Every night I hear my little hermit crabs clicking shells as they scurry around their tank. After a while I started to wonder, how can they see at night?
I wasn’t sure so I did some research.
Hermit Crabs can see in the dark because of their compound eyes. These consist of thousands of tiny ommatidia (individual eyes), which allow them to maximize light input even in the darkest places.
Turns out hermit crabs rely on much more than just their thousands of tiny eyes to get around. Let’s take a look at how the hermit crab manages to see, even in the pitch dark!
A Hermit Crab’s Many Eyes
I have two cats which I let out every night before I go to bed. Sometimes I’ll see one run across the yard chasing God knows what. We live in a very rural area so I’m not as worried about cars, but that’s beside the point.
I learned from my mother, who studied animal behavior in college, that cats can see in the dark because they have a high number of rods in their retinas. These rods are sensitive to dim light, which let cats be able to see just fine with 1/6th of the light we humans need.
That always fascinated me as a kid and after getting my hermit crabs I could only assume their eyes worked the same. But after a few Google searches, I was quite surprised!
It turns out that hermit crabs do not see the same way that cats, or you and I, do. They have compound eyes, like insects.
Have you ever looked into a kaleidoscope as a kid that made you see a bunch of whatever you were looking at? If so, that’s how your little hermit crab sees the world.
In nature, it works out to the crab’s advantage to be nocturnal. There aren’t as many seagulls flying overhead when it gets dark out. To achieve this, hermit crabs have thousands of ommatidia (organs that consist of corneas, lens, and other cells that make up an eye) arranged in a way to maximize even the smallest light intake.
Doing this gives the hermit crab the ability to see just fine even with a minuscule amount of light.
How Antennas Help
Even with their thousands of eyes, the amount of light they’ll get is less than we’ll be able to use in a room with very dim lights. Just enough to see where you’re going but stub your toe along the way.
These clever crustaceans have a way around this: their antennas. I’m sure you’ve seen their little antennas poking away wherever they’re looking at.
Like their eyes, their antennae are the crab’s sensory organs that allow him or her to gather information about its surroundings.
Hermit crabs have two pairs of sensory appendages (antennas), one long and one short. The longer antennas are used to tough and feel, while the shorter pair is used to smell and taste.
We’re going to focus on the longer antennas. They are what hermit crabs used to feel their way through the dark like a blind man with a cane.
Their eyes are better for picking up movements (how could you miss with thousands of eyes?) than feeling their way around objects. That’s what their antennas are for.
At night, (especially if they are in dark environments) they use mainly their antennas to feel their way and determine their paths.
Do They Need a Night Light?
It’s easy to think that maybe turning on a light will help your crabs navigate their tanks just a bit easier. Well, your heart’s in the right place, but that might do more harm than good for your hermit crabs.
Hermit crabs have 12-hour light cycles and 12-hour dark cycles. When the sun goes down and the lights go out, hermit crabs take this darkness as a sign to wake up from their long day of slumber. Sounds like me as a teenager!
Adding a night light will throw off their sleep schedule, making them think it’s daytime when it’s actually not.
This can be disappointing if you want to view your little crabs scurry around at night. If you try to flick on a light, they’ll just hide in their shells.
A great way to get around this is to buy a red “night” lamp or purple “moonlight” lamp. I found an aquarium LED night light on Amazon that fits perfectly over my 10-gallon tank. It comes in different sizes for larger tanks, so be sure to check it out.
The LED night light is perfect because it keeps the lights dim to take the shape of moonlight and will not mess with my crab’s sleeping schedules. Plus it lets me view my crabs when they’re most active.
Do They Sleep?
With all this nocturnal activity, you may wonder when hermit crabs actually sleep.
It’s common knowledge at this point that hermit crabs are nocturnal. They like to be active after dark, and only move around during the day to take a drink or nibble at some food.
This will most likely be when the house is quiet. Hermit crabs are timid creatures and like it when it’s dark and quiet.
Every hermit crab is different, but my two crabs like to dig a little bed under their log to sleep in. That’s where they spend most of their day.
Other crabs like to hang on a cage with only their legs sticking out to sleep.
Related Questions
Can hermit crabs see colors?
Hermit crabs are believed to see an array of colors like we humans can. It’s also speculated that hermit crabs can see the ultraviolet and infrared range, but it has not been proven.
How do hermit crabs keep their eyes from drying out?
I’ve never seen a hermit crab blink, how do they keep their eyes moist?
A think membranous-like layer cover’s a hermit crab’s eyes. This thin layer of their exoskeleton contains moisture, keeping their eyes safe and well functioning.