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Reptile News – Surprising New Study on Snake Eyes and Vision

Herp enthusiasts are a lucky bunch, as we never need to wait too long for the next new discovery.  I’m especially thrilled by those that are completely unexpected, and which change “what we know” about animals and their lives.  The past few years have been especially productive, with news of Reticulated Pythons that regularly attacked people (Philippines), skin-feeding tadpoles, communal skinks, lung-less frogs and so much more (please see the articles linked below).  Recently, a Waterloo University researcher was startled to discover that snake spectacles (eye-caps) contain a maze of blood vessels.  These would seem to interfere with vision.  Intrigued, he investigated further…and made discoveries that broke new ground in snake biology.

Diamond Python shedding

Uploaded to Wikipedia Commons by Peter Ellis

Eye Caps Gain New Respect

Snakes view the world through fused, transparent eye lids known as the spectacles, brille or eye-caps.  Perhaps because they are shed along with the skin (please see photo), hobbyists and herpetologists alike have long considered them to be mere “goggles” that protect the eye while allowing for vision.  But we know have evidence that the spectacles are dynamic structures that assist in vision, and change according to the snake’s needs.

According to an article published in the current issue of the Journal of Experimental Biology (Nov., 2013), snakes can optimize their vision by controlling blood flow to the spectacle.  When stressed, blood vessels within the spectacle constrict and cut off blood supply to the area.  Vision then becomes clearer, because there is no blood within the vessels to interfere with images.

When a snake is not threatened by danger, the vessels expand and contract in a regular rhythm, allowing for optimum blood flow to the spectacles.

During the shedding process, the spectacle’s blood vessels remain dilated, and a steady supply of blood continually flows to the area.  Additional research is needed to fully explain this aspect of the phenomenon.

Coachwhip Snake

Uploaded to Wikipedia Commons by Fjguyote

Questions and Future Research

Coachwhip Snakes, Masticophis flagellum, (please see photo) were used in the experiments.  Native to the southern USA and northern Mexico, these diurnal, active snakes have huge eyes, and are considered to be sight-oriented hunters.  Certainly those I’ve tried to approach saw me coming from far-off – I never got close!

I wonder if other snakes have evolved the same degree of blood-flow control.  It would also be interesting to learn if Coachwhip Snakes restrict blood flow to the eye when hunting.

Future research will focus on the actual mechanics of the process.



Further Reading

People as Python Prey

Tadpoles that Consume Father’s Skin

Lung-less Frog

Communal Homes of Great Desert Skinks

About Frank Indiviglio

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Being born with a deep interest in animals might seem unfortunate for a native Bronxite , but my family encouraged my interest and the menagerie that sprung from it. Jobs with pet stores and importers had me caring for a fantastic assortment of reptiles and amphibians. After a detour as a lawyer, I was hired as a Bronx Zoo animal keeper and was soon caring for gharials, goliath frogs, king cobras and everything in-between. Research has taken me in pursuit of anacondas, Orinoco crocodiles and other animals in locales ranging from Venezuela’s llanos to Tortuguero’s beaches. Now, after 20+ years with the Bronx Zoo, I am a consultant for several zoos and museums. I have spent time in Japan, and often exchange ideas with zoologists there. I have written books on salamanders, geckos and other “herps”, discussed reptile-keeping on television and presented papers at conferences. A Master’s Degree in biology has led to teaching opportunities. My work puts me in contact with thousands of hobbyists keeping an array of pets. Without fail, I have learned much from them and hope, dear readers, that you will be generous in sharing your thoughts on this blog and web site. For a complete biography of my experience click here.
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