They came in with a portion of live blackworms I had ordered. My culture lasted about two years or so, until the leech population exploded in the culture and probably wiped the blackworms out (culture may or may not have crashed independently during that time).

I have no doubts that in such large numbers just like showed in the pictures, these can gang up on shrimps and snails and wipe them dry. However, I do wonder what kind of conditions might lead them to reach such large numbers. They’re at least present in all my tanks like I said, some of them are shrimp/snails only, some of them are quite overfed, but I’ve never had troubles with keeping snails or breeding shrimp.

They take a long time to mature and look like any other detritus worms as babies. Their longer life cycle probably explains why they seem overall not to be as harmful, as they are easier to keep in check. I rarely ever see a fully grown individual, especially in any tank that has vertebrates in it.

I’m thankful for the awareness that these may not be harmless as we might think, but just thought I’d chime in with my own experience of them. In my opinion, if one notices Asian leeches in a tank, one should not panic immediately. Unless the population gets to large numbers of adults, one might not need to eradicate them, and should just keep an eye out for them and pluck out adult sized individuals when possible. In fact, I wouldn’t be surprised if they can serve some useful niche in a tank’s food web in the right conditions. Perhaps outcompeting or predating on other parasites that may be more harmful, aererating substrate, serving as food for vertebrates, being efficient detritivores etc., while being relatively harmless as long as the adult population remains low.

From what I have heard snail leeches can be much more voracious and problematic, even in smaller numbers.

I have indeed noticed since then just how common they are and how often they are mistaken for planaria. Although, due to probably their much slower life cycle or other factors, it seems to me like Asian leeches might be (?) overall less undesirable. Shrimp only tanks are definitely the most at risk of them being a problem, especially if fed generously, perhaps?

P.S. These actually managed to out-compete my rhabdacoelas and saved the day! Snail babies are safe again 🙂 Thank you so much for all your help!

In reply to Jessica …. You are taking about thousands of species. Some will be killed by freezing, some won’t. Medications such as Fenbendazole won’t damage the body structures. And determining which will kill snails would seem to be impossible.

In reply to Brad … In general most species of pond leeches do not attack fish. The slime coat on the fish prevents them from attaching.

Do they harm(attach to) fish? White cloud mountain minnows

In reply to Tony …… No, salt will do nothing to leeches