Guide: Assassin Snails in Shrimp Tanks. Do Assassin Snails Eat Shrimp?

Assassin Snails in Shrimp Tanks. Do Assassin Snails Eat Shrimp

Actually, I would like to start off by answering the question. This question has been bothering shrimp breeders for years. There is a lot of controversy on whether assassin snails eat shrimp or not. Can it take down shrimp or not? That is because the feeding habits of this species are based on aquarium observations rather than their natural behavior in the wild.

In short, unfortunately, they do eat shrimp. So the answer is absolutely yes! Of course, it is very sad to see the death of the shrimp. Nonetheless, believe it or not, but from an ecological viewpoint that can be good for the shrimp colony. In its turn, this leads you to have a stronger better shrimp colony later on.

The point is that assassin snails will not be able to take down a strong healthy shrimp. I would like to repeat that it is highly unlikely for the snail to catch healthy shrimp. Shrimp are fast and cautious and in the moment of danger, they immediately jump away. Assassin snails are too slow for that. They have only two speeds – dead slow and stop!

If the assassin caught a shrimp I would guess it was ill, slow, genetically weak or simply too stupid and therefore must go anyway. I have never seen this happening in my own tank but I have never doubted it can happen.

Nevertheless, in most cases, shrimp breeders do not accept any risk. That is why you will not see assassin snails in the expensive shrimp tanks.

Here is the opinion of two well-known professional shrimp breeders

Marks Shrimp Tanks “I would say no. They do not kill shrimp. What does happen though is if you do not provide enough substance to them they will eventually attack your shrimp because all living organisms need food basically”.

Also, there is always a chance that assassin snails will go in“Rogue mode” and start killing shrimp.

Flip AquaticsI really do believe assassin snails will eat shrimp. I think it is extremely rare and I think it is like a great white eat a person… so if they get a taste for shrimp and they like the shrimp, they are going to continue to chase after the shrimp in and try to eat them”.

Assassine snail eat shrimpWell, I have spent countless hours searching for any information about it. I have also checked German and Russian sites and forums about shrimp. In the end, all the time, the result was the same. It can happen. Unfortunately, there is no way to know beforehand when or if it can happen at all.

So the main point with any predator is to make sure that they have access to a healthy amount of their preferred food source. If there is not enough food then they will go after the next thing on the menu. Combine it with wrong time and wrong place and we will see the reasons behind it.

Lastly, just like in the human world, you can have a crazy snail that will attack everything it can. There are aquarists who claim that assassin snails even killed some of their small fish. Well, this sounds truly fantastic. As with shrimp, the fish must be ill or half-dead anyway in my opinion.

About Assassin snail (Clea Helena)

Once I started reading about this snail, I found so much bullsh… contradictory information on the internet! Especially about breeding (like hatching period or number of laid eggs and so on). Eventually, I had to refer to rather sparse scientific articles about this species just to be sure.

Assassin Snail in Aquatic Community

These snails have become super popular in the past several years because of their ability to sort of deal with a common problem of pest snails, the Ramshorn Snails, the Malaysian trumpet snails and etc.

Assassin snail is a freshwater snail belonging to the Buccinidae family. This species can be found throughout southeast Asia, Malaysia, Thailand, and Indonesia and it is quickly taking the hobby by storm in North America, Europe, and Asia already.

Unlike some other freshwater invertebrates traded as aquarium animals, such as the shrimp Caridina multidentata (Amano shrimp) and some snails as Neritina coromandeliana, its life cycle does not include a marine stage. Thus, it is able to reproduce under aquarium conditions. But there are a few things that you should know.

Quick Stats

Parameter Optimum
Care Level Easy / Medium
Minimum Tank Size 5-10 gallons (20-45 liters)
Tank Set-Up Adaptable
Maximum Size 2.5 cm (1 inch)
Water GH 8–15
Water pH (pH) 6.2-8.2
Water temperature (ºC temperature) 22 – 28 (71 – 82F)
Hardness (mg/l of Calcium Carbonate) 100 mg/l upwards recommended aquarium maintenance range
Life span from 2 to 5 years
Diet Carnivorous
Plants No special requirements
Lighting No special requirements

Assassin snail does not live in brackish water in the wild. Although, it can tolerate slightly brackish water conditions for some time.

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Appearance and body structure of the Assassin Snails

Assassin snail body StructureThe easiest way to identify them is by the yellowish and brown bands on their shell. It conforms to its family in terms of shape, having a tightly coiled shell with moderately deep radial ribs and one, two, or three brown spiral bands.

Maximum length is around 30 mm but usually smaller (20 mm or 0,8 inch). In particular, the apical part of the shell is often worn away on older snails. There is an obvious siphonal notch through which the siphon protrudes the operculum (trapdoor) is brown. Adults and juveniles look very similar, except that juveniles are paler in color.

