Do snails have eyes and what’s their vision like?
23 June 2022
Discover facts about snail vision
From time to time, we look into the differences in vision across the animal kingdom. This is because the structure of the human eye is so different to that of a cat, bat or shark, and the variations are absolutely fascinating. You can discover more about the incredible structure of the human eye on our blog. While we’ve written about a few different creatures before on this blog, we’ve never looked into the vision of snails. Their eyes are on top of stalks and, incredibly, they use the sense of touch near their eyes to help them navigate. While human eyes are typically 24mm in diameter, snail eyes are no more than 1-2mm in diameter. So, if you too have been wondering about how snails see, then wonder no more as you’re in the right place!
What is the structure of a snail eye?
There are several different types of snails and their vision varies from one to the other. Land snails, which are the type you are most likely to see in your garden, have two pairs of stalks – sometimes called tentacles – on the top of their head. Snails have an eye at the top of each taller stalk, allowing them to see any obstacles or predators nearby. Whilst we humans have to turn our heads in order to look around us, land snails can actually turn their stalks without moving their bodies, providing them with a great field of vision. The smaller stalks are used to feel around the snail, giving them a method of detecting obstacles without even needing their vision.
Having a wide field of vision is especially important for snails as the quality of their sight is actually very low. Humans and a range of other animals have the ciliary muscle in the eye. This muscle allows your lens to focus on objects at different distances, meaning that your eyes can adjust to better see objects both near and far away from you. The fact that snails’ eyes lack this muscle means that a lot of what they do see is unfocused and blurry, and they have to manually focus their eyes using the stalks. On top of this, snails do not have colour vision, so their vision is in black and white, as well as being fuzzy.
While their actual eyes might not be especially useful for seeing with, snails actually have light sense cells covering their entire bodies. This means that, even without eyes, they can sense when a shadow casts over them. It usually means a predator is nearby so this reflex allows snails to go back into their protective shells to hide from danger. They can also retract their eyes when they hide inside their shells, and then pop their stalks out to assess for danger, whilst still hiding in their shells. Snails have an excellent sense of smell to make up for their poor vision. Different breeds of snails have different diets and, interestingly, the carnivorous snails have much better vision than their omnivorous counterparts, in order to track and capture their moving prey more accurately!
Learn more about animal vision
If you enjoyed this post about snails’ eyesight and how it compares to our vision, you may also be interested in the following Optimax blog posts:
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