FAQs on Snails in Freshwater Aquarium Assassin
Related Articles: Snails and
Freshwater Aquariums by Bob Fenner, In vertebrates for
Freshwater Aquariums by Neale Monks, Assassin Snails and
Sulawesi Elephant Snails. Keeping Clea and Tylomelania in the
Aquarium by Neale Monks, Fresh and
Brackish Water Nerites by Neale Monks,
Related FAQs: Freshwater
Snails 1, Freshwater Snails 2,
& FAQs on: Freshwater Snail
Identification, Freshwater Snail
Behavior, Freshwater Snail
Compatibility, Freshwater Snail
Selection, Freshwater Snail
Systems, Freshwater Snail
Feeding, Freshwater Snail
Disease, Freshwater Snail
Reproduction, Snails by Species: Apple/Baseball Snails,
Is a single Pomacea diffusa safe with single Clea helena - 2/11/2019
I have searched forums, the net, and your site, and have not been able to find
an answer to my question.
In my planted 10 gallon there is a Betta, a Pomacea diffusa and a Physa. This
evening I put in a single Clea helena (from a different tank) to deal with the
MTS, ramshorn and Physa offspring.
Am I looking for trouble as far as the Apple snail is concerned?
<Yes. In fact, just for you, I found this lovely video of an assassin snail
attacking and eating an apple snail, that I found on good old YouTube:
I can move the Assassin to a different, established tank if you think that would
be best and use another method to control the pest snail population.
<Or maybe you could temporarily move the apple snail?>
Photo from a month ago shows the size of Apple snail-about the size of a ping
pong ball, with the Physa on board.
<Clea helena are known to attack, kill, and eat snails larger than themselves.
Thus, in this case, the size of the apple snail alone is unlikely to make much
of a difference in terms of its likelihood of falling prey to the assassin
Thank you for your time.
Is a single Pomacea diffusa safe with single Clea helena
I have searched forums, the net, and your site, and have not been able
to find an answer to my question.
In my planted 10 gallon there is a Betta, a Pomacea diffusa and a Physa.
This evening I put in a single Clea helena (from a different tank) to
deal with the MTS, ramshorn and Physa offspring.
Am I looking for trouble as far as the Apple snail is concerned?
<Should be okay, especially if other prey/leftover food is available.>
I can move the Assassin to a different, established tank if you think
that would be best and use another method to control the pest snail
<Clea helena tends to consume small snails that it can overwhelm, rather
than biting chunks out of large prey. I've certainly kept them with
Tylomelania spp., and while juvenile Tylomelania were certainly eaten,
the adults did fine.>
Photo from a month ago shows the size of Apple snail-about the size of a
ping pong ball, with the Physa on board.
Thank you for your time.
<I'd say it's worth a shot, but I've not tried this combination myself,
so can't guarantee it. Cheers, Neale.>
Re: Is a single Pomacea diffusa safe with single Clea helena
Thank you Neale. I'll keep a close eye on the tank as I don't want the
Apple snail to feel threatened in his own home.
During my search elsewhere for answers, I could only find people talking
about an issue with multiple Assassins being a problem with one Apple
snail, and not the situation I've created.
<Indeed; but do be aware, as Sara suggested in her message.>
Very much appreciate your input.
snail issue; control. And plt ID
Hi Neale, hope you are well. My tanks are doing well, so I haven't
needed advice lately.
Here is a photo of a plant I'd asked about before. Someone told me
it's probably called naja grass. What do you think, have
you ever seen it?
<Certainly looks like Najas guadalupensis. But no, I've not
seen or kept it. Seems to be rarely traded here.>
It has long stringy roots but doesn't succeed in being planted for me at
least in the lower light setting.
<Correct. It looks much like other aquarium "tangle weeds" such as
Ceratophyllum demersum and Elodea spp. Basically, it wants to be left
loose, floating under bright light, and it will send down white roots to
form loose anchors onto the sediment. It'll grow from the waterline
downwards rather than from the substrate upwards.>
It tends to have explosive growth like the java ferns if it is growing
tangled among other floating plants.
The one I'm referring to in this picture is in the center and not the
annubias or the water wisteria/water sprite(i have both or one of
It's lacy and the roots are floating too.
