This is a post for anyone in doubt of the effects No-planaria (Betel Nut extract) and similar dewormers have on snails.

I accidentally exposed my Mystery and Rabbit snails to a single, full-strength dose of No-Planaria for 24-36 hours. I had previously operated under the assumption it was only harmful to Nerites; wrong! After that time the mentioned snails were all completely withdrawn into their shells and appeared to have absolutely given up. After 2 days of moving to untreated tanks, air baths, highly oxygenated breeder boxes with carbon and Purigen they are finally starting to come around.

As an aside, the Ramshorns took zero issue with the NO-P treatment. Stick to traps unless absolutely necessary, as the tank is now unsafe for these snails for at least 4 months.

In this Reading:

Ecology of the NZMS, and its threat to local waters

How to distinguish NZMS form Malaysian trumpet snails

Why you should care, legally and ethically, as an aquarist

Prevention and removal from your aquariums

What to do if you see them in a store, or get them in a shipment of plants

iNaturalist gallery:

https://www.inaturalist.org/taxa/129201-Potamopyrgus-antipodarum/browse_photos

Introduction

In the months leading to writing this, I have noticed a drastic increase in the number of posts on aquatic snail subreddits asking for snail ID, and pictured is the highly invasive New Zealand Mudsnail (Potamopyrgus antipodarum), or the NZMS for short. They are coming with plants in local fish stores, and, according to some replies, even being given away to unknowing customers by unknowing employees.

Not only is it illegal to spread these snails, it can have catastrophic effects for local waters. In my area, they have found their way into a large number of waterways, and many areas where they are not yet present connect to infested waters. There are currently no removal methods for them, only preventing introduction. My hope in writing this is to spread the word about this invader in the hobby, and hopefully help slow its spread in our tanks and waters.

Ecology of the NZMS

These snails, as their name suggests, hail from New Zealand, where they grow to about 12mm. In their invasive populations, they grow to only 4 to 6 mm in size. Invasive populations are all female, and parthenogenetic, meaning a single snail can create clones of itself without another present. While this is true for a few common aquarium snails, these invaders reach staggering densities, with a population in Sweden reaching up to 800,000 individuals per square meter. On the bright side, they are livebearers, so we don’t need to worry about eggs.

In their native range, they are controlled in number by several parasitic flatworms, which sterilize infected individuals. In their invasive ranges, they have no natural predators, and are even capable of surviving being eaten, with one study showing they can survive 12-24 hours inside a rainbow trout. They do this by sealing off their operculum, a strategy that unfortunately also works to resist chemical treatments like bleach.

Their diet consists primarily of biofilm and algae, and due to their high reproductive capacity, they outcompete native invertebrates that occupy the same niche, with some populations becoming 95% of the invertebrate biomass. In other words, the organisms that depend on these communities for food, can have their food supply reduced by up to 95%, and the invertebrates that once occupied that niche will also be drastically reduced in number.

Identifying the NZMS

The main snails these will be confused with are Malaysian Trumpet Snails (Melanoides tuberculata), or MTS for short. Courtesy of u/Gastropoid, a moderator of r/AquaticSnails, Figures 1 and 2 are some pictures comparing the two.

Figures 1 & 2: Comparison of NZMS and MTS

The main differentiating factor is the maximum size, with NZMS never reaching over a cm in length. Additionally, the MTS have many striations/grooves on their shell whorls, and often some red patterning, where the NZMS is largely smooth and plain. Color can vary from tan/grey to black for the NZMS, and some populations have developed slightly different shapes to their shell, such as spikes or a keel on the whorls (Fig. 3). NZMS typically have 7-8 whorls, whereas MTS often have up to 10-15, though juveniles may have less in both species, making differentiation hard in overlapping sizes. There are other similar species, but the MTS seems to be the most common confusion in aquariums.

Figure 3: Alternative phenotype

If you are at all uncertain as to the identity of your snails, DO NOT add them to your tank. Quarantine, get a nice closeup picture with a ruler, and ask for ID from one of the aquatic snail subreddits, or another reliable aquatic snail/aquarium forum. 

It’s just a snail, right? Can’t their population be managed like any other in my tank?

The short answer is no, not really. As stated earlier, these will outcompete any other invertebrate in the wild. This applies to the snails and shrimp in your tank as well. They are extremely efficient grazers, meaning you can’t really control them by controlling the food. They will proliferate as long as there is any biofilm in the tank. 

