Assassin Snail – Detailed Guide: Care, Diet, and Breeding

Assassin snails (Clea Helena) are one of the most common snails in aquarium hobby these days. Their increasing popularity as aquarium pets should not be a surprise, though. They are often sold in the aquarium trade as a biological agent intended for controlling the aquarium overgrowing by other pest snails (like Bladder snails, Pond snails, Ramshorn Snails, and Malaysian Trumpet Snails).

Assassin snails are carnivorous in their feeding habits. They feed on live and decaying organisms, including worms and other snails. They are pretty hardy and easy to keep, making it a good snail for beginners.

Just a little remark before I begin: In my research about these snails, I was really surprised to find out how little known about Assassin snails in science. Even more, the researchers stated that virtually nothing is known about this species’ natural life traits. Much of what is currently known about the species is based on aquarium observations. What a surprise! Basically, our hobby is almost ahead of science.

Nonetheless, if you are thinking of keeping Assassin snails in your aquarium, or simply want to learn more about this species, you have come to the right place. I have gathered all information about this species based on existing studies, experiments, researches, and experience of aquarists.

This complete care guide for Assassin snail (Clea Helena) covers all aspects, from natural habitat conditions and how they should be cared within your aquarium, to dietary requirements and how to breed them.

Quick Notes about Assassin snails

Name	Assassin snail
Other Names	Snail eating snail, Bumblebee snail
Scientific Name	Clea Helena /  Anentome Helena
Tank size (optimal)	10 gallons (~40 liters)
Keeping	Easy
Breeding	Medium
Size	2.5 – 3 cm (~1 inch)
Optimal Temperature	24 – 28 C (75 – 82F)
Water type	Freshwater
Optimal PH	7.0 – 8.0
Optimal KH	2 – 10
Optimal GH	6 – 20
Nitrate	Less than 20 ppm
Diet	Carnivorous
Temperament	Peaceful
Life span	up to 5 years
Color Form	Yellow and black bands

Origins, Natural Habitat of the Assassin snails

Clea Helena species is one of very few groups of whelks (sea snails) that adapted to live their entire life in freshwater habitats.

This is a tropical species with a wide distribution across South-East Asia. Tropical rainforest and tropical monsoon climates as preferred climates for these snails.

Clea Helena is very commonly seen in the waters of Java, Indonesia, Cambodia, Vietnam, Lao, northern Peninsular Malaysia. In Thailand, Assassin snails can be found in all regions.

Clea Helena species lives in a variety of freshwater habitats, typically in places with a soft substrate.  In the wild, they can be found in standing and moving freshwaters such as streams, rivers, lakes, ponds, canals, ditches, agricultural water sources, and reservoirs. 

Description of the Assassin snails

Assassin snails are easily one of the most recognizable snails in the aquarium hobby. Their bright yellow and dark brown banded trumpet shells will definitely draw attention!

They have typical ovate-conical shells that usually grow up to 3 cm (1.3 inches) but usually smaller (2.5 cm or 1 inch). The apical part of the shell is often worn away on older snails.

Their shells are thick and have 5 – 6 whorls spiral with lateral ridges and a brown operculum (the trap-door). The operculum is the other part of their structure and is the place utilized to close the shell’s opening. This is a nice way to see whether your snail is healthy and alive. The operculum falls off as soon as the snail dies but will not close properly if there is something wrong with the snail.

The body of Assassin snail is yellowish with grey speckles all over. The mantle forms a foldable tube, while the siphon is equipped with chemoreceptors, that like in other predators or scavenger species. They use it to perceive water and locate food at a distance.

Their robust siphon functions as a versatile water sampling extension. The siphon, formed from an extended fold of the left mantle edge, it also functions as a snorkel (breathing tube) when the assassin snail is buried.

The Assassin snails possess a relatively thin and translucent muscular foot (the propodium). The foot is pretty mobile and plays a role in climbing, burrowing, and food capture.

Their heads have a pair of mobile, partially retractable, tentacles with eyes near the base. However, there is still no official data regarding their ability to see. Researchers mostly presume that Assassin snails are only able to see the difference between light and dark and they do not rely on sight during hunting.