Here is my real question though:
In your experience, do assasin snails ever get each other ever?
<Possibly, but this seems rare.>
I originally had 5. Some time back I found one smaller empty
Lately I had only ever been aware of 3, though it's possible one is
But today I noticed another empty shell, this was one of the larger
ones.... It's been there unmoved upside down since yesterday. I had
hoped these critters would eventually breed and not cannibalize. I
have heard stories that they do reproduce, but I have seen no evidence
<Ah, they do breed. But they're also unusual in not being
So if you (unluckily) got few/no females, then your population would die
Would they ever react badly to a water change, are they sensitive or
<They seem fairly hardy.>
It's heavily planted. This time I cleaned it a little more
thoroughly in the vacuuming, I changed a little more water than
typically (45% maybe as opposed to 25-30%, and my tank has a larger than
needed filter for currents), but there's also lots of decor and plants
and a well established filter, and the snails were removed and kept in
their water during the cleaning. The fish have shown no signs of
stress. They even gave birth since the cleaning. The endless
lime green endlers....
Do the assasin snails eat baby cherry shrimp?
<Some reports suggest they can, but it probably depends on many factors
including whether the baby shrimp had places the snails couldn't go,
like behind/inside filters, and how many of each you started off with.>
That tank could use some resident snail cleanup, but I would hate to
stick one in there and have him feasting on shrimp instead. I'm
wondering if there's anything that could coexist with them and do snail
patrol that wouldn't eat them too.... Probably not.
<I wouldn't keep Assassin Snails with my *only* group of Cherry Shrimps,
but I have combined them in one aquarium while keeping another
population of Cherry Shrimps going without Assassin Snails in another
The funny thing...I have never seen one eating a snail, even with baby
snails in the near vacinity. One in particular has been very
active since the clean. I wonder if he was the culptet in the
<Oh, Assassin Snails can/do eat snails, but they're scavengers more than
anything else, so if there is other food, they'll eat that as
<Most welcome, Neale.>
|Re: snail issue 11/20/13
I'll try buying a few more assasins then. Maybe I just didn't get both
sexes. They're good cleaners and an attractive addition to the tank as
<Sounds like a good plan. Cheers, Neale.>
Not sure if it's the right email that I'm sending this to.
Just a quick note on your page about these snails. I bought 3 yesterday
to get rid of my other snail infestation. Have some cherry and amano
shrimps in the same tank.
When I got to the tank this morning, I found a red cherry sucked
almost dry with one of the assassins still busy cleaning it out.
<Can happen. My specimens seemed to ignore the shrimps, and the
Cherry Shrimps bred merrily away with the Assassin Snails. But the
Assassin Snails are hunters, and they surely can take down a sick/weak
shrimp given half a chance. They will also eat the moults -- don't
forget shrimps cast off a moulted exoskeleton each time they grow. For
the snails, moults are a good source of calcium. What you have there
could very easily be nothing more than harmless recycling of a shrimp
moult into snail shell!>
I don't mind the loss since I've learned something from it.
Have a great day.
<You too, Neale.>
Assassin Snails for Snail Control in Soft
I made a mistake last week. With my last plant shipment I
absent-mindedly added the plants to the tank without a thorough snail
inspection. By the time I realized it was too late and, of course, this
shipment must have had a few snail eggs. I have removed three snails
from the tank already and see snail eggs littered across the glass. My
lfs has assassin snails which I want to use, but my GH is 125 and KH 71
ppm and I know this is soft for snails. My tank already has a school of
Danios and I will be adding a school of cherry barbs after they finish
quarantine next week (although I can hold off on this) so I wasn't
sure about adding shells or something similar to increase the GH. I
don't necessarily want/need to keep the snails and was wondering
how they will do temporarily. I can easily remove them and put them in
a small hard-water tank after they finish off the other snails but, as
I have never done this before, I don't know how long this will
take. I considered adding Gouramis as I saw these will bug snails, but
as my tank is a 20 tall and I already have two schools of 6 fish each
this doesn't seem like a viable option (unless I decide to
permanently keep the barbs in the 10 gallon). I have a couple shrimp in
the 20 tall so I can't use a molluscicide but will definitely use
it for any new plants in the future. I assume if I rinse new plants in
this and then rinse them in plain water I will not need to worry about
the chemicals leaking into my main tank? Any advice would be
<If the water is soft, the other snails should breed only slowly, if
at all, so removal by hand would be the ideal here. If you must use
Assassin Snails, provide a small piece of cuttlebone for them to
consume. You can't stop snail shells dissolving
("pitting") in soft water, but you can at least make it
easier for the snails to grow their shells in the first place. Even so,
these snails will probably do poorly in acidic water in the long term,
and may have a rather short lifespan. Cheers, Neale.>
Clea helena question, + observations
First, my thanks. I'm a card-carrying newbie, but many a disaster
was avoided and even more were mitigated with the excellent advice that
you folks share. It's not all fire-fighting; following your
stocking and compatibility recommendations, even belatedly, has given
me three happy little tanks. Unless something big and heavy gets in the
way, you and my great LFS have spawned another "lifer".