They also pose a significant ecological, and potentially legal risk as long as they’re in your tanks. It is illegal to knowingly distribute or introduce this species in many states in the US, and consequences include some hefty fines, even jail time in some cases. 

So if you just keep them in your tank with no escapees, it’s fine, right? Not really. Many states have bans on possessing the snails at all, and since they exist in your tank, it’s possible they’ll be spread by you. It could be on plant trimmings, in your nets, even down the drain; I’ve even had some on my arms after sampling an infested stream.

The point here is there is no acceptable amount to knowingly harbor, and they cannot be allowed to exist in the hobby as “just another snail.” I love all snails, like many of you reading this, and would never condone harming them in an aquarium, but these will cause irreparable harm to our native aquatic ecosystems, especially the native snails. There is no removing them once they invade, only containing and limiting spread.

If that was not enough to convince you, let’s look back a few years at marimo moss balls. They were banned entirely due to them spreading zebra mussels, another aquatic invasive species. Additionally, the spread of Chytrid fungus has led to restrictions on the amphibian trade. If things continue to progress at this rate, there’s no telling what kind of restrictions might be imposed. It’s possible there will be none, but it’s also plausible all snails will be banned, as in the case of crayfish in Pennsylvania.

How do I keep them out of my tanks?

Removal is a meticulous but doable task, so prevention is key, but there are few viable methods. They can survive just about any chemical treatment that is safe for your fish, shrimp, and plants. This includes prolonged exposure to bleach, hydrogen peroxide, and even fenbendazole, which is sometimes used to treat hydra and planaria infestations, often killing snails as well. I have not heard any conclusive results for copper and planaria-zero as of yet, but copper will also make your tank unsafe for invertebrates for a very long time. The USGS and many state agencies recommend quaternary ammonium compounds (QACs) found in cleaners like Formula 409 for fishing gear, but these are not safe for aquarium use. 

ETA: Salt is likely ineffective, as they can survive even brackish estuaries. Vinegar doesn't seem to have been tested much. Alcohol is also a mixed bad, and not worth considering outside preservation in 70% ethanol.

Several abiotic treatments will kill them. Obviously, a firm finger on a hard surface to flatten them will work, but do be careful. The embryos inside are extremely small, and potentially viable. Freezing solid for at least 4 hours at 26F/-3C, as well as hot water of 120F/46C for 10 minutes, with longer preferred, can kill them. Drying in a low humidity, preferably hot environment, for at least 48 hours is recommended for fishing gear, but they can live over a month on moist surfaces, so use this method with caution. Ensure ALL surfaces are COMPLETELY dry for well over 2 days, and always use drying in conjunction with a guaranteed lethal treatment when possible. While not useful for prevention in plants, these methods are viable for nets and nonliving materials.

Additionally, certain water parameters seem inhibitory to their reproduction. Low TDS and hardness, fast currents in streams, and an acidic pH all make it hard for them to establish. While none of these can prevent a tank infestation, it can certainly slow them down a bit.

Many have recommended biological control such as assassin snails, puffers, and loaches. This is not a remotely sure method of removal. They can survive digestion by the loaches and larger puffers, and smaller predators like pea puffers and assassin snails, assuming they eat them at all, will never eradicate them. Given their small size and lack of “meat”, they aren’t really eaten by these predators to begin with. Remember: one will make more, and it is usually illegal and always ecologically irresponsible to harbor and/or distribute ANY quantity of them. There is no “safe” amount.

Another method often used when dealing with unwanted snails is baiting. You add food, wait for them to swarm, and remove them with it. This will not work, as it will also never get them all. It will only temporarily lower their numbers.

A method that does show promise is reverse respiration treatments. I reached out to the authors that pioneered the method on their website, and while they didn’t test it with NZMS specifically, they told me it had a 100% mortality rate in MTS, where even bleach failed due to their tight fitting operculum. I also have used it on plants from an infested stream and it seems to work well so far, with my few trials having complete mortality of the NZMS. The website explaining the method is here: https://reverserespiration.com/. It sounds complicated by the name, but it really only requires some unopened and in date carbonated water, a container, and 12 hours of darkness.

Even with an effective treatment, quarantine plants for an additional 2 weeks to ensure no surviving hitchhikers are present. It is possible the treatment had survivors from a number of potential errors, including old carbonated water or incomplete submersion.

Additionally, since they survive the digestive tracts of fish, quarantine all new arrivals in a bare bottom tank, observing their feces for any snails. The amount of time to do this varies by fish, but quarantine should generally last a week or two at minimum anyway, so that should be plenty of time. Extend the quarantine if live NZMS are observed, as the fish may re-ingest them. 

