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Do Hermit Crabs Eat Algae?

Many keepers of aquatic pets consider algae a nuisance. Left unchecked, algae can grow and multiply to unmanageable levels, which gives an aquarium a murky, unclean appearance.

Hermit crabs are ‘algae eaters’ for aquariums. Marine hermit crabs, in particular, eat algae.

Terrestrial hermit crabs will also use algae as a food source. However, hermit crabs can’t be relied upon to single-handedly manage algae in a tank, and not all algae are safe or edible.

Hermit crabs should be encouraged to eat algae as it keeps an aquarium clean. Marine hermit crabs are nature’s janitors, so understand the different types of algae that hermit crabs like to devour.

What Are Algae?

Algae is the collective term for a group of alga. They’re most commonly located in bodies of water, although they also grow on wood, stone, and soil. Some algae even grow on animal skin and shells.

Algae are often confused with plants. This is an easy mistake to make, especially aesthetically. Algae are not plants, though. Nor are they animals or fungi. Instead, as explained by Biosystems, algae belong to a group of organisms called protists.

Algae are critical to all living things, as they create oxygen. Even marine animals require oxygen to breathe, including aquatic hermit crabs. Algae also act as a food source for many marine lifeforms, including hermit crabs.

Algae come in a wide array of shapes and sizes. In some cases, you’ll need a microscope to detect algae. Left unchecked, though, algae can reach lengths of 200 feet or more. This is impossible in a home aquarium, but algae levels must be closely monitored.

Appropriate levels of algae in an aquarium are a positive thing. Algae will organically filter water, as well as provide food and oxygen. Algae also replicate a marine animal’s natural habitat.

Think of algae as weeds on a lawn. They start small but can drastically expand. Keeping on top of growth keeps an aquarium clean and aesthetically pleasing.

Can Hermit Crabs Eat Algae?

Hermit crabs are scavengers by nature. A hermit crab will never hunt down food unless it needs to. Even then, it prefers to target small targets, such as insects. As hermit crabs are more commonly predators than prey, they act as bottom-feeders on the ocean floor.

This means that algae have become a natural food source for hermit crabs. Marine species, which make up the majority of hermit crabs, are particularly fond of algae. Terrestrial hermit crabs also eat algae, as it provides essential protein.

Hermit crabs also enjoy algae because they are an easy, non-resistant meal. As per the Journal of the Marine Biological Association of the United Kingdom, land hermit crabs will gravitate to a substrate covered with algae. This ensures a plentiful food source.

Another reason that hermit crabs enjoy algae is they do not spoil. Hermit crabs like to eat little and often, as their small bodies cannot cope with gorging on a large meal. Algae provide a constant, reliable food source.

Many fish owners put hermit crabs in an aquarium as a natural algae clean-up crew. Hermit crabs after often sold by fish specialists under the banner ‘algae eaters.’ In this regard, hermit crabs perform a similar role to snails in a fish tank.

coralline algae

Will Hermit Crabs Eat Algae Wafers?

If your aquarium is short of algae, consider adding algae wafers. These are a food source most commonly offered to fish, so you’ll find them in any exotic pet food store.

Algae wafers are small discs created from compressed vegetables and dry algae. Drop a wafer into an aquarium and stand back. The wafers will soften up within a few seconds and sink to the bottom of the tank. Your hermit crabs can then consume the wafers.

Algae wafers serve many purposes. They act as a food source and a treat, should you wish to give your hermit crabs something special. Also, algae wafers in water can kickstart the natural growth of more organic algae – leading to more food for your hermit crabs.

Serve algae wafers to marine hermit crabs sparingly, depending on the size of your aquarium. A habitat that only hosts a handful of small hermit crabs, or is less than 20 gallons in size, should only receive half a wafer at a time.

Remember, hermit crabs do not eat much. Left too long, the wafer will start to cloud the water in an aquarium. If you offer these wafers to land hermit crabs, remove anything uneaten after 24 hours and replace it.

Types of Algae for Hermit Crabs

Algae come in a wide array of shapes, sizes, and colors. With over 27,000 different species, it’s impossible to profile them all. The algae profiled below are likely to be encountered by captive hermit crabs.

Bubble Algae

Bubble algae (Valonia ventricosa, or to use a colloquial nickname, Sailor’s Eyeball) is the largest unicellular organism in the world. This alga is a constant presence in natural water sources and is commonly found in a home aquarium.

Bubble algae is a shiny green spherical growth. Single alga can grow to the size of a tennis ball, but this is uncommon in a tank. All the same, bubble algae can grow to troublesome sizes. Every time bubble algae bursts, thousands more are released into the water.

This means that a hermit crab feasting on bubble algae is a simultaneous blessing and curse. Your crabs may eat these algae. As discussed, this will lead to more bubble algae, not less. Every time these algae are pinched or bitten, more are produced.

In moderation, this is a good thing. As discussed in Scientific Reports, bubble algae are linked to the production of Chlorella vulgaris. This is a rich source of protein, commonly used as a food supplement in Asian cuisine. This will benefit a hermit crab. Too much algae can become problematic.

