quote



If you get close enough to see it, many insect eyes have a small black spot that follows your every move. This mantis makes a great example.

How does the mantis do that? It's an optical effect. Not an illusion, mind you -- there really is a small black spot that moves around on the surface of the eye. The catch is, the small black spot is not some physical structure that's moving, it's just the set of ommatidia (facets of the compound eye) that happen to be facing in the direction of the observer -- either your eyes or the camera.

This has one fascinating effect, though. If you look at the mantis eye through a stereo microscope, then each of your eyes sees the black spot in a different position. Your brain then proceeds to interpret the different positions as parallax caused by depth, and what you see looks for all the world like the mantis's compound eyes are big transparent balls, with the black spots painted on the inside of the eyes' back surfaces! Now that's an illusion -- and a very bizarre but convincing one!

--Rik

Technical: Canon 300D, Sigma 105 mm at 1:1, natural light, cropped. Captive mantis.
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Mike B in OKlahoma



Joined: 04 Aug 2006
Posts: 1048
Location: Oklahoma City

PostPosted: Tue Aug 07, 2007 9:30 pm    Post subject: Reply with quote

Very interesting montage, thanks! (and I got an "error 500" when I tried to access it first time).
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Mike Broderick
Oklahoma City, OK, USA

Constructive critiques of my pictures, and reposts in this forum for purposes of critique are welcome

"I must obey the inscrutable exhortations of my soul....My mandate includes weird bugs."
--Calvin
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rjlittlefield
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PostPosted: Tue Aug 07, 2007 9:53 pm    Post subject: Reply with quote

Thanks, Mike, for both comments.

BTW, I just noticed that the two frames in the lower right corner actually make a usable stereo pair (crossed-eye), if you concentrate on just the eye and ignore the legs and antennae. I'll try to get a better stereo pair tomorrow, but no promises -- it's a challenging problem.

--Rik
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Erland R.N.



Joined: 07 Aug 2006
Posts: 334
Location: Kolding, Denmark

PostPosted: Wed Aug 08, 2007 10:50 am    Post subject: Reply with quote

Great photo sequence, displaying the effect very nice indeed. I mostly see it on dragonflies, and I've read that there infact should be I think six secondary spots around the main spot. They are probably hard to see though.
I would stay away from a stereo-microscope, to keep sane :-)
I must say that when I've held a dragonfly in my hands with very big eyes, and moved it very close to my own eyes, the surface seems to float too. Maybe the same effect.

Erland
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Erland R.N.



Joined: 07 Aug 2006
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Location: Kolding, Denmark

PostPosted: Wed Aug 08, 2007 10:51 am    Post subject: Reply with quote

btw. the pose in the upper left picture is awesome.
Erland
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Raul G



Joined: 18 Jul 2007
Posts: 79
Location: MEXICO CITY

PostPosted: Wed Aug 08, 2007 10:56 am    Post subject: Cool Shots Reply with quote

Cool shots
I love live specimens.
It is alive?.....isn't it?
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rjlittlefield
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PostPosted: Wed Aug 08, 2007 5:11 pm    Post subject: Re: Cool Shots Reply with quote

Caronte wrote:
It is alive?.....isn't it?

Oh yes, very alive. That's why it's challenging to get a stereo pair, given that I don't have a camera that will shoot both pictures at the same instant.

--Rik
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rjlittlefield
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PostPosted: Wed Aug 08, 2007 9:29 pm    Post subject: Reply with quote

Erland R.N. wrote:
I've read that there infact should be I think six secondary spots around the main spot. They are probably hard to see though. ... I must say that when I've held a dragonfly in my hands with very big eyes, and moved it very close to my own eyes, the surface seems to float too. Maybe the same effect.

I think dragonfly eyes and mantis eyes are slightly different. I have only been able to find the one black spot in this mantis. (See larger image here.) Many butterflies, on the other hand, have numerous fuzzy dark spots that behave roughly the same way. The size, sharpness, and number of the spots may have to do with the resolution of the eyes, but this is just my speculation -- I have not read anything about it.

--Rik
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rjlittlefield
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PostPosted: Sat Apr 25, 2009 4:21 pm    Post subject: Reply with quote

A follow-up posting, showing the spots as a stereo pair, can be found HERE.

--Rik
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