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Leeches In My Pond!!!


I pulled out a solar powered water pump out of one of my ponds to clean the filter and found quite a few small leeches crawling about the casing. Perhaps those of you who have well established garden ponds have found that they have become residents in yours too. #@$&&-*$:0 I cried out! You see, a few years ago I lost about 60 fish in my ponds all beautiful fantails to a mink, not one left alive. Now was I about to go through the same thing with a slimy parasite?
My first question was how were they introduced to my pond. The answer to that was either the eggs or the leeches themselves came from snails, plants and or the fish themselves which I purchased for pond restocking purposes. Curious thing though, after netting many pond fish, snails, frogs and pollywogs I found no attached leeches. Ok what is going on here? So to answer that question I commenced to educate myself about them.
What I have learned is that there are two types of leeches which can inhabit a garden pond. First, the classic bloodsucker parasite one which was applied to those suffering from “dropsy” aka congestive heart failure to introduce its anticoagulants into the hosts blood stream to prevent life threatening blood clots from developing in circulation slowed by fluid swollen limbs. The second type of leech was one which resides in the muck and debris at the bottom of a pond feeding on that substrate. In order to find out which type I have my readings suggest that I make a leech trap. This trap is made out of a metal coffee can with small holes punched through the sides with a nail. Then a few rocks are placed in the bottom to help it sink to the bottom of the pond and then inside the coffee can it placed the bait which could be a few pieces of liver or kidney. The lid is then popped on and the tethered can is lowered into the pond. The cans contents is then checked a day later and a leech census is made. If very few or no leeches are found inside then the blood sucking parasitic type poses no problem, in fact, the can trap most likely cleared the pond of those leeches. Nothing in the trap would indicate that those leeches in the pond are the non parasitic debris eating type which are a good food source for the fish. So in the next few days I will find out what kind of leeches my ponds have using this simple method. Perhaps those GOYers with ponds might try this too.

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Oh dear. Thats the one member of the animal kingdom I cannot abide at any price. If you are going to investigate yours its good to hear you aren't as squeamish as me about them.

14 Jul, 2018


How interesting! Fascinating what wild life throws at us! Let us know which type of leech you got after your experiment. I have been plagued by maggots in my recycling caddy as my teenage sons never close the lid on it properly! Really can’t stand them and have threatened to leave some in my sons beds next time I come across them! Lol

15 Jul, 2018


They are closely related to earthworms from what I understand.

15 Jul, 2018


That is very interesting. We have a large pond/small lake in Sweden and I often wonder if there are any leeches in it. This is a good way to find out.

15 Jul, 2018


I have sent your blog to my son in Sweden.

15 Jul, 2018


This is useful info about the different types of British freshwater leeches, I believe there are about 50 types in the US:

I once found 5 or 6 fat black ones all curled up under stones in my bog garden (hibernating apparently). Freaked me out as they were about 6 ins long when stretched out - like this one:

18 Jul, 2018


Well, my leech collecting will be delayed a bit. I have developed Bell’s palsy-a paralysis of the facial nerve, right side in my case. As soon as I realized that I could not blink my right eye or make a full smile, I evaluated myself for stroke (the Cincinnati prehospital stroke scale). That being negative I went right to the hospital to start taking a heavy regimen of prednisone and took a blood draw to test for Lyme disease from a tick bite. The Lyme test was negative so the cause of my palsy was not gardening related. Luckily, my early intervention resulted in minimal facial disfigurement and I hope to get back most muscle function in the coming months.

22 Jul, 2018


Oh dear, Mike, I am so sorry to hear that. I looked it up as didn't know exactly what it was but I was pleased when I read it is a temporary condition, that at least is a mercy.
Do take care of yourself & keep taking the tablets. Hope recovery is quick for you.

23 Jul, 2018


We also have small leeches in our pond as well as the planarians you have subsequently found. They can also enter the pond when a bird drinks from the water and the leech hitches a ride in its nostrils. waterfowl often have them as hitchhikers. The good thing was the ones I have are not the fish leech Piscicola Geometra.
I once found a horse leech [Haemopis sanguisuga] under a stone in the garden. that was a huge one but a beautiful colour.

glad you are feeling better, Bell's palsy isn't that pleasant is it.

11 Aug, 2018


I know that birds were a vector for many forms of pond pond life, feet and feathers yes but I had never considered the nostrils. Thank you for that info. The cause of Bells Palsy as now being considered as a viral infection though much is still unknown as to type of virus and method of transmission although a little over a month ago one of the members of my skeet shooting club was afflicted by this same malady.

11 Aug, 2018


GF thank you very much for the UK “Know Your Leech Guide”. As of this time it appears that I have made a good recovery and I go back to the ophthalmologist in a few weeks to have my eyesight and eyelid function re-evaluated.

11 Aug, 2018


Thinking of you, Mike & fingers crossed for your evaluation & full recovery.