I have also seen them hiding in the shells of larger species of snail. For this reason, it is imperative you quarantine snails as well, not just fish.

It is also worth noting that it is very easy to miss them on yourself. They can stick to your arms, under your fingernails, or even between your fingers. I’ve had some in my hair while out sampling from swatting a bug on my head. Make sure you don’t reach into a tank without washing your hands thoroughly in a bucket/bowl and checking for NZMS. If there are some, apply a lethal method to them and throw them in the trash.

Note: “lethal methods” are hot, cold, and crushing, as well as reverse respiration. Utilize at least one method before disposing of them.

Okay, but they're already in my tank; what now?

First, don’t panic. This is fixable, but it’ll take some work, space, and a few supplies. The long story short: you need to ensure all surfaces and water that even potentially had NZMS are exposed to one or more of the above mentioned 100% lethality measures. In our case, we’ll stick to reverse respiration, freezing, and hot water.

Notify any places you recently added animals or plants from that you found them in your tank so they can inspect their own facilities. In the guts of fish and on plants are primary transport vectors for the NZMS.

We’ll start with the bad news; you’re going to need to break down your tank entirely, and likely have to replace a few things, at least short term. The good news: summer and winter will work in your favor here, as they will give you the temperature extremes needed to kill the snails, either outside in the freezing cold, or in the back of your car in a hot parking lot. 

A few things to remember before I go further: these snails can be eaten by your fish, and they can survive. This means you need the fish to be able to poop out any eaten snails before adding them to a new tank, or into the original tank after decontamination. I can tell you from personal experience, you want to be thorough, or you may have to do this all again. 

Additionally, you should always assume any surface in contact with the tank or its water, or anything in it has NZMS, and NEVER cross contaminate with these things. THIS INCLUDES YOUR HANDS!!! Apply a lethal method to all of them before use again. The babies are very small, and can easily be glossed over in a hurry.

Lastly, NEVER dump live snails down the drain. It isn’t worth the risk that they find their way into local waters during the path to and through the water treatment and discharge process. 

Now, on to the process at hand. Get a tank, bucket, or something that can house your fish for a week or two while you work on the main tank. Add a NEW filter, and some beneficial bacteria. This can be bottled, or it can be from squeezing a filter you are certain had no possible NZMS invaders. Add all of your fish, and nothing else. Pick a material the snails will stand out against, as we need to observe daily at minimum to ensure no NZMS came out.

You will need to monitor water quality closely for ammonia and perform regular water changes during this time, as we cannot truly cycle this tank in the short time before we add the contaminated fish. Alternatively, you may cycle it ahead of time, but assume all water and objects used in or leaving the original tank are contaminated in that period, and apply lethal methods before using them elsewhere.

Take all of your plants out, and wash them in a bucket of tank water, manually removing as many snails as possible. You can treat them all, but personally I take cuttings of what I can, and then salvage as many crown plants like swords and crypts as possible. These plants will all be treated with reverse respiration, so grab a few containers and a bunch of seltzer/club soda, and treat them that night. Once treated, rinse in a bucket of clean water, and add to another bucket separate from your fish. We don’t want any snails coming out of the fish and onto the plants. 

To dispose of water, do not dump it near any body of water or down the drain. Separate the solids out of the water, and freeze for 4 hours or soak in 120F water for 30 mins, then throw them in the trash. Water can be dumped in the grass, but make sure there are no storm drains, ponds,  streams, or any potential introduction hazards nearby, such as flood zones, to be safe.

Now onto the tank. Drain it, disposing of the water as mentioned above. The substrate is best placed in a garbage bag, frozen, and thrown away. This can be done in batches. Alternatively, near-boiling water can be poured on it, but do be careful. A pot of boiling water is both heavy and hot. It can hurt you. NEVER boil or bake large rocks! If they have air pockets internally, they can explode, and rock shrapnel is never fun. If you wish to keep the substrate for any reason, it must be dried after freezing or boiling water for several months. Make sure it is bone dry for at least a month. If you do not wish to keep it, either throw it in the garbage, or bury it in a place that is nowhere near water or could wash into any, after it is dry. Make sure a lethal method has been used prior to doing either. Rinse the tank and dispose of the water as directed above. Allow it to dry thoroughly and remain bone dry for at minimum 48 hours, then vacuum/wipe it out, immediately putting the dirt and/or towels in the garbage.