The assassin snail possesses a relatively thin and translucent muscular foot. As well as head bearing a pair of mobile, partially retractable, tentacles with eyes near the base.

Nobody knows about their ability to see. Do they rely on sight during hunting at all? Researchers suppose that most likely they can only see differences between light and dark.

 Numerous sources have described the assassin snail’s ability to detect food items at a distance through the tentacles. Their robust siphon functions as a versatile water sampling extension. The siphon, formed from an extended fold of the left mantle edge, also functions as a snorkel (breathing tube) when the assassin snail is buried.Sssassin snail without shell

The foot: the propodium, is extremely mobile and plays a role in climbing, burrowing, and food capture and handling. While the mesopodium provides a large ventral surface area for pedal locomotion and the metapodium bears the operculum.

The operculum acts like a trapdoor to shut off the shell when the snail is hiding inside.

The shells of the assassin snails are thinner than those of similar sized marine snails but they are quite robust in comparison with other freshwater snails.

Typical Behavior of the Assassin Snails

Assassin snail activity timeI have read in many articles that these snails are mostly nocturnal and during the day they will bury themselves within the substrate.

This is not completely true.

Some studies showed that their behavior does not change much depending on the daytime. They are relatively active during any time.

Another interesting fact, as I have already mentioned, is that these snails can sense the food. Once the snail’s activity was at its lowest, the researchers added staple food (tropical fish flakes). It caused a rapid increase in the level of the snails foraging activity.

A similar effect, slightly muted in intensity but extended in duration, was when they added a small, live planorbid snail as supplemental food.

Clea Helena is a burrowing species and does best in tanks with a sandy or soil substrate.

If nothing else, this gives the aquarist an opportunity to watch the natural behavior of the species. It is also more likely to reproduce successfully in a tank with a sandy substrate since the juvenile snails seem to spend a lot of time hidden underground.

Note: actually, they will be OK even in a tank with larger gravel particles, in which they can also breed without problems.

Assassin Snails: Hunting and Eating

Assassine snail huntingClea Helena is opportunistic carnivores that feed on both live prey and carrion. Assassin snails use two ways to catch the prey.

One of them is an ambush tactic. They borrow underneath the substrate and wait until their prey comes close enough. Then they “quickly” jump into action. Another one is to run crawl and catch. Assassin snails “rapidly” pursue their prey, subduing it with their foot before devouring them through the aperture.

I have read that the Assassin snail emits some kind of toxin that immobilizes their prey, and then they feed on the hapless prey. I tried my best to find scientific proof but could not verify that.

You can often see them cruising around with proboscis extended hunting for food. When they feed they use a fork-like appendage that they extend into the cavity of the snail. Then they suck the body of the snail out while it is still alive. Frankly saying, it does not look nice at all.

Note: In some cases (Ramshorn Snail) you can see actual blood trails. The common Ramshorn snail has red blood, because, like humans, it has hemoglobin (which uses iron instead of copper) in its blood cells. The picture is nasty.

So what they do is they grip the snail with their foot or the bottom. Then they jab this proboscis (fork-like appendage) into the body of the snail eating it out. It seems to use that proboscis and then its own foot to peel open the other snail’s trapdoor.

Interesting fact:

There is no safe snail for assassin snail. Some people think that they will not be able to kill big snails like Mystery snail or Ampullariidae snail. Let me disappoint you. They can and they will. If these snails are interested in attacking a larger snail, they will gang up together and take it down in force. It is pretty gnarly.

My assassin snail does not eat pest snails!

Sometimes people start complaining that they bought assassin snails and they do not do anything. Nothing seemed to happen. There can be several reasons for that:

  1. If they are breeding without eating the snails then they are getting too much food elsewhere. Feed them less. Make them work for it. Be patient and they will do their job.
  2. Also, if your tank is swarming with pest snails, do not expect them to eliminate all snail in a week or two. They are not troglodytes and cannot eat all the time. Eventually, you will notice the overall snail population dropping a bit.
  3. Pest snails are too small. It sounds strange but they seem to ignore anything smaller than 1/10th of their size or so. Maybe because they proboscis cannot enter into the cavity of the small snails.
  4. You have added a small number of assassin snails and all of them are females or males. There is a hypothesis that in order to “work” well they need an incentive. The prime incentive is a reproduction, which takes a lot of energy. If they do not reproduce, their appetite is low.

If you run out of pest snails

Once all of your pest snails are gone within your aquarium, assassin snails will move over and eat fish food as well. Therefore, if you run out of pest snails in your shrimp tank, you can also give them fish or shrimp pellets/ granules, white mosquito larvae, or meaty food like bloodworms, etc.

