Quick answer: Assassin snails (Anentome helena, often sold as Clea helena) are small, striped freshwater snails that hunt and eat other snails. They grow to about 0.75 to 1 inch (2 to 2.5 cm), live 2 to 3 years, and do best at 72 to 82 F with pH 7 to 8 and hard water. They’re a natural way to control pest snails like ramshorn, bladder and Malaysian trumpet snails, and they breed slowly, so they won’t take over your tank. They’re safe with fish and usually with adult shrimp. What most people get wrong is expecting fast results. A few assassin snails take weeks to months to clear a big infestation, and they won’t fix the real cause, which is too much food.
Assassin snail at a glance
| Detail | Assassin snail |
|---|---|
| Scientific name | Anentome helena (formerly Clea helena) |
| Other names | Bumblebee snail, snail-eating snail |
| Origin | Rivers and lakes in Southeast Asia |
| Adult size | About 0.75 to 1 in (2 to 2.5 cm), often smaller |
| Lifespan | About 2 to 3 years |
| Temperature | 72 to 82 F (22 to 28 C) |
| pH | 7.0 to 8.0 |
| Hardness | Moderate to hard, GH 8 dGH or higher |
| Minimum tank | 5 to 10 gal (19 to 38 L) |
| Diet | Carnivore. Snails, snail eggs, dead fish, sinking protein foods |
| Temperament | Peaceful with fish. Predator of other snails |
| Breeding | Separate sexes. Lays single eggs, breeds slowly |
| Care level | Easy |
What snails do assassin snails eat?
| Snail | Will assassins eat it? | Notes |
|---|---|---|
| Ramshorn snails | Yes, readily | One of their favorite foods |
| Bladder and pond snails | Yes, readily | Thin shells, easy prey |
| Malaysian trumpet snails | Yes, but slower | Trumpets hide in the substrate, so it takes longer |
| Snail eggs | Yes | They eat many egg clutches too |
| Mystery snails | Adults usually safe, small ones at risk | Large adults can close their trapdoor. Small or weak ones may be attacked |
| Nerite snails | Sometimes | Adults are tough but not immune, especially small or weak ones |
| Other assassin snails | No | They live together peacefully |
How they hunt. Assassin snails use a long tube-like snout called a proboscis to reach inside another snail’s shell. Some also bury in the substrate and wait for prey to pass by. They also eat dead snails and dead fish, so they help clean up.
Assassin snail vs other ways to control pest snails
| Method | Speed | Shrimp safe? | Fixes the cause? |
|---|---|---|---|
| Assassin snails | Slow, weeks to months | Usually yes with adult shrimp | No |
| Feeding less | Slow but steady | Yes | Yes |
| Vegetable bait traps | Fast for removing many snails | Yes | No |
| Snail-eating loaches and puffers | Fast | No | No |
| Chemical snail killers | Fast | No, usually kill shrimp too | No, and dead snails can spike ammonia |
Here’s the honest part most assassin snail guides leave out. Assassin snails are a cleanup tool, not a cure. If a tank is full of pest snails, it’s because there’s extra food, from overfeeding, leftovers or melting plants. Add assassins without changing feeding and they’ll eat for months while the pest snails keep breeding. The best results come from doing both: cut feeding, trap the bulk of the pest snails, then let assassins mop up what’s left.
Appearance
Assassin snails have a tall, cone-shaped shell with bold yellow and dark brown or black spiral stripes, like a bumblebee. The body is gray to greenish. They have a trapdoor (operculum) and a long breathing siphon. Males and females look the same.
How many assassin snails do you need?
A rough guide that works for most tanks:
- Light pest snail problem: 1 to 2 assassin snails per 10 gallons
- Moderate problem: about 1 assassin per 5 gallons
- Heavy problem: cut feeding and trap first, then add assassins
Each assassin snail eats roughly one snail every day or few days, depending on its size and the prey. Expect visible results in a few weeks and most pest snails gone in 1 to 3 months.
Assassin snail tank setup
Tank size. 5 gallons is enough for 1 or 2. Larger tanks are fine, since they’ll roam and hunt.
Substrate. Sand or fine gravel lets them bury, which they do a lot. Don’t worry if you don’t see them for a day or two.