In aquariums, Assassin snail can live up to 5 years under optimal conditions.

Related articles:

• Snails External Anatomy
• Snails Internal Anatomy

The Behavior of the Assassin snails

Although Assassin snails are considered nocturnal (active at night and bury themselves during the day time) this is not absolutely true.

Results of the experiment showed that Assassin snails’ activity decreased only a little bit compared to night time. A mere fact that this specie bury during the day time does not mean that they are sleeping or resting. It is just the way they act and hunt.

Assassin snails have very sensitive receptors in the siphon that allow them to perceive water and locate food. According to another experiment, when researchers added protein food it immediately caused a rapid increase in the level of the snails foraging activity. Almost the same was the reaction when they sensed a potential prey (planorbid snail) nearby.

They are not social and will be perfectly fine by themselves. However, Assassin snails do not hesitate to team up if they are interested in attacking large snails.

Generally, Assassin snails are not aggressive towards each other. However, in one study I read that they can attack smaller snails of their own species if they are very hungry and do not sense other food around.

Note: I have never witnessed anything like that before. It looks like they must be absolutely desperate. Personally, I believe that they will not attack another Assassin snail unless it is dying. Maybe that was the case. 

Feeding Assassin snails

Assassin snails are carnivorous (scavengers and predators). They do not eat algae. They eat dead organisms and consume meaty leftovers. If the prey is not strong enough to escape and/or fight back, they can feed on live organisms (including worms and other snails) as well.

Assassin snails thrive on a high-protein diet. Therefore, if your aquarium cannot provide sufficient food, you have to supplement their diet. For example, you can feed them (links to check the price on Amazon):

• Frozen blood worms,
• Mysis shrimp
• Brine shrimp,
• Hikari Sinking Carnivore Pellets,
• Fish food flakes,
• TetraMin Plus Tropical Flakes

There are varieties of flakes, pellets, wafers, and freeze-dried meals you can get from pet stores, and usually, you can just choose whatever food is most appropriate for the fish that share the aquarium with them. 

Calcium is vital for good shell growth. Therefore. I highly recommend reading my article “How to Supplement Shrimp and Snails with Calcium”.

Hunting styles of Assassin Snails

Depending on how hungry they are, their hunting methods can vary from active hunting to patient waiting (an ambush tactic).

When Assassin snails are not hungry, they often bury in the substrate as a precaution against potential predators (for example fish, crayfish, crabs).

They can spend underneath the substrate several hours before they start feeling hunger. So, when other snails come close enough, they may attack.

You can often see Assassin snails cruising around the perimeter of their tank with proboscis extended hunting for food. Once they get to their prey (the snail), they hold it with their foot and use the proboscis (fork-like appendage) to suck the body of the snail out while it is still alive.

Some people say that Assassin snails use some kind of toxins that immobilizes their prey. Actually, I have not found any scientific proof to verify that. There is no a single study that mentions any kind of venom or toxin in the biology of this species.

Assassin snails do not need toxins, they are pretty strong snails and can overpower other snails with their strength. Even snails that have trapdoors are not completely safe. Assassin snails use their proboscis to peel open the other snail’s trapdoor.

Experiments: Assassin Snails vs Pest Snails

It is a well-known fact that Assassin snails became very popular among aquarists because they have a reputation of being able to keep populations of some other freshwater snails under control.

Their voracious and non-selective appetite for living snails, as well as carrion, will work really well for any tank. Therefore, Assassin snails are strongly recommended as one of the safest and easiest ways to fix this problem.

You can read more about it in my article “How to Remove Snails from a Shrimp Tank”.

However, are Assassin snails really that effective? How fast can they eat other snails? How many snails do we need in our tanks for that? Are there ways to improve their efficiency?

Like many of you, I would like to have numbers! I do not want to hear these general explanations.

Unfortunately, most care guides repeat the same information without details. But not on my blog! I have found several studies where researchers conducted experiments for many weeks and months.