Leave small amounts of bubble algae in an aquarium, but gently remove the majority by hand. Use tweezers or pliers for this, as bubble algae can be stubborn. Just make sure you do not burst it in the process.

Green Hair Algae (aka String Algae)

Hair algae is a broad church that covers many organisms that resemble green wet, matted hair in an aquarium. These algae grow and multiply quickly and can become unsightly. Many aquarium owners complain that hair algae block their view of a tank’s occupants.

Excessive iron in an aquarium is usually the cause of hair algae. Excessive light and insufficient nutrients can also lead to growth. Thankfully, most hermit crabs are keen eaters of hair algae.

All the same, you may need to step in and lend a hand. Hair algae are best removed by scrubbing them with a toothbrush. If you remove large clumps of hair algae, hermit crabs will handle the rest. The answer to “do hermit crabs eat hair algae” is a rousing yes.

Brown Algae

These algae resemble a dusting of flour. You’ll likely see them all over a tank, covering walls, substrate, and decorations. Brown algae may not look pleasant, but they are a delicacy to hermit crabs.

These algae are caused by high amounts of phosphates and silicates in a tank. It is common in newly set up aquariums. If you have plants in your aquarium, they’ll absorb these minerals and minimize growth over time; hermit crabs will eat the rest.

If they wish to remove brown algae, wipe surfaces and perform spot cleaning. These algae are the least concerning of any, though. If you’re patient, nature will take its course.

Coralline Algae

Coralline algae are usually pink, though they can be a rainbow of shades. Potential colors include red, blue, yellow, purple, white, or gray. Whatever the hue, coralline algae should be welcomed.

These algae will quickly dominate and outgrow other nuisance algae in an aquarium. Many aquarium enthusiasts actively seek out the growth of coralline algae. They look pretty, clean the water, and provide a constant, healthy food source for marine life.

Hermit crabs will typically eat coralline algae, as it’s rich in protein and tasty. If you must remove coralline algae, empty your aquarium and dissolve it with vinegar. Overall, coralline algae are a welcome presence.


Cyanobacteria are technically not algae but bacteria. All the same, cyanobacteria are commonly referred to as ‘blue-green algae’ – or, more commonly, just ‘pond scum.’

Cyanobacteria should be approached with caution. Scientific American explains that cyanobacteria contain toxins that harm humans and wildlife. Thankfully, many hermit crabs will automatically avoid eating these growths.

Typically, cyanobacteria are caused by changes in airflow or excess light. Irregular cleaning of water will also lead to cyanobacteria. As uneaten food or waste dissolves, they become bacteria.

Cyanobacteria create a musty, earthy smell. If you notice this aroma in your aquarium, watch for any signs of these bacteria. Empty your aquarium and scrape away any growth, then treat the cause.

Cyanobacteria is not all bad. Frontiers in Microbiology explains how cyanobacteria can be a useful agricultural fertilizer. If you don’t have terrestrial pets, consider applying it to your lawn for enhanced growth. Remember that cyanobacteria are toxic to animals and humans, so tread carefully.


Red Slime Algae

Red slime algae are another form of cyanobacteria. You’ll find these algae most often in strictly saltwater aquariums. Red slime algae can be invasive and unsightly, and poor water maintenance and condition will magnify growth.

Left untreated, red slime algae quickly multiply and spread, forming a layer of slime all over the aquarium. These algae are stubborn and tough to remove. Hermit crabs may eat red slime algae, but do not count on it.

Maintain an appropriate pH balance of your water to prevent red slime algae. Regularly change the water, remove uneaten food or waste, and provide a regular current. If you see the beginnings of red slime algae, remove them before they gain a foothold and multiply.

Can Hermit Crabs Survive Eating Just Algae?

A hermit crab may survive by eating algae, but surviving isn’t the same as flourishing. Don’t assume that an aquarium filled with algae is enough to keep a hermit crab healthy.

Consider the nutritional needs of a hermit crab. The most important addition to the diet is calcium. This mineral is essential to hermit crabs as it aids the development of a strong, sturdy exoskeleton. This is particularly important immediately after molting.

As per Science, hermit crabs automatically prefer shells with traces of calcium. You can buy calcium supplements from an exotic pet store or offer crushed eggshells or cuttlebone.

In addition to nutritional needs, hermit crabs prefer a varied diet. As natural scavengers, hermit crabs rarely eat the same thing twice in 24 hours. As you can imagine, sustaining itself on algae alone makes for a dull life for a hermit crab.

Vary your hermit crab’s diet. As omnivores, hermit crabs can enjoy a wide range of foods. Insects, fresh fruit and vegetables, and even small parcels of meat and fish will keep your hermit crab happy.

If your hermit crab eats algae, this is a good thing. As bottom-feeding scavengers, hermit crabs will happily consume detritus found in an aquarium, and they’ll remain contented if other foods supplement the algae. Just keep on top of spot cleaning, removing excess algae by hand.