Second, a Clea helena question: Nearly half of my juvenile assassins
have a pinkish-rusty stripe instead of the yellow stripe. I don't
know if they outgrow it or not, since observed it only last week. Water
quality is maintained at NH3 and NO2 = 0, NO3 <15, pH 7.5,
basic-to-acidic, heavily planted tank; plenty of cuttlebone for
nibbling; so I haven't worried...yet...just curious. Diet? (Their
favorite "snello" treat includes ground cichlid pellets.
Possibly snacking on dwarf shrimp mates.)
Genetics? Any cause for worry or caution, that you can think of?
Third, Clea helena observations: Neale M.'s words sold me on these
little rascals, and I've had not a moment's disappointment. May
I add a little to your data, though?
I introduced 3 adult assassins to a 6-gallon, underwater jungle stocked
with 4-5 doz RCS (do dwarf shrimp populations -ever- become
on 1 Apr 2011. Plenty of red Ramshorns and MTS were available for
munching, in addition to goodies the RCS passed over. By June 3,
I'd moved 8 tiny assassins to another tank. On July 5, I moved 6
juveniles to a third tank.
Over the last two days, I removed 40+ juveniles and donated them to
aforementioned LFS, plus moved another 8-10 juveniles to the other two
tanks. I suppose their warm water (78F-80F) may be causing the
grown-ups to burn their snailio candles at both ends, since
reproduction hasn't been that, um, "overwhelming" in the
cooler (74F-76F and 73F-75F) tanks.
Nevertheless, Agamemnon and Clytemnestra have been renamed Trudie and
Sting. Paris is pretty much true to his, or her, namesake (pick
Regarding diet, these over-indulged critters have never, as far as
evidence indicates, touched my MTS or Physa. They will topple
everything and spit out flakes in order to get to a Ramshorn, though,
assuming they beat their Betta tankmate to it. They and/or Betta-buddy
also demolished 50 or so RCS within 2 months. Most fascinating,
however, was observing 4 juveniles in 2 sizes take down a healthy
Tylomelania while he was munching his zucchini treat. Two days later, I
watched 3 juveniles kill one of my 2 Nerites (hey, everybody's got
to eat). And so, while all were lying around burping like
kings-of-the-jungle after the feast, I cleaned house, except for adults
and lurkers, and into the LFS baggie or other tanks they went. Come to
think of it, they have no business, or perhaps too much, in the dwarf
Cray/crystal red shrimp tank!
Because it bears repeating, thanks for EVERYTHING you do, and for the
hours you've dedicated to it.
<Harriet, thanks for your informative e-mail. This is all very
Yes, juveniles have slightly different, somewhat pinkish colouration.
Your specimens seem to breeding rather quickly, but you are keeping
your tank warmer than me (I rarely keep tanks above 25 C/77 F because
so few fish appreciate such warm conditions). While I have seen adults
consume juvenile Tylomelania, they haven't taken down any of the
adults (which in my case are about 2-3 inches long) and they've
never shown the least interest in my Nerite snails. But perhaps my
specimens aren't typical. All extra information is much
appreciated, so thank you! Cheers, Neale.>
Re: Clea helena question, + observations 9/7/11
Thank you, Neale. I'm quite relieved to hear that the pink-to-rust
color is natural, and -not- indicative of mutant spawn bent on world
domination; or, worse, my fault in gross overfeeding.
