Natural Connections: Underwater Eyes
By Emily M. Stone
Naturalist/Education Director, Cable Natural History Museum
The low, gray clouds of an approaching storm made the humid afternoon feel extra dark. Preparing to head home after work, I strapped on my bike helmet and latched my pannier to my rear rack. My sunglasses, however, got tucked into the back pocket of my high-vis vest. It was just too dark to wear them comfortably.
A few miles in, I came to regret that decision.
The county highway is scheduled to be repaved soon, and I bumped and swerved among the cracks, rough spots, and loose gravel. When a truck blew past me, barely getting over to pass despite a clear, straight road, its tires sent up a spray of sand and dust. Blinking, I could feel bits of fine grit in my eyes. Wouldn’t it be great, I thought, if I could have slipped on some eye protection just as the truck flew past?
In fact, many animals do have goggles that they can engage and put away at will. This third eyelid is called a nictitating membrane. This science word has great rhythm, and I love making students pronounce it with me: nik-ti-tey-ting. We have upper and lower eyelids, I explain, and these animals also have transparent or translucent eyelids that move horizontally.
Birds of prey like peregrine falcons use their nictitating membranes during high-speed dives in order to protect their eyes from dust and debris in the air, and also as windshield wipers to clean that dust off of their eyes and keep them moist. Nictitating membranes are often engaged at the point of attack, and sometimes while the chicks are getting fed, too. Actually, most birds, even little chickadees, protect their eyes this way.
After a few more miles of blinking opaque eyelids, my eyes felt ok again. By then, the bridge over the Namekagon River was coming into view. Even without sunshine, the afternoon felt uncomfortably hot, and the crystal-clear water of the river sparkled refreshingly. At the last second, I made my decision, checked my helmet mirror for cars, and swerved into the river landing.
The water there was only knee deep, but by sitting on the rocky bottom, I was able to cool off up to my shoulders. I reveled in the touch of the current supporting and massaging my back, and let my gaze relax into soft fascination with the patterns of light and the bed of eelgrass waving next to me like a river nymph’s hair.
When something bumped my bare ankle, I peered into the water and tried to squint past the surface glare. Even with polarized sunglasses now actually on my face where they belonged, I couldn’t make the shapes resolve into anything identifiable. Was that a fish? A crayfish? A floating leaf? A river monster?
I stood up and walked to shallower water. Still, any moving shapes were camouflaged beneath the surface glare. Oh sure, I could have put my face into the water and opened my eyes to see better, but then debris would wash in and my contact lenses would wash out. I’ve always struggled with getting swim goggles to seal, and anyway, I didn’t have any stashed in my bike panier today.
Once again, I thought longingly of nictitating membranes. Water animals have them too. Exotic ones like sharks, sea lions, crocodiles, and manatees, but also our locals, like beavers, frogs, fish, turtles, ducks, and loons can close their third eyelids underwater. While many mammals (like us) have lost this amazing adaptation, lions, cats, camels, polar bears, rabbits, aardvarks, and those busy beavers still have this cool trick in their eye pocket.
As I stood there wishing for a way to see underwater, a sudden jolt of brilliance hit me. My new Olympus Tough camera—with its waterproof casing—was tucked inside my panier. Within minutes I was hitting record and submerging it into the current. I couldn’t see to aim it, or hold it still in the surprisingly strong flow, but this was better than nothing. I pulled it out, stopped recording, and hit play.
On the LCD screen, dozens of small fish, about the size of cigars, each with a dark stripe from eye to tail, darted over mini hills of sand and among green plants. In one patch, chartreuse green algae undulated like soft feather boas in a graceful dance.
On the surface, all I could see was sparkling light and impressionistic shapes and colors. I could feel fish nipping at my ankles, but could see almost nothing. The world that the camera revealed was full of motion, light, color—and also life. Soft green fuzz topped the rocks, ribbon-like plants undulated playfully, and many sizes of those fish darted easily among the bubbles my wrists stirred up as they resisted the flow.
I may not have my own built-in swim goggles, but my underwater “eye” is pretty special, in its own way: I can share what it sees with you! Visit my blog or the Museum’s YouTube channel to watch the fish dart and algae dance. It may really open your eyes to what’s underwater!
Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.
For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is now open with our exciting Mysteries of the Night exhibit. Connect with us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.