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.
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.
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.