Too many snails?

A resident frog

The garden pond has been a source of much entertainment for me over the past year. One of the few advantages of being in too much pain to work is that I have been able to take the time to simply sit back and watch as nature has gone about its business. Our pond is only about 6 m² large and is not very deep, but there is so much going on. It has been simply teeming with life, from the alien-looking larvae and diving beetles to the much larger visiting frogs and dragonflies. Best of all has been watching the newts, from their first appearance in spring, through the frantic breeding season to their departure in early autumn.

Back in the spring the pond was in a sorry state. It was still full of creatures, but these were scarcely visible due to the suffocating swathes of blanket weed and duckweed clogging up the water. The pond was also choked by a proliferation of decaying leaves, deposited there by a nearby tree the previous autumn. Drastic action was required.

We decided that the best way to clean up the pond was to remove huge clumps of the leaves and weed by hand, sorting through the noxious-looking mess to ensure that no living things were discarded. Before long we had a whole menagerie of weird and wonderful creatures collected in a bucket: beetles, bugs, and boatmen mixed in with the occasional amphibian. It was tiring but fascinating work. When we were done the pond was by no means perfect, but looked significantly better. We returned the creatures to their home and waited for things to settle out.

One of the newts I found in the mess of leaves

The duckweed had been conquered and the bulk of the leaves removed, but things were still not right. Despite our best efforts, the blanket weed was still there. The problem with blanket weed is that it grows, and it grows fast, expanding at a quite frankly terrifying pace on hot days. It had to be removed, but how? Luckily, inspiration struck and I devised a cunning approach to this: using a broom to simply sweep out the weed. Its green fibrous tendrils stick readily to bristles, meaning that with just a few minutes work the pond could be made much clearer. However, if even the smallest bit was left this would expand rapidly and the next day the pond would need to be 'broomed' again.

We had discovered one good weapon, but we needed to open up another front on which to attack the masses of blanket weed. The broom was a mechanical approach, and so perhaps it was time to attempt something a little more biological. We headed off to the garden centre and returned proudly wielding a water-filled bag containing seven snails. We crossed our fingers and hoped that these would be hungry molluscs, eager to chomp down every last vestige of weed.

At first not a lot happened. The pond still required regular brooming, and we rarely clapped eyes on its newest inhabitants. But then, one day, the blanket weed was gone. The water was crystal clear; we could see everything. And everything included one hell of a lot of snails. They were everywhere, not a single patch had been left uncolonised. They came in all sizes, from the barely perceptible to those several centimetres long. It was a remarkable transformation.

It is of course good to be rid of the blanket weed, but we are now wondering if we have simply substituted one bane for another. Can such a huge number of snails be healthy? Will they naturally regulate their numbers in a sensible fashion, or will there be a population explosion followed by a mass death as the pond is drained of resources? Will their excrement make the pond too toxic for other creatures? Troubling questions indeed.

Friend or foe?

Deciding that no harm, and potentially some good, would be done by a little intervention, I decided to remove some of the snails. Just working from one corner I scooped out about fifty and put them in a bucket along with some weed and sediment for them to munch on. The places these had occupied were quickly filled by others, and when I returned a mere quarter of an hour later it was impossible to tell that I had taken any out.

And now I have a new dilemma. What do I do with a bucket full of snails? I could try to sell them back to the garden centre, thus making a huge profit, but I'm not sure they'd be accepted. I could try and fob them off on neighbours with ponds, but they probably have plenty of snails of their own. I can't put them in the river as we can't tell for certain what type of snails they are, and we don't want to risk harming the ecosystem there. I need a plan, and I need one fast as I doubt snails enjoy living in a bucket. Any ideas?