The Complete Truth About Assassin Snails and Shrimp
Let’s cut through the forum noise. You’ve read conflicting opinions everywhere. Some say “they never eat shrimp.” Others claim “they killed all my cherries.” Who’s right?
Both. And neither.
Here’s what actually happens based on 9 years of breeding experience and research:
When Do Assassin Snails Actually Eat Shrimp?
They catch shrimp in exactly four situations:
- The shrimp is molting. Soft, immobile, can’t escape. Easy target.
- The shrimp is sick or dying. Slow movement, no energy to flee.
- The shrimp is genetically weak or “stupid.” Doesn’t react to danger properly.
- You’re confusing them with the molt. Most “assassin ate my shrimp” stories are actually someone finding an empty exoskeleton with an assassin crawling nearby. The snail is scavenging the shed shell for calcium — it didn’t kill anything. Check carefully before you panic.
From an ecological standpoint, this is actually natural culling. The assassins remove weak individuals, leaving you with a stronger colony. Read more about culling here.
What Professional Shrimp Breeders Say
I’ve spent countless hours digging through forums, German breeding sites, and Russian shrimp groups. The two quotes below are from 2017 — back when I was just starting this site.
Looking back, nothing has changed. Assassin snail biology hasn’t been updated, their behavior is the same, and every new breeder I’ve talked to since then confirms the exact same pattern. Here’s what they said back then:
- 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.” He also mentioned there is always a chance an assassin goes into “Rogue mode” and starts chasing shrimp.
- Flip Aquatics: “I really do believe assassin snails will eat shrimp. I think it is extremely rare and I think it is like a great white eating a person… so if they get a taste for shrimp and they like the shrimp, they are going to continue to chase after them.”
A Scientific Look at “Rogue Mode”
With all due respect to these breeders — they’re well-known in the community and I’ve learned a lot from their content — their ideas about “Rogue mode” and “getting a taste for shrimp” don’t fully match what we know about snail biology.
After studying snail external anatomy and internal anatomy in depth, here’s what actually happens:
- Assassin snails don’t have a reward system. Unlike mammals, they don’t get a dopamine hit from killing prey. Their nervous system is primitive — just a few ganglia, not a complex brain. They can’t “develop a taste” for something the way a great white shark can. No reward pathways. They respond to chemical signals (food scent), not learned behavior.
- They’re opportunistic scavengers, not hunters. If an assassin catches a shrimp, it’s because the shrimp was slow (molting, sick, or injured). A healthy shrimp is faster than any assassin snail — period.
- What looks like “Rogue mode” is usually starvation. If you stop feeding your assassins and they’re out of pest snails, they’ll scavenge anything slow. That’s not a behavioral switch — that’s hunger.
I’ve kept assassins in shrimp tanks for years. I’ve never seen one “switch” to exclusively hunting healthy shrimp after eating one. The breeders who report this are probably heavily underfeeding their snails or keeping them in tanks with weak/dying shrimp.
Bottom line: If you keep your assassins well-fed, they have zero interest in chasing healthy shrimp. The “Rogue mode” idea makes for good YouTube content, but it doesn’t match the biology.
Neocaridina vs Caridina: Risk Assessment
| Shrimp Type | Risk Level | Recommendation |
|---|---|---|
| Neocaridina (Cherry, Blue, Yellow) | Low | Safe for most tanks. Occasional losses are natural culling. |
| Caridina (Crystal Red, Taiwan Bee) | Medium-High | Not recommended. High-value shrimp make losses unacceptable. |
| Amano Shrimp | Very Low | Too large and fast. Completely safe. |
How to Prevent Assassin Snails from Eating Shrimp
The ONLY time assassins actively hunt shrimp is when they’re starving. Follow these rules:
- Feed them regularly. If you don’t have pest snails, drop a sinking carnivore pellet or frozen bloodworm once a week.
- Don’t overstock. One assassin per 10 gallons (40 liters) is enough for maintenance.
- Remove dead shrimp immediately. If an assassin gets a taste for dead shrimp, it might start hunting live ones.
The Molting Trap — How to Protect Your Shrimp
Molting is the only time healthy shrimp are genuinely vulnerable. Here’s how to minimize losses:
- Provide dense cover. Java moss, shrimp tubes, and leaf litter give molting shrimp places to hide where assassins can’t reach them.
- Keep GH above 6. Proper mineralization means faster, cleaner molts. Slow molts = longer vulnerability window.
- Don’t overfeed your assassins. A full assassin ignores a molting shrimp. A starving one doesn’t.
- Leave the molt in the tank. Shrimp eat their own exoskeleton to recover minerals. If you remove it, they’re weaker next time — and more vulnerable to assassins.
The Bottom Line
If you keep cheap Neocaridina, the risk is minimal. If you keep expensive Caridina, the stress and occasional loss of a valuable specimen aren’t worth the risk. Keep them in separate tanks.
For complete assassin snail care — feeding, breeding, tank setup, and water parameters — read our detailed assassin snail guide.
Frequently Asked Questions
Will assassin snails eat my cherry shrimp?
Only if the shrimp is molting, sick, or too slow to escape. Healthy cherry shrimp are completely safe. Expect occasional losses as natural culling.
Can assassin snails live with Caridina shrimp?
Technically yes, but it’s not recommended. Caridina are high-value shrimp, and even rare losses are unacceptable. Keep them in separate tanks.
Do assassin snails eat shrimp eggs?
No. They cannot reach shrimp eggs carried under the shrimp’s tail. They also don’t hunt berried shrimp.
Do assassin snails eat baby shrimp (shrimplets)?
Very rarely. Shrimplets are tiny and hide constantly. Assassins prefer larger, easier prey. The risk is minimal.
How many assassin snails can I keep with shrimp?
One assassin per 10 gallons is enough for maintenance. More assassins = higher risk of starvation = higher chance they’ll hunt shrimp.
Will assassin snails eat Amano shrimp?
No. Amano shrimp are too large and fast. Completely safe.
My assassin snail is hunting shrimp! What do I do?
Feed it immediately. Drop a sinking carnivore pellet or frozen bloodworm. A well-fed assassin has zero interest in hunting live shrimp.
Great post, thank you
Thanks!
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 🙂
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.
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,
Michael
Will shrimps eat on the assassins snail eggs? Can you breed them both in the same tank?
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,
Michael
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….
Hi Aritcia,
WOW!
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,
Michael
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?
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,
Michael
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.
Hi VISHWAS SINGH,
It is true. Sometimes it may happen.
Thank you for the feedback.
Best regards,
Michael
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.
Hi Victor,
Awesome!
Thank you for sharing your experience.
Best regards,
Michael
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?
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,
Michael