Wash your lid in scalding hot water, and dry in a low humidity area for at least 2 days. Dispose of the water as directed above. The light should be fine, but it won’t hurt to give it a once over. Filters, heaters, and any other equipment should be soaked in hot water of 120F or above for 30 minutes, or frozen, and all filter media discarded after freezing and replaced. Dispose of the water as described above. Make sure the equipment can handle the temperature you choose to use.

Now your tank should be completely deconstructed, and all your equipment and tools used in the deconstruction are treated and drying. After the 48-72 hour drying period, set up the tank as normal. During this period, monitor the fish in quarantine, regularly vacuuming the bottom of the quarantine tank and scalding or freezing it before disposal. We want to make sure all NZMS are out of their system. If you find any NZMS with the fish, remove and kill them immediately, and extend the quarantine until none are present for a week. This is excessive, but necessary to guarantee they haven't eaten the snails again. A snail trap in the tank with them could prove useful during this time to easily detect the snails. Once the fish are clear, add them to the tank again, and decontaminate the quarantine setup with the applicable methods from above. 

You should now be free of the NZMS. Congratulations, and thank you for your diligence. It was hard, but worth it in the long run. Make sure to quarantine all plants in the future, treating with reverse respiration in the process, as well as any fish you buy. Not only is it good practice to begin with, it will save you many headaches in the future.

They’re at my LFS/They came with my plants. What should I do?

First and foremost, notify the owner with as much information as possible, and let them know what they are dealing with. Feel free to share this reading with them for methods of removal and quarantine. Check back in a week or two, and see if they eliminated the issue. In these instances, they shouldn’t sell anything from the contaminated system, especially plants, effective the moment you mention the invasive snails, or they will aid in their spread. Make sure to note the similarities to Malaysian trumpet snails when discussing it, as many confuse the two, and both can be present in the same tank. If they are baby MTS,that’s great! But it’s not worth the risk that they aren’t, and a positive ID should be gotten.

Additionally, proactively notify your LFS! It’s clear the snails are coming from plants from what I’ve seen on Reddit, and many LFS owners I’ve spoken to were unaware it was happening, and thanked me for the head’s up. Prevention is key!

If the owner or management haven’t taken steps to remedy the issue, you unfortunately must report it to your local aquatic invasive species agency. Who handles it varies by state, but a quick google search should tell you who to contact. It’s never fun to have to do this, but these stores are responsible for what they sell, and you will have given them due courtesy to solve the issue beforehand. With online retailers, I personally would notify the state agency they fall in the jurisdiction of after the issue is resolved as well, or ask them to get an inspection. If they truly remedied the issue, there won’t be any trouble for them, and it may help your state agencies know if there are contaminations further up the supply chain.

Some parting words:

Thanks again to u/Gastropoid on Reddit for the photos and information contributions, and to the many other Redditors that provided valuable information on their encounters with these snails. Many thanks to the team behind Reverse Respiration for their hard work and valuable contributions to the hobby, as well as the information they provided on the method for NZMS. 

Last, and certainly not least, thank you. I truly appreciate you taking the time to read this. I encourage you to share this valuable information to as many people as you can, especially your local fish stores, to aid in preventing the spread of the NZMS in our tanks. If you have any questions, feel free to reach out to me on the site this is posted, and best of luck on your aquarium journeys!

Further Reading/Sources Used

Bruce, R. L., Moffitt, C. M., & Dennis, B. (2009). Survival and Passage of Ingested New Zealand Mudsnails through the Intestinal Tract of Rainbow Trout. North American Journal of Aquaculture, 71(4), 287–301. https://doi.org/10.1577/A08-033.1

Geist, J.A., Mancuso, J.L., Morin, M.M. et al. The New Zealand mud snail (Potamopyrgus antipodarum): autecology and management of a global invader. Biol Invasions 24, 905–938 (2022). https://doi.org/10.1007/s10530-021-02681-7

National Park Service:

https://www.nps.gov/yose/learn/nature/invasive-animal-species.htm

NZMS Collaborative’s ID Guide:

https://www.nzmscollaborative.org/index.php/nzms-basics/biology

Oregon State University (Includes AIS Treatment Effectiveness Table):

https://www.dfw.state.or.us/conservationstrategy/invasive_species/docs/NZ_Mudsnails_10-page.pdf

Reverse Respiration Treatment:

https://reverserespiration.com/reverse-respiration 

UC Riverside Center for Invasive Species Research:

https://cisr.ucr.edu/invasive-species/new-zealand-mud-snail

USGS NAS (Non-Indigenous Aquatic Species):

https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=1008