Physics Photo of the Week

November 1, 2013

Preying Mantis Eyes




Preying mantises Sphodromantis viridis are amazing predators, and often found lurking in bushes at this time of year.  They will eat any insect or arthropod that ventures too close to these watchful compound eyes.  Notice how the insect can rotate its head to get a better view of potential victims or a possible predator of the mantis (such as a bird or person).  Click on each image for a larger view of the preying mantis.

Insect eyes are compound eyes, unlike human and other vertebrate eyes.  The external eye contains tens of thousands of external receptors called omatidia.  Each omatidia consists of a tube that is oriented toward the outside surface of the eye spheroid.  A separate photo receptor lies at the base of the tube.  These eyes resemble vertebrate retinas - but on the outside of the eye, not at the focus of a single lens.  Insects see images without lenses.  Each omatidium has a unique direction in space, so the insect with such large eyes can see in almost every direction. 

These images are different views of the same mantis.  Notice the pupil-like dark spot on each image.  This is called the "pseudo pupil".  To the camera or human viewer a small area of omatidia are oriented along the viewers line of sight.  Since we (or the camera) see directly into the base of the selected omatidia, we see darkness, not the walls of the omatidium.  Notice that the location of the pseudo pupil is in a different part of the compound eye for each of the photos above as the camera has a different angle relative to the insect's eye.  For catching other insects for prey, the mantis' eyes are highly developed.  We cannot see the individual omatidia in the mantis eyes, whereas most insects' eyes have much larger and noticeable omatidia.  This corresponds to a digital camera with more pixels.  The mantis has high resolution vision.  Because of the omnidirectional nature of insect compound eyes, most insects do not turn their heads to "focus" on a particular object.  Because the mantis can rotate its head, I suspect that the insect has a special region of more highly sensitive and concentrated omatidia, similar to the fovea in human eyes that are absent in most animals.

This mantis was alive for all these photos and was allowed to continue lurking for its dinner.

A dead dragonfly's eyes were featured in an earlier Physics Photo (Nov. 18, 2011).


Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to dcollins@warren-wilson.edu.

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