11 Aug, 2018


Glad I have found this site though the leech conversation is almost three years old now I see. Is there anybody out there who is still interested?
I have a very small garden pond inhabited by freshwater snails, purchased specifically with the idea of cleaning up the surplus algae. The water is now crystal clear.
I fancied getting a few small freshwater fish to add interest so purchased three goldfish. By the next morning they were all dead, suffocated by a profusion of what I assume were leeches, all over them, brown wormy looking things, 10-12mm long which contract to 3-4mm when disturbed.
The snails are flourishing, by the way. I float lettuce lettuce leaves on top of the pond as a treat for the snails and I find that my "leeches" (if that is what they are) attach themselves to the underside of the lettuce leaves by the dozen, from whence they are removed and dispatched.
Interested in the coffee can idea though such cans are hard to come by and I may need to improvise so I’ll let you know how things evolve.
I would prefer goldfish to leeches, and while I have nothing against leeches as such, it looks as if the two cannot live happily together so the leeches are going to have to go.


15 May, 2021


Hi SuffolkTony: The leaches in your pond aside from the vectors mentioned in my blog could have hitched a ride on the snails you introduced into the pond. It seems that the fish dying in less than a 24 hour period could have suffocated from a lack oxygen only. You mentioned that you have a small garden pond so one small goldfish would be the maximum. Also, to keep fish, you must have well aerated water. This is accomplished by an aerator with bubble stone and or a pond water pump with a waterfall type feature that will establish a well oxygenated water current in the pond. If you don’t have these oxygenation methods or are not capable of having them due to a remote local for an outdoor electrical then the fish will not survive a static garden pond. Oxygenation via water plants is sometimes suggested, that method is a classic fail since the oxygen generation is not at an acceptable rate and ends when the sun goes down. So I would suggest that to add interest you might consider placing an inexpensive solar powered water feature in the pond such as a floating solar powered fountain which can be found and purchased on the web. You can also purchase some small flowering pond plants too which can add interest. I might add that the objective to establish crystal clear water in a garden pond is an epic mistake since algae provides biodiversity in a pond. If you have string algae, remove it by twirling it around a bottle brush and lifting it out. As far as the floating algae that gives the water a pea soup appearance the introduction of pond plants will take care of that. Welcome to GOY!

16 May, 2021


Dear Loosestrife2,
Thank you for responding and for your useful suggestions, all of which are noted.
When I fished the corpses out of the pond I was dismayed to see just how many leeches were attached to each fish and, very disappointingly, the leeches were completely blinking the gill openings. The fish certainly suffocated but doubtless aided by the leech load.
I am embarrassed to say that I had not noticed the size of the leech population beforehand. We have a thriving crop of oxygenation plants which I removed from the pond and rinsed them in a bucket of water. There were, literally, many hundreds, running into thousands of leeches I fear. Now dispatched, of course, and in addition I set up a leech trap with an empty yogurt pot with a clear lid. A hundred or so more captives overnight and as many today by the look of it.
I had been investigating an oxygenating pump, solar powered, and then went outside and found the dead fish, but I won’t be getting another fish (the 3 I bought were pretty small, no bigger than 2.5" long), fountain or no fountain until I have got the wildlife under control. If you are right and they hitched a lift on a snail they are breeding like there’s no tomorrow so I might be fighting a losing battle.
We had already got half a dozen nice pond plants so the whole set up is starting to look attractive and interesting, albeit small.
Maybe I’ll concentrate on snails, they seem at home and are interesting, in a rather slow and sedate kind of way.
Thanks again.

16 May, 2021


I have been thinking about this a great deal and I’m afraid I may have been looking at things incorrectly. My first impression that the leeches overwhelmed the fish was probably wrong and the fish died of a lack of oxygen in the water. The leeches were then attracted to the dead fish.

Do you agree?

Presumably, given well-oxygenated water, fish and leeches can co-exist. I still have too many leeches for my liking but if I concentrate on getting the water better oxygenated with a pump, in addition to oxygenating plants, would you think that I can try to introduce small fish again in due course?

I am reluctant to give up so any advice greatly appreciated.


17 May, 2021


You are now spot-on Suffolktony! May I suggest to you a smaller fish that will remain small and do well in an outdoor environment such as Gambusia aka Mosquito fish. Goldfish though purchased small will not remain small thereby increasing the oxygen demand. If goldfish, then purchase no more than two. They like company. I live in the USA so I don’t know how available Gambusia are in the UK but if you can get them 5 to 8 would be alright. With pond pumps you will find that you will have to clean the string algae off them once a week so get a pump that can easily be accessed and the strainer cleaned. If run by house current make sure you have Ground Fault Protection even though you will pull the plug any time you place your hands into the pond. Do not place any algicide into your pond for you will kill not only the string algae but the precious biofilm established in the pond. If done, the fast drop in oxygen dissolved in the water will kill any fish in a matter of hours. Do not make the mistake of having the goal of attaining pristine crystal clear water....that is for drinking glasses and definitely not for ponds. Keep in mind that in order to have a good ecosystem the unseen microbial life in your pond must be maintained too. Very Best Regards: LS

17 May, 2021


I agree that you need to oxygenate more and then the fish should be fine. 2-3" sized goldfish should be fine.
I seem to remember that they grow to 'fill' the space so to speak. In a small pond they stay small and then when/if they go in a bigger pond they will grow bigger. That certainly happened when we moved house.

17 May, 2021


Thank you both for the useful comments. The leech numbers are much reduced. I have discarded all the old oxygenating weed and will replace. Have also ordered an aerating pump so will give everything a while to settle down and then look to source some small fish.

19 May, 2021

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