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Planarian worms have been a source of frustration for aquarists for many years. If you spend enough time practicing this hobby, you’ll bump into these critters at some point.

But that doesn’t mean you’re stuck with them.

This guide will cover what planarian worms are, and how you can get rid of them.

What Are Planaria Worms?

Do you find yourself dealing with a dreaded planaria infestation? Congratulations: You’re a true aquarist!

Planarian worms are an incredibly common frustration for those who partake in this hobby. Ask any experienced fish keeper, and they’re likely well acquainted with this unique pest.

A planarian worm (planaria is the plural form) is a flatworm. Contrary to popular belief, it’s not strictly parasitic. It indeed exhibits parasitic behavior, but these little guys can survive on their own in your fish tank.

Fully grown, planaria are very small. Most are a mere 10 millimeters long. The lucky ones can surpass half an inch. However, most are small and difficult to observe.

You might see a stray planarian gripping the glass. But most aquarists don’t realize that these worms exist until they become a significant problem.

If you’re lucky enough to get close, many distinct features are worth observing. Planaria are often misidentified as other common flatworms. But these pests have many distinctive traits.

The first is their angled head. A planarian’s head is arrow-like in shape. The only time it’s not is when it compacts itself for movement.

Look even closer; you’ll notice that planarian worms have tiny, beady, cross eyes.

There are a few different kinds of planarian worms. The worms can take on the color of whatever they eat, but the two most common varieties that live in fish tanks are white and black/brown.

How Do They End Up In Your Fish Tank?

When newer fish keepers see these critters wriggling around the tank, many will go into panic mode. Seeing living pests show up out of nowhere in an enclosed environment is alarming.

So, how did they get in your aquarium?

It’s easier for these worms to get around than most realize. To make matters worse, you might have been the one to introduce them into your tank! Here are a few common ways planarian worms get into tanks and flourish.

Parasitic Hitchhiking

Ever wonder why experienced aquarists tell you to quarantine new tank additions? Perhaps you’ve wondered why so many stress the importance of sanitation and thoroughly rinsing. While there are countless reasons to be wary of what you add to your aquarium, planarian worms are one of the common issues that can occur when you don’t do those things!

You see, these pests are master hitchhikers. They are tiny enough to hide and travel on a wide variety of objects. They often get added to fish tanks by way of live plants. 

Some types of planaria feed on plant detritus and biofilm, making live plants the perfect source of food. When you add the plants to your tank without taking extra sanitary measures, you may inadvertently introduce the worm and spark a significant problem.

All it takes is one worm (more on that in a minute).

The pests also frequently slip into rock crevices and voids in driftwood. The pest can even hide in plastic decor. Always take steps to prevent contaminating your tank and make sure everything you add is worm-free

That includes new fish as well. Planaria can also hitchhike on fish and inverts!

Infested Substrate Or Filter Media

In many cases, planarian worms get into tanks through filter media or substrate. It’s not uncommon to move things around and inadvertently spread these pests. Perhaps you’re using substrate from one tank to create a smaller breeding tank.

Or maybe you’re using filter media to speed up the ammonia cycle. Whatever the case might be, there are many risks. Planarian worms love to eat waste and detritus that ends up in the substrate. Loose material like gravel is particularly risky as these worms can wriggle their way into the voids to avoid capture.

Like before, always clean and sanitize additions to prevent infestation problems.

Asexual Reproduction

Having a single planarian in your aquarium doesn’t seem like a huge deal. But that’s all it takes to start a substantial infestation!

Author Note: Planarian worms reproduce asexually. That means that they don’t need male and female specimens. If the conditions are right and there’s ample food around, it’s only a matter of time before these worms take over.

Here’s another interesting fact: An injured planarian can heal itself and create additional worms!

It’s a fascinating evolutionary trait that makes getting rid of the pest a nightmare. Say that you find a sole planarian and squish it with some tongs. Instead of killing it, you break it apart into multiple pieces.

Those pieces will slowly heal, creating multiple new worms from the one! The cycle can continue the more you attempt to kill the worm physically. Pair that with quick asexual reproduction, and it’s not hard to see how infestations get out of hand.

An Abundance Of Food

Of course, having an abundance of food is a quick way to see a minor problem turn into a major one. Planarian worms are relatively common in the world of fish-keeping. Aquarists have to deal with them at some point.

Usually, they’re not a significant issue. We’ll get into it when they are in a bit, but the worms don’t cause much harm for the most part.

But when the population flourishes to the point where you see little swarms of worms, you have a problem. Usually, this occurs because of an overabundance of food available to the pests.

The black and brown-colored worms typically thrive in the presence of waste. That can be waste from fish in the tanks, plant detritus, and leftover food. It could indicate that you have a filtration problem or the bioload of the aquarium inhabitants is too high.

