If your tank has been overrun by pest snails, the assassin snail is the natural solution most experienced keepers reach for. This small, striking snail, with its yellow and brown banded shell, hunts and eats other snails. It is slow and steady rather than instant, but it is chemical-free, safe for fish and plants, and interesting to watch in its own right. This guide covers how assassin snails work, how to keep them, and what to feed them once the pests are gone.
Assassin Snail at a Glance
| Scientific name | Anentome helena (also listed as Clea helena) |
| Adult size | 2 to 3 cm |
| Lifespan | 2 to 3 years |
| Minimum tank | 20 litres |
| Temperature | 22 to 28°C |
| pH | 7.0 to 8.0 |
| Hardness | Moderate to hard |
| Temperament | Peaceful with fish, predatory with snails |
| Diet | Carnivore |
Where Assassin Snails Come From
Assassin snails are native to Southeast Asia, including Thailand, Malaysia and Indonesia, where they live in rivers and lakes with sandy or muddy bottoms. In the wild they eat other snails, worms and carrion. In the aquarium they are prized for exactly that appetite.
How Assassin Snails Control Pest Snails
Assassin snails hunt using a long proboscis, which they push into another snail’s shell to feed. They are most effective against the common pest species: bladder snails, pond snails, ramshorn snails and Malaysian trumpet snails.
A few things to expect:
- It takes time. An assassin snail may eat one snail every few days. A heavy outbreak can take several weeks to months to bring under control.
- Numbers matter. As a rough guide, one assassin per 20 to 40 litres suits a moderate pest problem. Add a few more for a severe outbreak.
- They will not wipe out every snail. Populations usually drop to a low, stable level rather than disappearing entirely.
- Help them along. Reduce overfeeding, which is what fuels most pest snail booms, and remove snails by hand alongside the assassins. Our guide to getting rid of pond snails without chemicals covers the full approach.
Are Assassin Snails Safe With Other Snails?
Not entirely. Assassins target the snails they can reach, and that can include ornamental species:
- Nerite snails: usually safe once fully grown, as their tough operculum seals the shell. Small nerites can be at risk.
- Mystery snails: large adults are usually left alone, but smaller or weakened mystery snails can be eaten.
- Rabbit snails: large adults are generally safe; juveniles are at risk.
- Baby snails of any kind: likely to be eaten.
If you keep ornamental snails you value, especially young ones, think carefully before adding assassins. Our guides to nerite snails and mystery snails cover those species in more detail.
Are Assassin Snails Safe With Shrimp and Fish?
Yes, for the most part. Assassin snails are too slow to catch healthy fish or adult shrimp. They may scavenge on a shrimp or fish that has already died, which is useful clean-up behaviour. Very occasionally, a newly moulted or weak shrimplet may be taken, but most shrimp keepers find them compatible.
Tank Setup
- Tank size: they suit any tank of 20 litres or more.
- Substrate: sand or fine gravel is ideal. Assassin snails love to bury themselves, often with just the siphon sticking out, and ambush prey from below.
- Plants: completely plant safe. They do not eat plants.
- Lid: they rarely climb out, but a lid is always sensible.
- No copper. Copper is toxic to all snails. Check fish medications and fertilisers before using them.
Water Parameters
- Temperature: 22 to 28°C.
- pH: 7.0 to 8.0.
- Hardness: moderate to hard. Snails need calcium to build healthy shells. In very soft or acidic water, shells can thin, pit and crack. If your water is soft, a calcium source such as a mineral supplement or a piece of cuttlebone helps.
- Ammonia and nitrite: always zero.
What to Feed Assassin Snails
Snails are their preferred food, but assassin snails do not starve once the pests run out. They readily take other protein foods:
- Sinking carnivore pellets and wafers
- Frozen bloodworm and brine shrimp
- Leftover fish food that reaches the bottom
In a community tank, they usually find enough leftovers on their own. If your tank is very clean, drop in a little frozen bloodworm, such as Betta Choice Frozen Bloodworm, every few days. For a wider look at snail diets, see our guide to feeding aquarium snails.
Breeding Assassin Snails
Unlike pest snails, assassin snails breed slowly, so they will not overrun your tank. They have separate sexes, so you need at least one male and one female, which is easiest to achieve by keeping a small group.
- Females lay single eggs in small, clear, square capsules on hard surfaces such as rocks, wood and glass.
- Each capsule holds one egg, and a female lays only a few at a time.
- Eggs hatch in about three to four weeks, depending on temperature.
- The babies bury into the substrate and are rarely seen for several months until they reach about 1 cm.
This slow breeding is a big part of their appeal: they control pests without becoming a pest themselves.
Signs of a Healthy Assassin Snail
- Moves around and buries regularly
- Smooth, intact shell with clear banding
- Firm grip on surfaces and responds to touch
A snail that lies upside down for long periods, has a receding body or gives off a strong smell may have died. Remove dead snails promptly to protect water quality.
Buying and Acclimatising Assassin Snails
Snails are sensitive to sudden changes in water chemistry. Acclimatise them slowly, ideally by drip, over 30 to 60 minutes. Place them on the substrate rather than dropping them through the water. You can find our assassin snails in the snail category, delivered by tracked courier in insulated packaging.
Frequently Asked Questions
How many assassin snails do I need?
About one per 20 to 40 litres for a moderate pest problem. Add more for a severe outbreak.
How long do assassin snails take to clear pest snails?
Usually several weeks to a few months, depending on the size of the outbreak and how many assassins you add.
Will assassin snails eat nerite snails?
Fully grown nerites are usually safe. Small or juvenile nerites can be eaten.
Will assassin snails overpopulate my tank?
No. They lay single eggs slowly, and numbers stay manageable.
What do assassin snails eat when there are no snails left?
Sinking protein foods, frozen bloodworm and leftovers. They adapt well.
Assassin snails are one of the simplest, safest ways to keep pest snails in check. To learn more about the wider world of aquarium snails, read our article busting common myths about freshwater snails.