First experiment:

The experiment with Clea Helena involved 10 adult predatory snails, which were planted in an aquarium with 100 Malaysian Trumpet snails and the Quilted Melania. In order to test the range of nutrition for Assassin snails, after the first week of the experiment, artificial and natural forages were added to the model aquarium.

• First week: 10 Assassin snails consumed 38 pest snails (Basically, 1 pest snail in 2 days).
• Second week: 10 Assassin snails consumed 25 pest snails (Basically, 1 pest snail in 3 days).

The third and fourth weeks of the experiment showed that with the accumulation of organic matter in the aquarium, there was a decrease in the activity of snails` nutrition.

Second experiment:

The result showed that Assassin snails can consume per week:

• 6 – 11 Indoplanorbis sp (1 – 2 snails per day).
• 11 – 23 Bladder snails (Physella ) (2 – 3 snails per day).

As we can see, the bigger the prey the fewer snails Assassin snails will eat.

• Malaysian Trumpet snails (2 – 4 cm or 0.8 – 1.5 inches)
• Indoplanorbis snails (2 – 2.5 cm or 0.8 – 1 inch)
• Bladder snails (5 cm or 0.6 inches)

Are Assassin Snails Plant Safe?

Yes, Assassin snails are absolutely plant safe. They will not even touch any plant in the tank. They simply do not eat any living plant material.

Keeping and Caring for Assassin Snails

These snails are hardy by nature. Assassin snails are found in ponds, small streams, waterfalls, and ditches, and has a tolerance for a wide range of water conditions. However, they still have some specific requirements if you want to create an ideal environment for them.

Make sure the tank has fully cycled before introducing them.

Tank size

The minimum recommended tank size for Assassin snails is a 5-gallon (20-liter) tank. Bigger tanks have a greater capacity to absorb sudden water changes and shifts than smaller tanks do.

In addition, the bigger the tank, the better it may be to setup with diverse areas for them to dwell.
Tip: Although Assassin snails are not escape artists like some other snails are, its best to keep the tank covered.

Water parameters:

Assassin snails are not very fussy about water parameters. Try to aim for a pH between 7.0 – 8.0 with moderate to high KH and GH levels (8 – 20).

The water should ideally not be too soft and/or acidic, as this could lead to deterioration of the shell. This is a general rule for all snails.

Note: Snail shells are comprised of 95–99.9% calcium carbonate. Low pH levels dissolve the available calcium carbonate in their shells, which leave the snails open to harm from fish.

Although Assassin snails can tolerate pH 6.5, it is better not to leave them in acidic water for a long time (weeks).  Acidic water slowly dissolves their shell (usually in form of tiny holes).

The same goes for temperature. Assassin snails can easily thrive in a wide range of temperature conditions 18 – 30 C (64 – 86 F). However, the optimal temperature should be in the range of 24 – 28 C (75 – 82F). Especially, if you are planning to breed them.

When the temperature drops too low for Assassin snails their metabolism slows down and they tend to bury until it is warm enough.

Lighting

No special requirements. Lighting should be adapted to the needs of plants in the tank.

Read more about it in my article “Advanced Guide to Planted Tank Lighting”.

Substrate

Assassin snails will thrive in aquariums with sandy or soil substrate that they will be able to delve into. Ideally, your substrate should be deep enough to burrow down into the ground and disappear.

First of all, it will give the aquarist an opportunity to watch their natural behavior. Second, the soft substrate plays a major role in breeding. Hard substrate (rocks, gravel) prevents them from burring that can stress them a lot. In addition, newly hatched and baby Assassin snails tend to spend a lot of time hidden underground.

By sifting through the substrate, they also prevent the risk of gas pockets being built up which can be very dangerous to your fish or shrimp.

Important: Do not forget to acclimate your snails. When adding new Assassin snails to your tank, go slowly and gently. Read my article “How I drip acclimate shrimp and why” and use the same principle. 

Be careful with chemicals like copper (read more). Crabs, shrimp, and crayfish do not tolerate copper-based medications.