White planarian worms typically eat living things. They usually feed on the tiniest microorganisms residing in the tank. That includes microscopic worms, daphnia, bloodworms, etc.

Should You Be Worried About Them?

Whether or not planarian worms are dangerous depends on what type of aquatic creatures you’re keeping.

If you have nothing but fish, these pests are relatively harmless. In fact, some species of fish will find the worms to be tasty snacks! But if you’re keeping invertebrates like shrimp and snails? That’s when planaria become downright lethal.

These seemingly innocent worms can cause immediate harm to shrimp and snails. White planaria will hunt down shrimp and snail eggs. They feed on tiny baby shrimp and can also go after adults if they’re big enough.

Planaria are devastating for dwarf shrimp species.

Black and brown planaria don’t eat your shrimp and snails directly, but they have other means to kill them.

These worms move on slime trails, much like snails. However, the worms’ trail contains a toxin that will stun and paralyze any shrimp or snail touching it. That gives the planaria free reign to eat your precious inverts alive!

They get under the exoskeleton and devour shrimp. With a large population of planaria, it doesn’t take long for that to happen.

How To Get Rid Of Planarian Worms

Getting rid of planarian worms is no easy task. All it takes is a single planarian to kickstart a thriving population. As a result, you must eliminate every worm to address the issue effectively.

That’s a tall order, but here are tips to help you manage this pest problem.

1. Planaria Worm Traps

This trick is more of a control technique than an extermination method. As mentioned earlier, planarian worms aren’t dangerous for every tank. It all depends on the type of creatures inhabiting it.

If the worms’ presence isn’t life-threatening, control methods are a great way to keep the population under control without going to potentially stressing extremes.

A planaria trap is a simple device. It’s typically made of glass and allows you to regularly catch and physically get rid of worms. All you have to do is add a piece of bait. Bloodworms, meat, mosquito larvae, and any other high-protein food will do.

Place the trap in the water and allow the worms to get trapped before removing them.

2. Medicated Tank Dewormers

Deworming medications contain similar ingredients to a cat or dog dewormer. The concept is simple: Add the drug to the tank and let the chemical elements work their magic to kill the planarian worms. If you’ve ever treated the habitat for Ich or other common pet issues, you won’t have any problems.

But here’s the thing: There are risks. Medications usually contain active ingredients like flubendazole or fenbendazole. Those chemicals can kill snails and cause unwanted stress for other inhabitants.

Some snails will survive, but others will not. The best action is to create a quarantine tank in which the snails can live for several months. Those active ingredients take a long time to get filtered out of an aquarium, so they’ll be separated for a while.

The good news is that medications are very effective at killing these worms. Repeat the treatment two weeks after the initial one, and your aquarium should be planaria-free!

3. Introduce Predatory Tank Mates

Here’s another way to control the planaria population without using chemicals. As we mentioned earlier, some fish species love to eat these little pests! Use that to your advantage and try introducing some to the aquarium.

Good planarian-eating fish species include:

Add a good number of these fish to your tank, and it’s terrible news for any planaria in the tank!

4. Proper Disposal

Your job doesn’t stop after you get rid of planarian worms. Whatever you do, don’t dispose of these guys down your drain! Remember: They multiply quickly and can heal to create new worms after injury.

Simply dumping the worms down the drain can cause unnecessary stress on your city’s water system.

Many aquarists prefer to boil or freeze the worms. No part of the worm will survive this process, ensuring they’re completely dead before disposal.

Ways To Stop Them From Coming Back

The best thing you can do to avoid planaria issues in the future is to be vigilant about keeping your tank clean.

Of course, take precautions when introducing new decor into your aquarium. Go through all the necessary steps to sanitize plants and rocks, and do your best to avoid introducing worms into your underwater ecosystem.

That said, keeping your fish tank clean with regular maintenance is one of the best ways to avoid infestations. If you deprive the worms of what they need to survive, those stray planarian worms that get added won’t have the means to multiply.

Make a habit of cleaning your substrate and filter medium. Siphon up waste and don’t let things accumulate at the bottom of the tank.

Be mindful of the food you feed, too. This is especially important if you have shrimp. Leftover waste is like a buffet for planaria, so remove any uneaten morsels to prevent trouble.

Keep an eye on your feeding cycles. Whether you’re providing food to shrimp, fish, or both, be mindful about how much you’re offering. Fine-tune meal sizes to leave as little waste on the bottom of the tank as possible.

Conclusion

Now that you know the proper way to get rid of planarian worms, it’s time to take action. Assess the current situation in your tank and select the appropriate method.

And as always, if you have questions don’t hesitate to ask!