Nonetheless, keep in mind that they breed most prolifically with a live diet.
Note: something to remember is that an assassin snail would rather die than eat another assassin snail. They do not prey on each other and will starve to death before they will eat their own kind.

Do Assassin Snail Eat Planaria?

There is a popular rumor that this snail can also get rid your aquarium of planaria. That would be great news for any shrimp breeder. I have no idea how this myth was born but I could not find a single proof for that. Therefore, in my opinion, this statement is straight up misinformation.

Just look at this video and you will see that it will be very problematic to catch the planaria and eat it on a regular basis. Maybe once a year, I guess.

Reproduction of the Assassin snails

Assassin snails are not hermaphroditic like many other snails. They are sexual (male or female). The problem is that it is basically impossible to distinguish sex. Both, males and females seem to have the same shape, size, and coloration.

Therefore, if you are planning to breed them, you need at least 6 – 8 snails to ensure you have both sexes.

Assassin snails can breed in captivity. Depending on aquarium conditions, they reach sexual maturity in 6 to 8 months when they are about 1 cm. They do not breed fast, compared to other snails. On the contrary, it takes some time. So you should not worry about overpopulation any time soon.

Mating process of the Assassin Snails

Assassine snail matingUnder aquarium conditions, snails mate above the surface of the substrate. Pairs or groups of snails clamber over each other, lock together, and remain in close proximity for hours. According to research, copulation usually lasts for 3 h 40 min ± 45 min.

Sometimes sated pairs can be foraging together for a period of many days. In addition, mating activity may occur communally. Eventually, the males and females separate, and the females go off to lay their eggs.

Laying eggs

Assassin snail egg developmentAfter mating the females then go and lay the eggs on a hard surface (for example, driftwood, rocks, glass or plant stems) presumably as a protective mechanism.

Each female deposits between 1 to 4 eggs per clutch in a straight line, separated from each other by 5 mm approximately. The diameter of the egg is about 400−570 μm.

Note: The eggs are very tiny and it can be difficult to see them. They look like little envelopes. There are numerous cases than people bought plants from different shops and they have come with assassin snail eggs. As a result, they accidentally introduce assassins to their aquariums.

Eggs look like capsules that are square in shape and approximately 1.0 to 1.5 mm in width and length, with convex sides slightly larger than the enclosed egg.

They look white-yellowish to the naked eye but are nearly transparent. After a few days, the white-yellowish egg will turn light brown.

The Effect of Temperature on Hatching

The snails hatch in 46-58 days. Egg development is accelerated with increasing temperature. They also stop breeding if the temperature reaches 20C. Over this period, the embryo undergoes complete non-feeding, benthic development to hatch as a crawl-away juvenile.

The hatching process seems to involve the dissolution or splitting of a “mucoid plug” or “seam” at the top of the capsule.

Hatching and development of young snails are imperfectly known. Nonetheless, according to observations, the juveniles hide in the substrate almost all the time feeding on whatever small organisms they find there.

Newly hatched juveniles are about 3.1 ± 0.3 mm and resemble the adults in shell shape and color although typical shell stripes are not clearly marked. They burrow until their shells harden and usually start showing up once they are about six months old by which time they have a shell length of around 8 mm.

Breeding Assassin Snails in Aquarium Conditions. Maintenance

It is easy and difficult at the same time. On the one hand, assassin snails do not require much. They are very undemanding.  Some breeders do not even use filtration in the assassin snail tanks.

On the other hand, they do reproduce really slowly! Also, being carnivorous means an aquarium of a given size will support a much smaller population of Clea Helena than omnivorous or herbivorous snails. Generally, it will take several months before you can get first baby snails.

Calcium is important for maintaining a hard shell. They should get this from their diet, but you can add calcium supplements to the water if they are not getting enough.

I highly recommend reading my article “How to Supplement Shrimp and Snails with Calcium”.

Note: It would be better to cover the aquarium to reduce the likelihood of their escaping or getting injured or killed while trying.

Assassin Snail and Pest Snails Control

As I have already mentioned these snails can be really valuable for dealing with pest snails problem. You will not have to wait because assassin snails will usually go right after them. They do not waste any time.

There are many of us that like to house decorative snails. If you keep assassin snails in your display tanks or especially planted ones and decide to share decorations, plants, or anything else it is very easy to transfer the eggs to another aquarium. Be careful that you do not accidentally transfer assassin eggs into your tanks that will house ornamental snails.

Common Assassin Snail Tank Mates

Well, almost all articles about snails, shrimp or fish also describe the good and bad tank mates for them. So I feel obliged to do it as well.
Obviously, it is not possible to keep assassin snails with other snails like Nerite snailsMalaysian Trumpet SnailsRamshorn Snails, etc.