Basic Tank Equipment (links to check the price on Amazon) Filter: Marineland Penguin Power, Sponge filter, Matten Filter. Aquarium pump: Tetra whisper Air pump  Inert Substrate: Carib sea sand, Play sand, etc. Decor: Malaysian Driftwood, PVC pipes, Coconuts, Decorations, etc.

Mating Assassin Snails

Clea Helena is gonochoristic and fertilization is internal. This means that both a female and a male snail must be available for them to reproduce.

There is no apparent sexual dimorphism in the shell structure. Males and females cannot be distinguished by external features. That is why it is necessary to have at least 4 – 5 Assassin snails to ensure that both male and female are present.

In Clea Helena, courtship starts with the male climbing over a female shell and holding it firmly for a period of 20 – 30 minutes. After that, the male slightly slides towards the female right side and starts grasping with his penial sheath searching for genital aperture. During this process; the male transfers semen to the female.

According to the observations, copulation can last for 3 – 5 hours. It usually occurs in a night time. In some cases, the mating activity may be communally. Eventually, the males and females separate, and the females go off to lay their eggs on a hard surface such as driftwood, rocks, glass, or plant stems) presumably as a protective mechanism.

Breeding Assassin Snails

The fertility rate of Clea Helena is pretty low. Females usually deposit between 1 to 4 egg capsules per clutch in a straight line, separated from each other by 5 mm approximately.

Eggs capsules are square in shape, nearly transparent, and approximately 3 to 4 mm in width and length. The eggs in the capsules are less or about a millimeter in size.

Over a period of 46 – 58 days, the white-yellowish egg turns light brown, it means that the embryo undergoes complete non-feeding, benthic development before hatching.

Important to know: The higher the temperature the faster they will hatch. Assassin snails do not breed at all if the temperature drops below 20C (68F).

Newly hatched baby Assassin snails are about 3 – 3.5 mm in size and resemble the adults in shell shape and color although typical shell stripes are not clearly marked yet. They do not stay on the substrate and prefer to bury into the substrate feeding on microorganisms they find there. Therefore, it is absolutely important to have soft substrates in breeding tanks.

Juveniles will usually appear on the surface once they are 2 – 3 months old by that time they have a shell length of around 8 – 10 mm (~0.4 inches). They eat the same food just like the parents.

Unless there is an infestation of pest snails in the tank, and temperature suites them, do not expect Assassin snails to breed systematically.

In most cases, it will take several months before you can get first baby snails. The good this, though, is that baby snails have a very high survival rate.

Assassin Snail and Pest Snails Control

Assassin snails have become targeted by the freshwater ornamental trade industry, due to their predation abilities on other snail species that frequently became aquarium pests such as Bladder snails, Pond snails, Ramshorn Snails, and Malaysian Trumpet Snails.

Nonetheless, in some cases, people are not satisfied with the results. They complain that Assassin snails do not eat them fast enough. There can be several reasons for that:

1. Too much other food. As I have said earlier, their efficiency drastically decreases if there are other food sources. Therefore, if you see that your Assassin snails thrive and breed it is a sure sign.
   Solution: Feed them less. Make them work for it.
2. Consumption rate: Depending on the size of the prey, Assassin snails need to eat 1 – 3 snails per 1 – 3 days. Therefore, do not expect miracles. They cannot eat non-stop.
   Solution: Be patient and they will do their job eventually unless there are so many pest snails that they breed even faster.
3. Low temperature: Assassin snails are not very active if the temperature is too low for them. In addition, low temperature prevents them from breeding, which takes a lot of energy. Therefore, if they do not reproduce, their appetite is also
4. Prey size: Assassin snails cannot enter into the cavity of the small snails. Their proboscis is too big for that. Lots of aquarists noticed that Assassin snails will ignore snails if their prey is smaller than 1/10th of their size or so.
   Solution: You have to wait.

Assassin Snails and Suitable Tank mates

Snails

Assassin snails are active predators of snails. They will be a serious threat to any freshwater snail species in the tank. There is no safe snail for Assassin snails.

