The eyes have it

[Harlequinmania]

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Justin Marshall of the University of Queensland in Brisbane, Australia, and colleagues are examining the capability of mantis eyes to track objects.  Primates (including ourselves) can scan a field of view 200-300 times per second.  The mantis doubles that number.  These rapid eye movements likely help with tracking, clubbing or stabbing as they have no other mechanism of immobilizing their crustacean and mollusk prey.

Locking onto and tracking objects with fast eye movements are called saccades.  Saccades are a common phenomenon used by animals with image-forming visual systems, but in this case, they are unique.  According to Marshall, “[this ability] implies a ‘primate-like’ awareness of the immediate environment that we do not normally associate with crustaceans.”  Mechanically, this could be related to the response time of a photoreceptor being longer than the time a given portion of the image is stimulating that photoreceptor as the image drifts across the eye.  Mantis shrimps are the only crustaceans known to possess saccadic eye movements.

To learn more about mantis shrimp, read James W Fatherree's "An Introduction to Mantis Shrimps."

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Journal reference: Philosophical Transactions of the Royal Society B, DOI: 10.1098/rstb.2013.0042

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