Ask any aquarist to rattle off a list of their most dreaded pests, and you’ll find vermetid snails. These invertebrates wreak havoc on reef tanks in no time at all. Even worse, trying to find and eradicate them can pose a challenge. Good thing you have this handy primer to everything “worm snail!”
Table of Contents: Vermetid Snails
“Know thy enemy.” Odds are, if you’re coping with an infestation of vermetid snails, you want to jump straight to ridding yourself of the freeloaders. And you’re free to do that. But when it comes to pests in an aquarium, a thorough understanding goes a long way. So consider reading through the entire article, so you know where those pesky snails came from in the first place (not to mention how to bar them entry).
What Are Vermetid Snails?
Any time you introduce corals or live rock into your display tank, you run the risk of hitchhikers. Sometimes those freeloaders end up beneficial (for instance, a feather duster you never knew you wanted around). But other times? You find yourself playing host to pests that quickly take over your tank. Vermetid snails fall into the latter category. And like Aiptasia, they’re pretty happy to take advantage of the resources you’re providing, thrive, and reproduce in enormous numbers.
Vermetid snails belong to the Vermetidae family. And there are over 160 different species throughout the tropical and temperate bands of the ocean. (Yeah, they’re THAT successful) They hang out within coastal zones attached to sponges, corals, and any hard surface that might keep them near a ready food source. You’ll catch them in the company of other filter feeders, pulling in particulate-sized pieces of plankton and detritus.
But it’s easy to overlook vermetid snails – even the largest members of the group, which come in at a whopping 4 inches (10.2cm). Because these mollusks don’t look like your typical snail – not as adults, anyway. And that’s the key to their success. They slide under the radar. And by the time you realize you have a problem? It’s too late.
When is a Snail Not a Snail?
What do you usually picture when you think of a snail? A spiral shell. That’s the expectation. And even most marine snail species form traditional, spiraled shells. But vermetid snails break the mold when they settle as adults.
If you catch a glimpse of a juvenile vermetid snail, you might dismiss it. The free-roaming infants get confused for cerithoids ALL the time (when you CAN see them, anyway). They swim around the water column, looking for the perfect hard surface to attach to. And that’s the end of their spiral-shelled existence.
Vermetid snails form calcified tubes rather than mineralized shells. The tubes look a lot like the structures built by tubeworms. (This is why you also see them referred to as “worm snails” or “worm shells”) The pale tubes lack any colorful ornamentation. Instead, you’ll get dark growth lines. The snail CAN break the tube down and reshape it, allowing them to curl around the spot they’re attached to. It keeps them competitive in areas where the property’s at a premium.
For some species, you’ll see an operculum at the top – the entrance of the tube. The reason it isn’t a mandatory feature is that vermetid snails don’t live within the tubes. Nope – it’s simply a part of their feeding structure. The snail lives at the BOTTOM. Where the tube attaches to the sponge or coral? That’s where you’ll find the vermetid snail.
That sneaky adaptation allows vermetid snails to slink under the radar. Aquarists catch a glimpse of a “worm” and dismiss it as a tubeworm or even a polychaete. Meanwhile, the snail’s establishing itself in the tank – and starting to cause problems.
Beware the Mucus Net
Vermetid snails don’t travel around the reef. When they anchor that tube shell? It’s permanent. (Yes, they can do some remodeling, but they don’t pack up and move) But since they hang out with other filter feeders in the coastal zone, they don’t NEED to move around. Everything they need comes straight to them, courtesy of a mucus net.
Vermetid snails spit out delicate nets of mucus from the ends of their tube shells. And – like a patient fisher – they wait for food particles to catch on the net, courtesy of the current. The net remains out for around 30 minutes at a time. Then the vermetid snail reels it back in and feeds on the collected plankton, algae, and other detritus.
The coastal zone with its current is the key to the success of the mucus net. Still stagnant water? It doesn’t work. Food won’t go into the net, and the vermetid snail will starve. Scientists have noted that some snails don’t even bother to produce nets when placed in calm water. And that means the end of the road for that individual, as the mucus net also works for reproduction. (Yup, it’s a two-for-one deal)
Remember, vermetid snails remain stationary. And they’re not about to share a choice piece of sponge with another snail. So reproduction needs to happen over distance. Luckily, the mucus net can catch anything – including gametes. Males release their spermatophores into the current. When they catch on a female’s mucus net, she’ll transfer them into her mantle cavity with her mouth. The mantle cavity houses egg capsules, each capable of holding up to 40 embryos (depends on the species). She then releases the fertilized eggs.
Boom! A new crop of vermetid snails to colonize available sponges, corals, or live rock. Say, the surfaces in YOUR aquarium.
The thought of mucus nets crisscrossing your display tank like Spider-man gone crazy probably makes you a little queasy. But are vermetid snails THAT much of a pest problem? Actually, yes. And once you start to notice their presence, you’ll understand why.
The tube shell continues to grow with the snail. That means you’ll start to notice damage to the skeletal structure of your LPS and SPS corals within the tank. The tube can even prevent the coral from growing (they ARE built from calcium). It’s important to look for those spiral structures on the hard surfaces throughout your tank. But concentrate around the highest regions of water flow. That’s where vermetid snails will look to settle.
But the problem doesn’t stop there.
Vermetid snails extend their mucus nets. The nets don’t contain harmful substances, but they can cover plenty of territory. We’re talking anywhere from 1-4 square inches (3-10cm2) of room, depending on the species. The net CAN smother coral polyps, forcing them to retract. Not to mention that the nets will collect the same particulate foods your corals are looking for. Suddenly, your corals start to die, lacking the ability to compete with the vermetid snails.
You’ll see areas of polyp recession. And you may even catch a glimpse of a mucus net in action. The fine threads resemble a trail of – well, mucus. You can trace it back to the opening in the tube shell. And if you follow the spiral to the base? You’ll catch a glimpse of that vermetid snail.
Preventing Vermetid Snails
Vermetid snails THRIVE in pet stores. They hitch a ride on live rock, and the stores don’t always perform quarantine or decontamination procedures. If you look carefully, you’ll see miniature snails drifting through the water, hunting for the perfect spot to settle. This is why it’s on YOU to do the work and ensure you’re not setting your tank up for an infestation.
Of course, you also need to keep in mind that vermetid snails are HARDY. (Think about their natural habitat) They can tolerate a range of water conditions and survive. You’re going to need to exercise patience to prevent the pests from getting into your reef tank.
Any corals or live rocks you plan to add to your display tank need to undergo quarantine. And not for a week or so. You need to plan for AT LEAST a month. This will give you plenty of time to conduct searches for vermetid snails. If they appear? Then you can remove them and prevent an infestation from surfacing in your display tank.
Juvenile vermetid snails look to settle within 24 hours, and they begin to transform to their adult shape within another 2-3 days. If you keep that timeline in mind, you’ll know when you need to check for tube structures.
Treating Vermetid Snail Infestations
Okay, so you have vermetid snails. You DON’T want them to hang around and start reproducing throughout your tank. (Or maybe you’re already at that stage and tearing your hair out) You have options for eliminating this pest from your tank. But each comes with pros and cons. So think through things carefully and figure out what will work best for you – and the rest of your aquarium.
If you’re only dealing with a few vermetid snails (say, while in quarantine), you can physically remove the buggers. Lift out the coral the snail is attached to FIRST, though. You don’t want to allow any of the mollusk to fall back into the water.
To get that snail out, you’re going to need some tools. That tube shell is no joke:
Bone cutters allow you to pries the vermetid snail from coral or a frag plug. You need to go for the BASE of that tube shell, though. That’s where the snail lives (if you remember). If you only cut away the tube, your snail will rebuild. (Be careful when using bone cutters – they aren’t called that for fun!)
Using an ice pick requires a little more precision – to avoid injuring yourself. But it works if the snail’s wedged into a crevice of live rock. Again, you need to remove the piece of live rock from the water. Then stab the pick into the base of the tube shell. Carefully wipe the tube away and ensure you got the snail (otherwise, you’re reintroducing it to the tank).
For aquarists queasy about assaulting even vermetid snails, you can go passive with your eradication. Sealing the entrance of the tube shell with superglue will prevent the snail from sending out its mucus net and obtaining food. That means eventual starvation and death.
Now, you need to prepare for the nitrogen spike when the snail dies. If you don’t, you could end up with an algae bloom. And if you’re contemplating a horde of vermetid snails? This probably isn’t a good idea. You’ll end up with a severe nutrient spike.
You don’t want to use tools, but you’d also rather not introduce superglue to your reef tank or deal with a sudden, rapid die-off. That’s when you turn to Coral Snow for your vermetid snail problem. You’ll reduce the amount of particulate food available by clarifying the water. Without the ready food source, the snails will die off slowly rather than all at once. And the Coral Snow will help balance the nutrient load in the tank. It’s a slower method of treating vermetid snails but effective.
Of course, you’re also going to end up depriving your corals of their usual food source. Unless you want to watch them die, too, you’ll need to target feed them. Depending on how many corals you have in your reef tank (and the species), this may eat up your schedule.
Nature is always in a careful balance. You’ll see predators and prey keeping an ecosystem in check. And you can attempt the same natural “housekeeping” in your reef tank for vermetid snails. The following species snack on these mollusks:
Unfortunately, while vermetid snails show up on the menu, they don’t dominate it. And, given the option, these species WILL devour other food choices ahead of the pests. Then you may end up with a new addition to your reef tank that’s nice to look at but not particularly useful. And if you don’t account for the added biological waste, you may have a new problem.
It’s a gamble that may or may not pay off. But if you have the room in your aquarium? It may be worth the risk.
You’ve reached your limit. Vermetid snails are destroying your corals and taking over your tank. It’s time to employ the “nuclear” option for eradicating the pests. Recognize that you need to hit DESPERATION to go this route. Because you’re going to lose a good chunk of the helpful bacteria in your tank. Not to mention the live rock, sponge, or coral the vermetid snails are attached to.
To push the red button, you’re going to need:
- Eye protection
- Hydrochloric acid (10-20% solution)
That’s right; you’re dealing with an acid that’s harmful to YOU. As such, you need to take precautions to keep yourself safe. DON’T work inside the house. Take your eradication project outside. That way, you have proper ventilation.
Find the rocks, sponges, and coral the vermetid snails attached and remove them from the tank. With your safety gear on, wash the structures in the acid solution. Better yet, allow them to soak for a few days. You’ll know it worked because they’ll bleach white (and all living material will dissolve OFF). Rinse the rocks thoroughly in distilled water to remove the acid and then let them dry before returning them to the tank.
For More Information
Vermetid snails remain one of the banes of aquarists. And thoroughly understanding this pest can help you arm yourself for the battle to come. Good thing you have plenty more to learn!
Such as this YouTube video explaining even MORE, you’ll want to know about vermetid snails:
Or how about this one, which includes even more on removing the pests:
Maybe vermetid snails AREN’T your problem. You can cope with other hitchhikers when you add live rock or coral to your tank. And dealing with these pests can drive you up the wall if you don’t prepare:
If you think about them from an evolutionary standpoint, vermetid snails are kind of cool. They’re not like your garden-variety snail (yes, pun completely intended). Even scientists aren’t sure what to make of them and their tube shells. And, seriously? Mucus nets? Awesome.
But when vermetid snails infiltrate your reef tank, they lose cool points. They can destroy and impede the growth of your corals. And in no time at all, you have an aquarium crisscrossed with mucus nets. This is why it’s essential to quarantine ALL coral and live rock for at least a month. And have a battle plan in case a vermetid snail shows up. (But maybe stay away from the nuclear button if you can)
- Abbot, D.P. and Haderlie, E.C. 1980. “Pseudobranchia: Marine Snails” in Morris, R.H., Abbott, D.P., and Haderlie E.C. Intertidal Invertebrates of California.
- Kohn, A.J. 1983. “Feeding Biology of Gastropods” in Wilbur, K.M. (ed) The Mollusca.
- Shima, J.S., Osenberg, C.W., and Stier, A.C. 2010. “The vermetid gastropod Dendropoma maximum reduces coral growth and survival.” Biology Letters.
- Strathmann, M.F. 1987. Reproduction and Development of Marine Invertebrates of the Northern Pacific Coast.