Water hardness. Like all snails, they need calcium for their shells. Keep pH at 7 or above and GH 8 or higher, and add crushed coral or cuttlebone in soft water.
Cycled tank. Add them to an established tank. Our how to cycle a fish tank guide shows how.
No copper. Copper in medications kills snails.
Lid. They rarely climb out, but a lid is still a good idea.
Here’s a video from our AQUA PLANET 128 channel about assassin snail care.
What to feed assassin snails
With pest snails in the tank, they feed themselves.
Once the pest snails are gone, feed them so they don’t starve or turn on your other snails:
- Frozen bloodworms or brine shrimp
- Sinking shrimp pellets and protein-rich wafers
- Leftover fish food that reaches the bottom
Feed a small amount 2 or 3 times a week.
Are assassin snails safe with shrimp and fish?
Fish: yes. They can’t catch healthy fish. They will eat dead fish, which helps keep the tank clean.
Adult shrimp: usually yes. Healthy Amano shrimp, cherry shrimp and other adults are generally left alone.
Baby or weak shrimp: a small risk. Some keepers report assassins catching shrimplets, especially when other food runs out. In a valuable shrimp breeding tank, use traps and lighter feeding instead.
| Good tank mates | Avoid |
|---|---|
| Small peaceful fish like tetras, rasboras and danios | Clown, yoyo and other snail-eating loaches |
| Corydoras and plecos | Pea puffers and other puffers |
| Adult shrimp | Shrimp breeding tanks with valuable shrimp |
| Large adult mystery snails | Small nerite and mystery snails you want to keep |
Assassin snail eggs and breeding
Assassin snails have separate sexes, and since males and females look alike, a group of 4 to 6 usually includes both.
Eggs. Females lay single eggs, each in a small, clear, square-ish capsule about 1 to 2 mm across with a yellow center, stuck to rocks, wood, glass or plants.
Hatching. Eggs take roughly 3 to 8 weeks to hatch, depending on temperature.
Babies. The tiny snails bury in the substrate and stay hidden for several months while they grow, feeding on detritus and leftovers. You often won’t see them until they’re about a quarter inch long.
Why they won’t overrun your tank. They lay only a few eggs at a time and grow slowly, so populations stay small. Some keepers even sell or trade their extras.
For help telling their eggs apart from other snail eggs, see our aquarium snail eggs guide.
Common assassin snail problems
They’re not eating the pest snails. There’s plenty of other food. Cut back feeding so the assassins get hungry and hunt.
Can’t find them. They’re probably buried. That’s normal.
Assassin snail not moving. They often rest or bury for a day or two. Check for a bad smell or a loose trapdoor to rule out death.
Eating snails you wanted to keep. Move small nerites or mystery snails to another tank, or keep the assassins well fed.
Cracked or thin shells. Low calcium or low pH. Add crushed coral or cuttlebone.
Pest snails keep coming back. The tank still has too much food. Feed less and remove melting plants. Our plants melting guide helps with that.
A note before you buy
Assassin snails can harm native snails if released, and they’re restricted in some countries and regions. Check your local rules, and never release aquarium snails into ponds, lakes or rivers.
FAQ
Do assassin snails eat other snails?
Yes. They eat ramshorn, bladder, pond and Malaysian trumpet snails, plus snail eggs. Large adult mystery snails are usually safe.
Will assassin snails eat nerite snails?
Sometimes. Healthy adult nerites are usually tough enough, but small or weak ones can be attacked.
Are assassin snails safe with shrimp?
Usually with adult shrimp. They may occasionally eat baby or weak shrimp, so skip them in valuable shrimp breeding tanks.
How many assassin snails do I need?
About 1 to 2 per 10 gallons for a light problem, or 1 per 5 gallons for a bigger one. Cut feeding at the same time.
How fast do assassin snails work?
Expect results in a few weeks and most pest snails gone in 1 to 3 months.
Do assassin snails overpopulate?
No. They lay single eggs and the babies grow slowly, so numbers stay low.
What do assassin snails eat when there are no snails?
Frozen bloodworms, brine shrimp, sinking pellets and leftover fish food.
How long do assassin snails live?
About 2 to 3 years with good water and food.
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