Every now and then I see different posts on forums and Facebook groups where people ask can they keep them with big snail species like Mystery snail, Chopstick Snail, Rabbit Snail, Japanese Trapdoor Snails, etc. Sometimes people say that they have been keeping Assassin snails even with Nerite snails without any problem.

Personally, I would not recommend doing it. If it works for them, it does not mean that it will work for you.

Sooner or later but your luck will run out especially if you have several of them. It is a pretty interesting fact that Assassin snails can behave like a pack hunter in attacking larger snails.

Therefore, do not keep other snails with them, they will try to eat any snail.

Note: Snails without an operculum are particularity vulnerable to attack. However, even snails with an operculum, like Trumpet Snails, are no match for a hungry Assassin Snail.

Dwarf Shrimp

There are also some conflicting data about Assassin snails compatibility with dwarf shrimp. Some people say that they will be fine with dwarf shrimp. Others witnessed some aggression or at least strange activity.

Some time ago I researched this topic and came to the conclusion that Assassin snails do eat shrimp. So, the answer is absolute 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. The point is that healthy shrimp are too fast for them to catch. Therefore, if they catch weak shrimp it leads you to have a stronger better shrimp colony later on.

Therefore, if they caught a shrimp, you can tell yourself that they did culling for you. Read more about “Culling Shrimp. Selective Breeding.”

Do Assassin snails attack dwarf shrimp very often? No, they do not. On the contrary, these incidents are pretty rare but they happen.

Fish

Do not keep them in aquaria that contain Cichlids, Loaches, Goldfish, Pufferfish, or any large/aggressive species that have a voracious appetite for invertebrates.

Their tankmates should include other calm and peaceful community tank fish (for example, Pygmy Cory Catfish, Otocinclus Catfish, etc.).

Crayfish and Crabs

Keep Assassin snails away from all types of freshwater crabs (except Thai Micro Crabs), crayfish (even Dwarf Mexican crayfish), and even some types of predatory shrimp such as Macrobrachium family.

All of them can be very aggressive towards the snails.

In Conclusion

Assassin snails are freshwater snails that do not require special care. Even without their beneficial task of consuming pest snails and meaty residues, they are very personable snails that are quite beautiful in appearance.

They are also considered to be quite hardy and can be a great addition to any freshwater tank. 

Related articles:

• List of Freshwater Aquarium Snails. Pros and Cons
• If you have more questions about snails, check out my article “30 Frequently Asked Questions about Snails in Freshwater Tanks.
• Benefits of Snails for a Shrimp Aquarium. 

References:

1. Effect of Diet and stocking densities on life history traits of Clea helena (Philippi 1847) reared in captivity. J Aquac Res Development 2013;4(5):1-4. http://dx.doi.org/10.4172/2155-9546.1000187.
2. Biological control of the invasive snail species Melanoides tuberculata and Tarebia granifera in Zaporizka Nuclear Power Plant cooling pond. Ukrainian Journal of Ecology, 2018, 8(1), 975-982 doi: 10.15421/2017_301.
3. Trematode infections of freshwater snails genus Clea a. adams, 1855 in the reservoir of lower Northeast Thailand. J I T M M Proceedings 6 (2017) 7-16.
4. Biological and biomechanical principles of the controlling molluscs Melanoides tuberculata (Müller 1774) and Tarebia granifera (Lamarck, 1822) in reservoirs of strategic importance. WSN 99 (2018) 71-83.
5. Survey of Aquatic Snail Genus Clea and a Potential as Predator of Aquatic Pest Snails. Department of Agriculture. 2017.
6. First non-native establishment of the carnivorous assassin snail, Anentome helena (von dem Busch in Philippi, 1847). BioInvasions Records (2016) Volume 5, Issue 3: 143–148. DOI: http://dx.doi.org/10.3391/bir.2016.5.3.04.
7. Assassin Snail (Anentome helena). Ecological Risk Screening Summary. U.S. Fish and Wildlife Service, 2018.
8. Strong et al. (2017), Quid est Clea helena? Evidence for a previously unrecognized radiation of assassin snails (Gastropoda: Buccinoidea: Nassariidae). PeerJ 5:e3638; DOI 10.7717/peerj.3638