Quick Stats
Minimum Tank Size: 29 Gallons (110 Liters)
Care Level: Moderately Difficult
Water Conditions: PH 6.5-7.5 and Moderately Hard to Very Hard
Temperature: 65-77 °F (18-25 °C)
Maximum Size: 3 inches (7.5 cm)
The assassin snail (Clea helena) is freshwater snail that is highly sought after in the aquarium trade for their ability to prey on pest snails. They are found throughout much of Southeast Asia, and are native to Thailand, Malaysia, and Indonesia.
They primarily inhabit small bodies of water, and are most commonly found in ponds or ditches. They prefer locations with a sandy or muddy substrates, and these conditions should be reproduced as closely as possible in the home aquarium.
Assassin snails do particularly well in captivity, and most will grow up to 3 inches (7.5 cm) in length. The average life span is around two years, though they can easily exceed this age in a well maintained aquarium.
Housing
Assassin snails really only thrive in mature aquariums, and the minimum tank size for this snail is 29 gallons (110 liters). At first glance, this may seem to be an overly large tank size for such a small snail, but it should be noted that they do not breathe air like most other aquarium snails. Because of this, they are very sensitive to the water quality.
They must be provided with a soft substrate that allows them to burrow. Sand is generally the best choice, but there are numerous other substrates on the market that will also work. Adult assassin snails spend much of their time in the substrate, and they often ambush other snails from their position of concealment there.
Assassin snails have no interest in aquatic plants, and are safe in any planted aquarium. In fact, many people keep these snails in aquascaped tanks to deal with any unwanted pest snails that may be accidentally introduced.
A word of caution though – there have been numerous reports of assassin snails eating fish eggs, and even immobile wrigglers. So they should not be kept in breeding tanks, unless you are breeding live bearers.
Feeding
An assassin snail’s natural diet is mainly composed of other species of snails and worms, though they are also opportunistic feeders. They will eat almost anything that they can scavenge, and this includes decomposing fish and other small invertebrates.
Because of their varied diet, they are very easy to feed in the home aquarium. If there is a significant snail population in their tank, then there is often no need to feed them at all.
However, if there are no snails for them to eat, then they should be fed with a high protein food. Some aquarists feed them frozen blood worms, or brine shrimp, but any sinking food will do. The best choices are either Wardley Shrimp Pellets 
Breeding
Assassin snails have defined males and females, and are not hermaphroditic like many other snails. It is nearly impossible to sex these snails, so if you are planning to breed them, a minimum of six individuals should be introduced to ensure an adequate mix of the sexes.
When they begin to copulate, they will lock together for approximately 12 hours. After they are done, the female will then deposit several single eggs. The eggs are often deposited on plants or driftwood, though you may also see them on ornaments, or even the aquarium glass. They are roughly square in shape, with a brown sack at the center.
The eggs generally hatch after a few weeks (usually between 3-8 weeks), though the amount of minerals in the water can influence the incubation time. Once hatched, the juveniles will burrow into the substrate, and are rarely seen again until they reach maturity. Maturity is usually reached after about six months, and at this time, they will emerge from the substrate more regularly.
They breed very slowly for a snail, and so rarely become a pest on their own. However, they can be difficult to completely remove from an aquarium, since they spend so much of their time buried in the substrate.
Compatibility
Assassin snails themselves are preyed upon by larger cichlids, or any of the more common snail eating fish. While they are protected by an operculum, they will often become injured and stressed from the constant attacks of a fish. If the attacks continue, they will either die, or have a greatly shortened life span.
Almost any other snail that is kept with an assassin snail is at risk. While extremely large snails like apple snails are generally safe, it is not unknown for assassin snails to “gang up” on larger snails, and devour them. Only place these snails in an aquarium if you are prepared to lose any snails that share a tank with them.
Snail Control
Assassin snails are renowned for their ability to deal with problem snails in an aquarium, and just a handful of these snails can deal with even a massive Malaysian trumpet snail infestation. Because of this, they are rapidly growing in popularity, and more and more fish stores are starting to carry this snail.
i got about 50 tiny eggs stuck up one corner of my tank, already last year moved 21 to my big tank. Problem is when cleaning tank substrate tine ones are easily sucked up and disposed of, i sift all debris before disposing
This is my problem! I have five snails including one baby. I have tons of eggs everywhere. I do not know how to clean cause I don’t want to disturb these eggs. I have about 25 eggs all total. It’s a 2 gallon small filtered and heated aquarium. I used to have a beta in there and he passed. So now my assassins are breeding like CRazy!! I have to clean this tank it’s getting dirty and smelly. What to doooo??
It should be relatively easy to clean if you have a siphon. Just carefully siphon out the water and avoid placing the tip of the siphon anywhere near the eggs. But I wouldn’t be too concerned, as the eggs are pretty strongly attached and shouldn’t be disturbed too easily.
Leave the glass alone and get some cherry shrimp. The shrimp will feed off the biofilm, algae, and most waste left at the bottom. Put a prefilter on the end of your gravel vac and only vacuum the top of the gravel. Run a good in-tank sponge filter and keep the tank out of sunlight. Throw in a couple live plants (potted in aquasoil) to help suck up the free nitrates. Shrimp, live plants, and sponge filter will make your tanks a lot more maintenance free and stable. I pick up debris, do about a 10% water change each week and wring out the sponge filter in the waste water, then top off with RODI water and mineral supplement. Takes about 10 mins tops to do.
Foam filters, and a current generator. Connect an air pump to both of them, and have each on opposite sides of the tank. They will break down the debris faster, and it will be sucked into your filters. Now you just have to clean the filters every week. This the setup I have for my goldfish. It does all the work for me.