Regarding the fish, well, because this blog is about shrimp I can recommend reading my article  “Сherry Shrimp in a Community Tank. Tips to Make it Successful”. If the fish is good for the shrimp it will be also safe for the assassin snail.

The same is with dangerous fish. Clea Helena is vulnerable to predation when kept with large fish. Cichlids, pufferfish, loaches, and certain catfish are likely to view the snail as potential food.

In Conclusion

Many shrimp breeders have assassin snails in the shrimp tanks.

Yes, they do eat shrimp.
No, they do not do that very often. It is a very rare case. They cannot prey on anything that swims faster than they move. So shrimp, who are healthy, are in no danger from assassin snails.
No, I would not put assassin snails in my expensive shrimp tank anyway.

These snails can be really great for taking care of the pest snail problem. These little guys are really sturdy and tolerant to a wide range of parameters. Assassin snails can be a great addition to the community tank.

Related articles:

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17 thoughts on “Guide: Assassin Snails in Shrimp Tanks. Do Assassin Snails Eat Shrimp?

  1. I turned my fish tank on this morning and found two Assassins eating one of my Dream Blue Shrimp! Also a baby Assassin was hitching a ride on the back of one of my Nerite Snails! I have 3 adult Assissins and have counted 5 tiny baby ones. Also I have 9 Nerites. I have not lost a Nerite yet! Been about a year now. Great article to read 🙂

  2. The rumor of them predating on planaria & other small aquatic worms refers to the diet of the substrate dwelling juveniles, not the larger adults.
    While they are confirmed as a facultative vermivore, their slow reproduction rate still makes them less than ideal for planaria control in aquaria.

    1. Hi Aquatic Theory,
      I absolutely agree with you.
      There are no proofs that Assassin snails hunt for planaria. In my opinion, this is a myth.
      Best regards,

  3. Will shrimps eat on the assassins snail eggs? Can you breed them both in the same tank?

    1. Hi Cristian,
      No, shrimp will not eat assassins snail eggs. I would not worry about that at all.
      Yes, you can breed both of them in the same tank.
      Best regards,

  4. I actually threw my helena out of my shrimp aquarium (to my other aquarium) because she got a taste for shrimp.
    But she actually developed a hunting tactic on them.
    She would burrow under the sand and strike when a shrimp came by, then pull the shrimp under the sand. First time I saw it, I didn’t believe it. The second time I intervened after she had killed one of my pregnant female shrimp. I have high quality blue dreams, so they are a bit too expensive food for that snail.
    Never an assassin snail again. I’ll find another way to get rid of the pests….

    1. Hi Aritcia,
      I’m really sorry to hear that. It is very strange that shrimp did not react fast enough.
      Nonetheless, thank you for the feedback.
      Best regards,

  5. Hi I just got a two assassin snail with my shrimp tank and I’m wondering if I should separate them I haven’t noticed anything but I don’t want to lose a mystery snails or a bunch shrimp but I like the assassin’s snail but I don’t want to lose more then what I got what your apend on that?

    1. Hi Tom,
      Although assassin snails may catch shrimp, it is extremely rare! So, I would not worry about losing a bunch of shrimp.
      On the contrary, your mystery snail is not in safe place. There will always be a risk of aggression.
      Best regards,

  6. I came to this website cuz I literally just woke up, checked on my aquarium and saw an assassin snail chomping down on a juvinie ghost shrimp while its legs twiched.

    So yes, they do eat shrimp.

      It is true. Sometimes it may happen.
      Thank you for the feedback.
      Best regards,

  7. When we first started with assassin snails we had them with our high grade blue shrimp. Never had an issue.
    What we did notice is that after the eggs started hatching, a few days later all the limpets were gone. We had a ridiculous amount of fresh water limpets in our tank, so when they disappeared it was very obvious.
    We are tempred to deduce that baby assassins are skilled limpet hunters with an apetite that knows no end.
    Now we have 2 tanks that are over running with helena snails (we really love them), and we tried to add some culled shrimp with them, but… we never saw them again up to this day…
    Maybe an overwhelming number in assassin snails produce a different hunting patern? Or just that one assassin will eventually catch a shrimp at some point, but given that there are many, the “not so probable” event of shrimp being captured turned out to be very probable.

    1. Hi Victor,
      Thank you for sharing your experience.
      Best regards,

  8. I get a lot of assassin snail eggs, but they seem to disappear or empty out well ahead of the amount of time it takes to hatch. The only other inhabitants in the tank are cherry shrimp. Any idea what’s happening to the eggs?

    1. Hi Infolific,
      Tell me, how many snails do you have in your aquarium? If the eggs weren’t fertilized, they won’t develop and eventually might just decompose in the tank. In that case, if something is rotting and decomposing, the shrimp will eat it.
      Best regards,

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