Control of Nemerteans in Vivaria

What the heck's a nemertean?

The phylum Nemertina (or Nemertea, occasionally Nemertini) contains the ribbon worms or proboscis worms, a group of about 1200 species. Nemertine worms are unsegmented and distinguished by possession of an evertible proboscis that, in many species, is armed with a poisonous stylet used in the capture of prey. Ribbon worms are carnivorous, feeding mostly on small invertebrates. Most Nemertea live in shallow seas and coastal waters, with a few inhabiting freshwater or damp soil. They range in length from 1 mm to as much as 60 metres.

The ones commonly seen in vivaria are 1-4 cm long and vary in colour from white through yellow and red to dark brown. They have a characteristic pointed end ("snoot worms") which moves in a distinctive way, sweeping around for prey items. In high humidity, e.g. after spraying, they swarm up the glass.

Where do they come from?

Who knows? Presumably they come in with tank furnishings, plants or field sweepings, etc. However, once you've got them, they do tend to spread from one vivarium to another, possibly on your hands but probably with plant cuttings or unsterilized tank furnishings.

Do they do any harm?

After years with these things in my vivs, I've got no evidence that they harm frogs or eggs.

So why do you want to get rid of them?

Two reasons.
OK, I'm a tidy freak. I just hate the sight of them crawling up the glass. I can't walk past a viv without removing any that I see, which takes a lot of time. They're an itch I have to scratch.
Better reason: they are predatory and eat springtails, flies and pinhead crickets. It's impossible to maintain springtail populations in vivs with these worms, which is a shame.

How do you get rid of them?

1. Complete teardown, throw all the plants away and sterilize everything else. The problem with this is that if you have them in multiple vivs, they tend to spread, and will probably just come back in time, so unless you're prepared to tear down all your vivs and start completely from scratch (with no guarantee that you won't get reinfested the same way you did originally), this approach is a non-starter.

2. They need moisture, so don't do well in dry environments, but that's not much help if you're keeping dendrobatids.

3. I have not found any chemical which can eradicate them without harming frogs and/or plants.

4. Biological control. A long time ago, someone suggested to me that nematodes sold for garden pest control could be used to eliminate them. Originally I planned to set up test vivs deliberately infested with nemerteans to try this, but it occurred to me that I also needed to know if the nematodes were harmful to frogs, so I summoned up the courage to try an experiment on a few vivaria.
I bought Phasmarhabditis hermaphrodita ("Slugsure") and Steinernema kraussei ("Grubsure") nematodes preparations from www.defenders.co.uk. These are produced and distributed by www.beckerunderwood.com and are available from suppliers in various countries.
The microscopic worms are supplied in a clay carrier and the preparations are designed to treat a designated number of square metres of soil. For this reason, it was difficult to follow the exact dosage, so I made up a thick suspension of the preparation and watered it onto the vivaria from a watering can with fine rose.

The good news: No harm came to the frogs, so the nematodes appear to be harmless.

The bad news: No harm came to the Nemerteans either - I saw no reduction in their numbers after the treatment, suggesting that the nematodes are quite species-specific.

I'm still hopeful that some biological control will be found to control these pests, possibly a coleopteran of some sort, although this will probably require the frogs to be removed while the treatment is taking place, either to protect the beetles from predation, or the frogs from possible harm.

If you find out how to control these things in vivaria, please let me know!

Update:

I have recently had a limited degree of success in reducing the Nemertean populations in contaminated vivaria by adding the woodlouse Oniscus asellus to the vivarium at the rate of approximately one per five litres of vivarium space. This reduces but does not eliminate the Nemerteans, presumably because the woodlice consume the eggs or young worms. The effect wanes with time as Oniscus asellus does not seem to like wet vivaria and any offspring produced are consumed by frogs or Nemerteans, so the population is not sustained at the necessary level for control.
Oh well, it's a start.

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