How big is your tank? I gave a patio pond for 3 goldies and I want to keep them, have them for next summer too. But the only empty tank I have is a 10 gallon. Would your setup be enough for them if I clean filters very often?
Why do you suggest that these snails not be feed algae discs containing spirulina? The ones mentioned in this article by Wardley are made from spirulina so I am confused.
Oops, I made a mistake. The food you suggested does NOT have spirulina.
2 of my assassin snails are upside down on the substrate with their bodies pulled into their shells – have they died? They were acclimated to the tank before being put in and were moving around but a few days later now on the substrate like this…
i transferred 28 from a 4 foot tank to my 6 footer, I rarely see them, apart from on back withdrawn into shell, just observe it for a few days and it will have gone on a walk about. They I think are to the rear of the tank were there is deeper substrate/rock and plants. I may get the odd one out and about, I actually think it is out for a nosy. when cleaning the smaller tanks substrate I use a very fine kitchen sieve/slowly bit by bit. I then put the smaller ones into the bigger tank, noting the number, the large ones appear frequently on top of the (2) internal filters
I would flip them over, as sometimes fish will upend them and sometimes they have a hard time flipping back over. But if they’re on they’re backs, it’s not the greatest sign. You can always do the smell test: remove them from the aquarium and smell them. If they smell rotten, then they’re dead. It’s the only way to know for sure with snails sometimes.
difficult to breed? i’m from southeast asia and these snails reproduce like crazy, bought them to remove pest snails but they actually reproduce to the point that even 5 of my snail sucking clown loaches can’t even eat enough and they’re now the pests, i’m regreting my desicion to buy these snails…
What i keep hearing too. Hard to breed, slow to breed… I got 12 assassin snails 3 years ago. I now have thousands.. i recently got puffers. Might as well use my large supply of assassin snails as food lol. im in southern Florida. my mother in law got 12 assassin snails i mailed her in Arkansas. Hers have not bred in almost 2 years. She still has 12. . So i dont know if its the weather or what. Its either spring like or summer here year round. People keep saying their slow breeders. Hard to breed..About every 2 to 3 weeks, i see a new batch of tiny ones crawling up the tank walls. I got pest snails and put assassin snails in to deal with them in 2 of my tanks. 6 in each. Both tanks are now infested with assassin snails. So both tanks went from 6 assassin snails to thousands in both tanks in 3 years. Wish i was exaggerating. Ive been giving our local owned aquarium store assassin snails for a year. Yesterday when i had a bag full to give her, she said to date ive given here over 2 thousand of the suckers. She sells 12 for 10.99. So she making some cash off my assassin snail infestation lol she gave me some puffer fish and a tank set up for them to help me cut down on snails. Old 55 gallon. I put as many as i could get in new tank she gave me.. I am not making a dent in the population giving them away by the hundreds. i have a 125 gallon and 200 gal and 40 gal. 2 tanks are loaded with them. I recently set up a 10 gallon to just put assassin snails in from my canister filters.. its ridiculous how much they are breeding. Its as bad or worse then pest snails. My pest snail problem was never this bad… least assassin snails are cleaner. they dont leave the mess pest snails do. Im thinking the warm weather is the culprit? Or we just got a breed of horny assassin snails lol i counted 13 pairs attached to each other this morning. so here comes more batches Of assassin snails! Hard to breed and slow to breed my butt! Lol and no.. i dont over feed my fish and vacuum exess out daily. ive been trying to cut down on the snails food they get. I dont know why they are breeding like crazy.
It sounds like you could start a snail selling empire. lol. If you figure it out the trick, you should share it with the rest of us.
I will happily take some off your hands. I have a few in my tank for a few years but haven’t had any luck with babies. Maybe I vacuumed them up when I clean the gravel?? I’ve seen them mating, and I have seen some eggs, just no mini snails….
i have seen eggs on the glass now i have fish in the tank as well as 2 plec s would these fish eat the eggs as i have not seen the eggs on the glass now and only been 3 days.
In my experience, common plecos will definitely take the opportunity to eat eggs or hatchlings. But if you have bristlenose plecos, it’s much less likely that the eggs will be eaten.
i did see two lots on the glass i only have 2 young plecs that are about 1-1/2 inches long at the moment white blue eyed ones and one sucking loch . .
thanks for your reply
Hello
How soon after the breeding are the eggs laid?
Thank you
i have hundreds of assassin snail here and are selling them at 25 pence each . collection only .
I have no idea HOW they got in my tank! Could they have come in frozen brine shrimp?
Do you have live plants? Most often the hitchhike in on live plants.
I have hundreds of small assassin snail babies and am overhauling my tank and starting from scratch. I am interested in transferring these to a little 10 gallon tank with the substrate and a few remaining plants and basically tucking the tank into the garage and forgetting about it. Will the snails grow in these conditions or am I crazy? They seem pretty low maintenance. Weather permitting, of course. And I’ll do water changes as needed. I’ll drop some food in now and then. Thanks for any advice!
The main problem would be lack of food. You’ll need to make sure to provide them with regular snails or food for them. I know I’ve had success with bloodworms but some people have also used fish flakes to keep them fed.
I have an issue I have a single assassin snail, in a 20 gallon tank. They were originally 2 but one died soon after I bought it. I was very happy cause my pest snail issue was fully resolved but just recently I realized my snail has reproduced several babies. Not sure how it’s possible as I’m reading everywhere they are not asexual but I also don’t know what to do and I don’t necessary want a full tank of assassin snail. any suggestions?
This is one of the greatest problems with assassin snails, and one I’ve encountered myself. Unfortunately, once they’re established in a tank they’re very hard to get rid of. The only option is to try and remove them by hand – a difficult prospect since they burrow. I wish I could offer more help.