<If it is a problem, I'm making the same mistake! But they seem
to grow up the regular colours.>
Regarding juvenile hunters, there was no time to photograph the event,
since there was only an instant (in snail time) between "munching
with..." and "munching on'¦."
<Always the problem with predators is telling when they're
hunting and when they're scavenging. They are certainly scavengers
that will eat sick, dying or dead snails as well as most anything else,
including dead fish.>
As the first two assassins, scarcely 1/2-inch shell length, wedged
themselves between the snail (Tylomelania zemis? sold in US as
"chocolate poso") and its shell (smaller than your tylos,
about 1-3/4 inches), it jumped--an exaggerated flinch--then slowly
relaxed. During that time, the "baby", 1/4+-inch, assassins
were climbing the poso's head, one from the sand in front, one
dropping down from the upper shell. Considering my lack of knowledge
and experience, it's hard to tell at that scale if they're
contributing or watching.
In another 60 seconds or so, other assassins were scampering toward the
feast. So maybe adulthood, but not full growth, is reached by the time
the anentome approaches 1/2-inch?
<Sounds about right.>
The trio who appeared to bag the Nerite were all more than 1/4-inch
shell length, but not yet 1/2 inch. Again, everyone was busy tidying up
a squash skin, when the three assassins ducked under the Nerite. The
big snail wobbled a bit, but I thought perhaps it was from being lifted
by little guys that are essentially moving pebbles. The assassins
disappeared underneath, and I might have assumed they dug into the sand
had they not been joined minutes later by a crowd of onlookers, all
sizes, hell bent on a meal. The lot managed to tilt the Nerite shell.
At that point, I had other things to do. Calling my LFS to arrange for
multiple adoptions and a couple of new big snails, to start with.
<Very curious. It's not clear to me how they hunt in the first
place, so possibly they use poison or something else to paralyze their
Considering the level of activity, I have moved/am moving remaining
assassins out of the Betta tank to a cooler one with no intended, live
targets other than MTS and Physa. That tank is heavily planted, also
with a cable heater in the dirt, so there could be already a city of
them under there with empty MTS shells stacked in the corners, for all
I know. However, the plan is to move them out of the fast lane and
warmth of the city lights into something a little more snail-paced.
Thanks again for your various stocking recommendations. As a beginner,
I've found them easy to care for, and first-rate
<They are certainly very fun snails to keep, as are the Tylomelania,
and bring a bit of the "reef tank" quality to our freshwater
systems. It's so easy to watch snails and shrimps doing their
thing, you sometimes forget it's a freshwater aquarium! Cheers,
Assassin Snail Behavior -- 05/07/11
I purchased a Clea helena more than six months ago and
reported to Neale that after at least six months I found a tiny baby.
The strangest thing has happened. I hadn't seen mom in several
weeks but I got up one day to find the entire infestation of rams horn
snails dead. I mean going from at least 50 to 0. I was concerned about
water quality then noticed that there were plenty of rams shells with
no one home. I thought the baby must have finally gotten his
The weird part that got me testing the water is that all the rams from
the floating plastic plants were also gone and I couldn't
understand why they would come down from the floating sanctuary. Then
the leaves on the plastic plants turned a dark purple I assume algae
that is no longer being eaten.
Today I added a couple algae wafers to the tank for the Cory cats to
snack on and guess what? I bet you can guess. I spot THREE assassin
snails and to my utter surprise the smallest one is hanging on to the
floating plant hopefully cleaning it up.
I don't think there's any special concern but I wanted to check
because the food population (of live snails at least) has dwindled. Now
I kind of miss the little nuisance snails that were kept at bay when
there was one snail but are totally gone with three. I assume there
might be some eggs for the rams and maybe there will be a new
generation but it's been at least three weeks. The assassins killed
every single one regardless of size.
One of my Zebra Nerite passed away a few months ago and I guess three
Clea Helena probably equal one of those or not even mass wise. I also
have a feeling that three might not be the max I see over time.
