Last Updated on February 27, 2024 by Joanne Harper
Hermit crabs’ eyes and vision function differently from humans.
They allow hermit crabs to see 360 degrees, assist with motion detection, and give them good night vision. While humans lack these traits, we share their ability to see color.
Hermit crabs see the world in blue and yellow, called dichromatic vision.
This means hermit crabs only have 2 color receptors that allow them to see 2 color combinations. Hermit crabs are nocturnal animals, requiring only enough photoreceptors to see well in the dark.
Color is essential in the lives of hermit crabs, as they use it to select shells and detect predators. They’re most receptive to blue, which they find alarming, but they see most other colors as shades of grey.
Can Hermit Crabs See Like People?
Hermit crabs’ eyes don’t look or function entirely like human eyes. However, some people share visual traits with hermit crabs regarding how they see color.
Hermit crabs have two photoreceptor cells called rods and cones. The rods are used to:
- Perceive wavelengths.
- Detect motion accurately.
- Function best in low-lighting.
- Only see black and white.
The problem with rods is their poor image detail, but cones are used to:
- Detect color wavelengths.
- Perceive color.
- Have sharp image detail.
- Function best in bright light.
To balance that, cones have poor motion detection. Both humans and hermit crabs use rods and cones in tandem to see more clearly, depending on how much light is available.
During the day, the cones constantly work so that hermit crabs can see the world in sharper detail.
The rods take over at night so things can be better distinguished in the dark. That’s true, even if the image lacks details and color.
How Many Colors Can Hermit Crabs See?
The cones are responsible for detecting color. For humans, there are three different color channels available through them. These can detect the wavelengths of:
- Red.
- Blue.
- All color combinations.
Beings with three color channels are called trichromats, which is why humans differ from hermit crabs. Hermit crabs only have two color channels:
- One for blue.
- One for yellow.
Their cones can only detect these two colors and all the other combinations in the blue-yellow and grey spectrums. For this reason, they’re called dichromats: beings with only two color channels.
Dichromacy isn’t only found in hermit crabs, though. While rare, this particular color blindness is found in humans as well.
Are Hermit Crabs Color Blind?
Hermit crabs are partly color blind, so they can’t see the same range of color as humans.
Seeing color has many advantages, as it helps organisms distinguish between different objects and determine what is dangerous and what isn’t. Color vision also speeds up partner selection during mating season and can even help when hiding from predators.
It may seem like hermit crabs are at a disadvantage, but it works out well for them from an evolutionary standpoint.
The need to see a wide range of colors depends on when they’re most active. Diurnal creatures (those most active during the day) have far more cones than rods because they mostly use their eyes when there’s lots of sunlight.
Since humans operate during the day, we see a broader range of colors. Since hermit crabs don’t have this dilemma, they have good night vision.
Hermit crabs also have other defense mechanisms that compensate for their lack of color. For example, they can bury themselves in the sand and retreat into their shells when in danger.
These ensured they never needed to develop more color receptors to detect predators.
Do Hermit Crabs Like Color?
Hermit crabs like color because their ability to pick out their ideal shells depends on their ability to see the different colors and shades in that shell. Hermit crabs use their blue-yellow vision to see which new homes will be the most vibrant and appealing.
Hermit crabs are crustaceans with vulnerable exoskeletons. For this reason, they routinely choose shells they can move into, which are more robust and better able to protect against predators. As they grow into adults, they grow out of their shells, requiring them to look for new ones.
Given how vital shell selection is to a hermit crab’s survival, the process involves a lot of decision-making. One aspect includes deciding if the color of the shell is suitable for the individual hermit crab.
Do Hermit Crabs Like Colored Shells?
According to the Journal of Experimental Biology, hermit crabs are more likely to choose shells that:
- Match the color of the background
- Have low levels of contrast
In a study, researchers presented them with new shells once hermit crabs had chosen shells to occupy. They matched the background even better than the original ones.
Despite this, the hermit crabs refused to leave the shells they chose. This led researchers to believe they would trade having a poorly camouflaged shell over being vulnerable while switching.
When choosing shells for hermit crabs to move into, get shells that match the color of their environment.
The hermit crabs will choose a shell anyway (since it’s better than being vulnerable). However, they’ll feel safer knowing they chose a shell that camouflages them well.
What Colors Stress Out Hermit Crabs the Most?
According to the University of California, hermit crabs were presented with varying shells in different:
- Colors.
- Contrasts.
- Brightness.
- Orientations.
Researchers documented how hermit crabs responded to different visual stimuli.
It was initially theorized that hermit crabs would be least responsive to blue and green colors. After all, their natural habitat in the ocean was primarily made up of those two colors.
However, hermit crabs repeatedly hid in their shells when presented with blue shapes. So, they detected blue objects as threats, responded mildly to green shapes, and barely reacted to red shapes.
It’s true that hermit crabs are motion-sensitive and hide whenever they detect movement. Eliminate blue objects from their tank. Instead, put green and red objects in their environment to reduce stress.
