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Pond Snails in Your Pond

By: Dr Gareth Evans - Updated: 24 Mar 2017 | comments*Discuss
 
Scavengers Algae Detritus Radula Plant

Few issues divide the ranks of pond-keepers quite so readily as the topic of pond snails. To some they are nothing more than an aquatic version of an all too familiar garden pest, ready to wreak havoc on prized water plants; to others they are a fascinating and welcome addition to the pond, performing a useful job by helping to keep it clean. The truth is probably somewhere in between and one thing is certain – love them or loathe them – if you have a pond, you’re not likely to avoid them for long!

For and Against

Most of the common species of snails in British ponds are scavengers, feeding on plant material and detritus, scraping away at their food with a muscular, rasp-like tongue called their radula. In the days before the widespread use of UV clarifiers, this used to make them very popular with pond-keepers since their natural menu included prodigious quantities of algae. However since technology took over their role, fewer pond-keepers are prepared to turn a blind eye to their tendency to munch on water lilies and other specimen plants.

Snail fans point to their continuing usefulness in helping reduce the build up of decaying organic matter on the pond bottom. On the other hand, set against that is the contribution their waste makes to increasing nitrate levels in the water and the fact that they can act as intermediate hosts for a range of parasites – neither of which endear them to fish-keepers.

In the end, for most people, you either like them or you don’t – and that’s an end to it!

A Little Natural History

There are more than 30 kinds of freshwater snail in Britain, ranging from the likes of the tiny Dwarf Pond Snail (Lymnaea truncatula) to giants such as the Great Pond Snail (Lymnaea stagnalis) or Great Ramshorn (Planorbarius corneus). Although some snail-lovers will buy snails from aquarists suppliers or beg a few from friends’ ponds, freshwater snails have a habit of turning up, invited or not, usually attached as eggs on water plants. The eggs themselves are usually quite easy to see if you look for them, contained in a mound or strip of thick, jelly-like material on the surface of leaves and stems. Since snails are prolific breeders, once they are established in a pond, their numbers can increase very rapidly – so if you don’t want them, it pays to be vigilant.

There are two main groups of pond snails – the “pulmonates”, which breathe air using lungs and the “operculates” which get their oxygen from the water, using gills. Many of the species which are most familiar to water gardeners, including the Great Pond Snail and the various varieties of Ramshorns are pulmonates. The ability to breathe air gives them an advantage over their gilled relatives because they can colonise most types of pond, even when the dissolved oxygen level is low. By contrast, the operculates – snails such as Jenkin’s Spire Shell ( Potamopyrgus antipodarum) and Bithynia tentaculata are restricted to clean, well-oxygenated water.

The Sex Lives of Snails

Another interesting difference between pulmonates and operculates lies in their approach to reproduction. While most of the gill-breathing operculates have separate males and females, pulmonates are hermaphrodite, each individual being able to both fertilise and be fertilised by another snail – which goes some way to explain their ability to multiply quite so quickly.

However, the pulmonates aren’t the only ones with a clever breeding trick; Jenkin’s Spire Shell – an operculate – goes in for a spot of virgin-birth. Technically known as “parthenogenesis”, this allows the snail to reproduce without the need for a mate, which is a useful thing to be able to do if she find herself all alone in a suitable pond – although confusingly all of her “daughters” will actually be her sisters!

No matter how you feel about these animals themselves, it is impossible to deny that they are really very good at what they do. Even if they are never going to be your favourite kind of pond-life, their unique biology and remarkable ability to find their way to just about everywhere makes them an interesting group – however grudgingly you choose to admit it!