Still, Clea Helena is pleasant to observe which is rare but I know at
least today that the algae wafer got them to show themselves as a
The question is, should I be varying the tank feeding to compensate for
the lack of live treats? I'm assuming they will do OK cleaning up
left over flake and algae and obviously the wafers were
Any feedback appreciated. I'm pretty sure all is well but I like to
check in when there's a major change.
<Hello Greg. Ramshorn snails may well be eaten in significant
quantities by Clea helena. But Nerite snails of larger size than the
Clea helena do not seem to be at substantial risk. Possibly the odd one
might get eaten, but do remember Nerite snails don't always adapt
100% to aquaria. As a ball-park estimate, it seems that out of every
three or four Nerites you buy, one fails within the first few weeks,
while the others go on to live for years. That's been my experience
anyway. I have Nerites and Clea helena in the same tank, and there have
been no Nerite deaths in 3 years. Clea helena do seem to specifically
target small snails, ideally ones less than their own size. They are
scavengers too, so if a snail dies from some other reason, they'll
eat that. You don't need to specifically feed them anything. Their
population will adjust to the amount of food available. In an aquarium
many of the Clea helena will be going for flake food, bits of algae
wafer, bloodworms, krill and so on, as well as the normal fauna of
worms and crustaceans in your aquarium. You don't particularly want
to increase your Clea helena population -- what you want is to build up
your original adults into a stable population that minimises the impact
of pest snails. If you want to add some snails, try Tylomelania snails.
Clea helena will exterminate their babies without problems, but the
adults, which are up to 12 cm/5 inches long, are far too large to be at
risk. These snails are excellent scavengers and I've found them
particularly good alongside catfish, predatory characins and so on.
Despite initial reports to the contrary, Tylomelania appear to be
extremely easy to maintain and are now fairly widely sold under a
variety of names -- Yellow Rabbit Snails, Elephant Snails, Helmet
Snails etc. Cheers, Neale.>
Re: Assassin Snail Behavior 5/16/11
Thanks Neale. I wish I would have been faster on the camcorder because
one of the "2nd generation" Clea helena appeared to go after
one of the Nerites last night. It was quite exciting for about 5
minutes. When on the sand the assassin seemed to be trying to scoop his
horn under the belly of the Nerite. Have no idea if the Nerite actually
sensed danger or not but to get away he went onto the glass side. The
assassin gave up after about a minute following on the glass.
Doesn't seem to be in real danger. First time I saw any such thing
and I guess with the armor there isn't much to worry about.
Who knows what damaged could have been caused if any as long as the
Nerite keeps moving. The Nerite is several times bigger than the
<Yes, I think after a while the Clea end up ignoring the much larger
Nerites. But "your own mileage may vary" as they say. Nerites
are pretty cheap here, so even if I'm wrong, there's not much
I found "mother" Clea helena today for the first time in
weeks. She seems fine staying buried most the time. When it was just
her the Ramshorns were held at bay at maybe 50 or so tops at hatching
season but now they are completely gone. I counted FOUR assassins
today. It appears to be three different generations based on size.
<Agreed, this is what I tend to see. Clea helena is a slow breeding
species, but under good conditions does breed steadily.>
I don't know that much about their reproduction but it seems
"mom" came in with a fertilized egg and now these two have
mated to create two more specimens. I understand they are slower than
the Ramshorns but they seem to be going about it pretty quick at this
point but of course have killed off the meaty part of the food
<At some point food will becoming limiting, and because they're
carnivores rather than herbivores, the upper limit on population size
is likely to be less per gallon than, say, Ramshorn snails.>
I want to make it clear that this increase in Clea helena population
wasn't intentional. I brought home 1 specimen and now I have 4. The
first one entered the tank in early November 2010 and the second one
was spotted in March of this year. I wonder now if the two newest that
I've spotted (and by far the smallest about the same size) were not
a breed from between first and second generation and were left over
from the original eggs that may have come home with mom. It seems four
months for the first baby to be seen and two more for the second two.
Two months seems rather fast and spells trouble unless I get into the
breeding business but like you said the environment should sort it
<It will, or you can always remover surplus snails and sell them.
