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Wednesday, March 9, 2011

Assassin Snails

By Paul Michael Van Langen
An attractive and colorful snail that won’t eat plants and will help to control the population of undesirable snails in your tank sounds a bit too good to be true, but that’s exactly what many aquarium hobbyists have found in Clea Helena, commonly known and sold as the Assassin Snail or Snail-eating Snail.

Assassin Snails are whelks; most whelks are marine snails. However, the Assassin Snail is a true freshwater snail. Most snails in the Clea genus prefer fast-moving clear streams. Clea Helena is unique among its genus in the fact that it is found in more stagnant bodies of water like ponds and ditches, and is therefore more tolerant of a wider range of water conditions and quality. This probably accounts for it's popularity.

Although there are many other snails in the genus, more often than not a snail sold in a store under the name Assassin or Snail-eating Snail will be Clea Helena.

Assassin snails, like many other whelks are both active predators and scavengers. They will eat meaty detritus as well as hunt down other snails. A favorite prey for them seems to be softer shelled snails like pond snails (a common nuisance snail in the aquarium). They will also eat MTS (Malaysian Trumpet Snails) and other small nuisance snails. They seem to try and “hunt” Ghost Shrimp and Amano Shrimp on occasion, although I have never seen them catch one. I imagine that a shrimp would have to already be half dead to fall prey to an Assassin Snail.

The Assassins are safe for community tanks although they will likely go after any small fry or eggs left unprotected.

I have also had some success with them in semi-aggressive tanks with medium to small fish, they have a relatively tough shell and can survive some assault. Although a constant assault would keep them from eating and if the fish are this aggressive towards snails it is likely the tank will not have a snail problem to begin with.

I would not recommend housing them with any loaches or other fish known to eat snails, or any fish large enough to swallow them whole; this could be quite problematic because of their tough shell, and some fish like Oscars will eat anything they can swallow.

They are also safe to keep with other larger snails; they typically will not go after something much larger than themselves so Apple Snails and Mystery Snails are usually safe tank mates although any eggs may be eaten.

Assassin snails are fairly tolerant of water quality issues compared to other snails in their genus but don’t make the mistake of thinking they are as hardy as something like a Mystery Snail. They are not air breathing snails like many other aquarium snails, and are therefore more sensitive to water quality issues as well as oxygen content in the water.

Although they are freshwater snails, they will tolerate some salt, and it is reported they will tolerate brackish water and can be successfully kept in a brackish aquarium.

Aim for a PH of around 7-8,although anything from 6-8 is likely fine. Slightly harder water is preferred, but I have seen these snails kept in a variety oftanks successfully. They prefer a substrate of fine sand or at least finer than pea gravel; much of their time is spent burrowing in the substrate.

As with other inverts, be very carefulusing medications with copper (Don’t use them!), this will more than likely kill them. If anything in your tank absolutely needs to be medicated with something containing copper, remove that item and treat it separately.

Feeding these snails is very simple. If you have an unwanted snail problem in your tank, the right amount of Assassin Snails will develop a balance, and feed themselves. Otherwise, they are proficient scavengers, and will eat left over fish food, etc.

If you are worried your assassin snails may not be eating enough, a few shrimp pellets, or other sinking meaty foods put in the tank at night can help supplement their diet. I recommend getting 1-2 Assassin Snails to start with and observing the effect they have on your tank and/or the snail problem you have. This way you can get an idea of how much they consume and decide how many you want. In a smaller tank 1-2 may suffice.

If you want assassin snails just for the aquarium and do not have a snail problem, wait until the tank has matured for a few months before adding them.

It is not recommended to add Assassin Snails to an un-established tank because they are more sensitive than other snails.

They can be fed as mentioned above with sinking meaty type foods in the absence of any snails to prey on, and are a quite nice addition to any tank in their own right so don’t think you have to have a snail problem to get a few!

Assassin Snails are still a fairly recent introduction to the hobby, so they may not be available in some pet stores; many of the large chain stores still do not commonly carry them, so you mayhave to go a bit out of your way to get some for yourself.

Fortunately even if you are weary about ordering fish online Assassin Snails are quite a safe bet as they will survive much longer in a shipping bag than a typical fish or many other inverts would.

It is possible that they will eat their own kind if they are very hungry, and some people have reported finding empty shells in a shipment. However, it is much more likely the other snails were eaten after perishing on their own. I have never seen an assassin snail attack one of it's own kind.

So if you have a snail problem, or you’re just interested in a unique looking snail that won’t harm your plants, Assassin Snails just might fit your needs. They’re a colorful addition to any tank and although they spend a good bit of time burrowing, I find mine are often visible hunting and eating other snails during the day. It’s fun to watch them track other snails and it’s rather amazing the amount they can actually consume.

They’re a great way to control an undesirable snail problem. They may not immediately kill every undesirable snail in a heavily infested tank, but they will take care of the problem.

In my opinion, Assassin snails are the best way to control an unwanted snail infestation in a natural way that poses no risk to your aquarium. A bad infestation can even be controlled by using traps in conjunction with Assassin Snails, just pick the Assassins out and put them back in the tank when you remove the trap. You can also save a few of the trapped snails to feed your Assassins later.

Nixon, A. (2008). Assassin Snails and Sulawesi Elephant Snails: Keeping Clea and Tylomelania in the aquarium. Conscientious Aquarist Magazine. Accessed at

Sounguru. Assassin Snails A Little About Them. Aquatic Community Aquarium Forums. Accessed at: