Vermetid snails: how to get rid of them

Quick reference

What are vermetid snails?

Vermetids look like tube worms but are snails: stationary gastropods whose shells are cemented to hard surfaces.^[2] Reef Builders' Michael Paletta says they arrive on live rock and coral plugs, grow quickly and breed like rats, and blames the recent increase on more coral feeding, more maricultured colonies on pest-prone mounts and better husbandry that keeps hitchhikers alive.^[1]

How to get rid of vermetid snails

Paletta's options, roughly in order of effort:^[1]

Cut the tubes. Snip each tube near its base with pliers, forceps or cutters; fish may eat the exposed snail.^[1] Sealing the opening with superglue also works but often comes loose before the snail dies;^[1] Reefs.com lists gel superglue or reef-safe epoxy, and injecting caustics, with lye (sodium hydroxide) preferred to acid around calcareous rock.^[2]

Take the piece out. Remove the rock or coral, clip the snails, treat the holes with vinegar or mild acid, rinse and return it.^[1]

Starve them. For a tank-wide outbreak, Paletta stops frozen foods such as mysis and feeds only a good flake food; for the first week he blasts detritus off the rock twice a day to make them cast nets, then doses calcium carbonate onto the nets, because the snails can't pick what sticks to their nets and fill up on inert powder. He uses 2 tablespoons per litre of tank water as the stock, applying half twice daily in week one and once daily for three to four more weeks, sometimes up to eight, shortly before lights out, and keeps going for two weeks after they seem gone, since small ones in crevices, overflows and the sump repopulate the tank. Empty tubes mean it worked.^[1]

How they feed

They cast mucus nets from the ends of their tubes that catch plankton and detritus.^[2] Bigger snails cast bigger nets and irritate corals further from the tube.^[1]

Why it's a problem

The nets irritate the corals they touch, and untreated irritation can kill them.^[1] The damage is measurable: in experiments published in Biology Letters in 2010, the vermetid Dendropoma maximum cut coral skeletal growth by more than 50 % and colony survival by up to 40 %, and wild snails were found near dead coral more often than living coral.^[3] Reefs.com adds that the nets help corals' algal competitors; in one field study herbivorous fish were up to 450 % less likely to graze algae where vermetid nets were present.^[2] They also compete for space and clog plumbing in high-flow areas.^[1]

What eats it

Reefs.com says there are no proven predators.^[2] Paletta found greenbird wrasses and Niger triggers failed; bumblebee snails helped in small tanks or small areas but would take hundreds in a 500 gallon system.^[1] Mithrax crabs, hermits and several wrasses have given mixed results.^[2]

Prevention

Inspect new rock and coral plugs and remove vermetids before they go in.^[1]

How it spreads

They grow quickly and reproduce faster, and survivors anywhere in the system repopulate it.^[1]

Troubleshooting

Common mistakes

• •Buying a predator to fix them.^{[2, 1]}
• •Stopping treatment as soon as you stop seeing them.^[1]
• •Not inspecting coral plugs.^[1]
• •Relying on superglue alone.^[1]

Vermetid snails FAQ

Are vermetid snails bad?

Yes for corals: their nets irritate corals they touch, and in experiments one species cut coral growth by more than half and survival by up to 40 %.^{[1, 3]}

What eats vermetid snails?

Nothing reliably: Reefs.com says there are no proven predators, and wrasses and triggers failed for Paletta.^{[2, 1]}

How do I kill vermetids?

Cut tubes at the base, seal openings, take rock out and acid-treat the holes, or starve them with calcium carbonate dosed onto their nets.^{[1, 2]}

Are vermetids worms or snails?

Snails: stationary gastropods with shells cemented to rock.^[2]

Where do vermetids come from?

Live rock and coral plugs, especially maricultured coral mounts.^[1]