There's a good market for Clea helena.>
With regards to what you said about adding Tylomelania, I assume you
mean if I'm interested in another snail species and not to add them
as a food source. Honest, I'd be happy with just the Nerites and I
only added one assassin to keep the Ramshorns at bay. I didn't want
to kill them all off because I was worried about what to feed the
assassin afterwards. Now I have four instead of one but no Ramshorns. I
assume though your advice overall is not to sweat it.
<Quite so. In all my tanks they seem to level off at a population
where I'll see a couple or three if I hunt about, but no more than
The only other odd side effect is that certain species seem to stake
out their favorite areas. With the Ramshorns gone an area of black sand
now has a green tint to it, I assume because the Ramshorns aren't
there to till the soil. The catfish don't seem interested in that
section of the tank for some reason and the sand just isn't churned
<Curious. The Clea helena at least are excellent
PS: My Trichogaster leeri male is doing the sand thing again. This time
he's actually building his first bubble nest. I am supposing last
year when the females were about half his size that either he
wasn't old enough to understand his dad duties or the females
weren't ripe enough. He is SUPER ORANGE now. Much brighter than
The sand thing is interesting and I haven't seen it documented
anywhere else. He scoops sand up from the bottom and dumps it on
whatever is under the bubble nest. That used to be a cave which
confounded me for days since I knew the filter wasn't doing it. Now
there's 10" tall plastic tries that he's coating with
<It is odd behaviour. Normally, these fish cement bits of floating
plant debris into their nests.>
Life both out of and inside the tank are fascinating.
<Sounds to be the case! Cheers, Neale.>
Assassin snail eggs? 4/4/2011
I have a twenty gallon tank with a single female Betta, 3
assassin snails, and I just added 6 glass or ghost catfish.
Two of the assassin snails were crawling all over each other for
almost a half a day and the next day I found about 10 little
spots on the glass that look like sacs with something inside.
They're about 1mm.
I've included a pic but I'm sure if you can tell from
My question is can I use a gravel cleaner in there or will I take
a chance on killing some of them? How long will I have to
<Hello Tim. Clea helena lay eggs in transparent, sachet-like
capsules about 1 mm across. They tend to be dotted about on hard
surfaces, far apart rather than in clumps. Once they hatch, the
baby snails dive into the substrate, so yes, you want to leave
the substrate alone. I've only kept them in tanks with sand
-- in the wild they burrow into sand and silt -- and the juvenile
snails reappear at shell lengths around 5-6 mm long,
usually several months later. I wouldn't keep them in a tank
with gravel given their ecology. In any event, using a gravel
cleaner is generally pointless so I'd lay off if you want to
breed these snails. In a sandy tank you don't ever use a
gravel vacuum, the snails cleaning the sand all by themselves.
|Re: Assassin snail eggs? 4/4/2011
The substrate is mostly the smaller material for growing plants. I
wasn't planning on breeding them but it happened. Should I try
and make a sandy area for them?
<Wouldn't bother for now. See what happens!>
<Do have some personal observations here:
Clea helena New Baby 3/15/11
I know I don't have a perfect track record of identifying new born
snail species (I brought home pests on plants and had no idea back
then) but I'm sure I'm right on this one. I have a new baby
<Cool! They breed rather slowly, but yes, they do breed.>
Thing is, I only had one since November 1st. I haven't seen
"mom" for a bit but that isn't unusual.
There's plenty of empty Ramshorn shells that shows the job is being
taken care of. This new snail though is extremely tiny.
<Yes; a couple of mm long, with a small brown shell, sometimes with
the yellow stripes visible.>
So even though I haven't seen both together, there's no way
it's the same snail. I'm talking about the size of a baby
Ramshorn. I would never have seen it if it wasn't on the glass and
it is so small I'm surprised it wasn't eaten.
<Somehow they survive!>
I'll get a picture later after the camera charges. I just
didn't know how unusual this is to start with "one" and
four months later have two. I know this is a rather new to the trade
creature so I wanted to share my discovery.
<Thanks for sharing. Mine do breed, and to a degree, you should end
up with a stable population. Better still, they help to keep pest
snails in check.
Clea helena New Baby
<PS. I have a photo of a young Clea helena about halfway down this