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Is it OK to introduce ramshorn snails to my small outdoor pond now? Or is it too cold?I have had them before but all disappeared over winter and big build up of algae on sides of pond. thank you Sylvia
Sylvia - 24-Mar-17 @ 9:30 AM
Please can you help, I found lots of emopty shells from my pond snails, lymnea stagnalis Why did they die?, my pond is small and abouy 18 inch deep, is it because it is too hot? I made sure that there is lots of plants around for a shade. Could it be some virus brought by birds on their wings while bathing? If they died of hunger what should I feed them with? I have also flatworms, would they be carrying some parasite? I do not have fish, and also there is no sign of frogs or frogspawn.... I covered my pond with plastic net to prevent birds from bathing they have separate bowl, because I am worried that this is the cause of my pond snails to die. Do not want to order any more snails untilmI know what happened. Please answer my Qs.
Anita - 23-Apr-16 @ 5:49 PM
have a serious problem with blanket weed have tried most remedies but it keeps returning its only a wildlife pond newts frogs dragonfly nymph etc no fish so im considering snails as the last resort any thoughts
ironside - 6-Jul-15 @ 10:52 AM
I have three ponds in my suburban garden. I have recently noticed that the common pond snail population has dropped a lot in two ponds, winter 2014, completely gone in the other pond strangely the red ramshorn snails are abundant. These ponds are left to evolve as they will frogs and toads use all three,no fish. Any idea as to why this has happened?
chorisia - 27-Mar-15 @ 5:59 PM
We have a large natural garden pond (approx. 15.5 m x 22 m) which is protected because we have a thriving colony of Great Crested newts, as well as Smooth newts. Over the years we have had the odd problem of blanket weed, but it is particularly bad this year. It started to grow vigorously when the pond was frozen over for a few days and the sun shone creating a greenhouse effect for the weed. We have plenty of the ubiquitous Great Pond snail (Lymnaea stagnalis), but no Ramshorn snails which I believe will feed on blanket weed. Could you please advise me if all the Planorbis species are equally efficient in solving our problem, or has one species advantages over the others. So far I have only seen Planorbarius corneus for sale. I should be grateful for your advice.
Neuseline - 24-Mar-15 @ 10:40 PM
Something has reduced my best pond plants to bare stalks.Are pond snails to blame?If so is there a way to get rid of then other than picking them out by hand? Brian Beckett
Brian - 19-Jun-14 @ 7:43 PM
Question: Can snails be used as a tool to control oxygen weed in rfesh water ponds?
dave - 24-Nov-13 @ 1:32 AM
Hey, I want to collect some Great Pond Snails from my local park (I have asked permission) but I want to make sure they are free of disease and pest. They are being put in their own "aquarium" set up, but I don't want anything getting in which will cause havocc. Could you please inform me of ways to ensure they are disease and pest free. Are there any parasites that could be spread to humans? How can I ensure they are clean? Thank you!
Arrex - 29-Jul-13 @ 10:53 PM
The best solution to keeping Herons out of ponds is to buy Netfloats which are brilliant.You just join them together in the shape of your pond. Bought off the internet. George
Cookie - 16-Jul-13 @ 6:48 PM
sounds like your snails are being eaten by something, perhaps the fish or possibly rats
phil - 26-Jun-13 @ 7:33 PM
I have three ponds.The two smaller ones that are crystal clear and packed with snails, weed, fish and other wild life.I use these ponds to supply snails to the large pond 11' x 14' x 4' deep.This pond however becomes a pea soup in the summer despite a good coverage of weed, lilies and edge plants.It is exposed to sun the whole day. Snails in this pond seem to die very fast.I am left with empty light coloured shells not crushed, so I don't think they are being eaten.Why is this happening and what can I do about it?I used to buy flea cultures to clear the algae, but the fish are now so numerous they don't stand a chance. Two more questions.How often do snails have to breath and how do they service the winter under ice?Do they hibernate? I hope you can help, it's hard to get all the information you would like. many thanks
Tamsie - 23-Jun-13 @ 10:33 AM
Like many of the other coments I have lost all my snails since last winter. I think they were doing a good job in keeping down the algae and blanket weed since this year bothhave increased greatly. There has been repeated visits by a heron and I did use a weed killer(Round up) around my ponds in early spring. Did any of these factors cause their demise? The fish seem OK only very nervous due to the heron. I am keen to reintroduce snails to my pond.
Erdy - 18-Oct-12 @ 10:42 AM
My ponds is full of snails! They have flourished in my pond but it is becoming a soup of snails. What should I do? Anyone want a few hundred?
Loz - 14-Sep-12 @ 11:55 AM
I am having the exact same problem as Jennifer with snails.A couple of days after adding the snails I have the clearest water ever.But after a couple of weeks as the weather began getting sooooo hot the algae has become out of control again and I cannot seem to find any of the snails. Any thoughts or ideas, or are they at the bottom mating or something and will return to do their jobs soon?
Chad - 7-Aug-12 @ 8:00 PM
Have pond depth 4 feet to 4 inches. Well stocked with plants. Some goldfish, frogs, toads, and newts. All my snails have vanished although the water has now warmed up. Noticed because of accumulating algae on pond walls. Any ideas anyone?
Jennifer - 7-Jun-12 @ 2:37 PM
Hi there, i wonder if you can help me ? Over the past week or so all the snails in one of my ponds have died. They have all changed colour from black to light brown. Other pond life appear unaffected. Any suggestions what the problem is ? Cheers.
hetchins - 2-Jun-12 @ 3:21 PM
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