Moving black spots on the eyes of a mantis

[rjlittlefield]

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.

[Mike B in OKlahoma]

Very interesting montage, thanks! (and I got an "error 500" when I tried to access it first time).
_________________
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

[rjlittlefield]

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

[Erland R.N.]

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

[Erland R.N.]

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

[Raul G]

Cool shots
I love live specimens.
It is alive?.....isn't it?

[rjlittlefield]

[rjlittlefield]

[rjlittlefield]

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

--Rik

[Irisoratoria]

Dear rjlittlefield.

The effect of the paying mantis coumpound eyes is called "pseudopupil" and it is an optical ilusion created because the omatidia aligned with the observer absorb the light while the non aligned omatidia reflect the light, creating a curious effect.
_________________
Albert

www.albertlleal.com