Lymnaea stagnalis is widespread in the temperate zone of the northern hemisphere, from western Europe to China and further in North America. In our country it is a common species found in stagnant and also in gently flowing waters. It particularly prefers tanks with dense aquatic plant growth… and is often found in muddy places, which is not surprising given its name.
If you come across this snail in the wild, you usually won’t mistake it for anything else. It’s a large species, and its shell can reportedly be up to 7 cm in size. The individuals I collected in the Danube arms and then photographed at home in my aquarium measured around 5 cm.
The shell is relatively fragile, with coils elongated to the tip. There are about 5.5 to 7.5 threads, and the largest one is quite robust and wide compared to the others. Ulita is really very pointed and elongated, which distinguishes it from similar species (which do not grow to such dimensions).
A very striking feature of the rays are their antennae. They are flattened into a triangle, which makes them look like ears. Their large surface area – like the entire surface of the body – is used for breathing. They have “aquatic lungs”, so they often come to the surface to breathe, but in winter they spend most of their time in the lowest layers near the bottom, breathing through the surface.
The swimmer, like all lung-bearing gastropods, is a hermaphrodite. Normally mating occurs between two individuals, but it is not entirely rare for self-fertilization to occur. This is especially true if the floater finds itself in a previously uninhabited area. However, in mating – unlike the related snail – only one of the gastropods always acts as the male and fertilises the other, so the exchange of sperm is not mutual, although the roles may later be reversed. The reproductive capacity of gastropods is enormous, with a mature gastropod laying up to 300 eggs in a single clutch.
The eggs are almost always found on plants. They take about a week or two to develop. Then they hatch into miniature snails that grow very quickly. Two generations can be produced each year. A snail can live up to five years, in most cases much less, of course, and unfortunately it rarely lasts more than a year in the aquarium.
The short lifespan of the floatfish in the aquarium is due to the water temperature. Although this snail can tolerate the conditions of a normal aquarium, it will not live beyond eight months of age at a temperature of 28 °C. In the wild, it is active all year round, except during the most severe frosts.
If you are thinking of keeping rafts, you must take into account their appetite in addition to the temperature. I’ll keep it short – they eat a lot, and they eat plants too. Not like marisa, but you’ll feel it. However, they prefer algae of all kinds, which they process with a strong radula. They also destroy the dying leaves of plants. In addition, in a pinch, they will also eat animal food, they may eat smaller snails (lionfish, crustaceans) and of course their eggs.
On the other hand, in the case of juvenile floaters, there is a risk of being eaten by hungry fish and large gastropods (Pomacea or Marisa) because floaters do not have an operculum.
Lymnaea stagnalis is, as I have already written, a common species in our nature, but getting it among aquarists can sometimes be a problem. However, I strongly recommend thinking about quarantine if you get “wild” snails.
In the wild, much of the population can be hosted by flukes. The likelihood that you will bring home an uninvited guest along with the snail is close to certain – but it doesn’t always have to be a parasite, as just about anyone can live on a snail shell. Most of the time, even the fluke stages do not harm the snails, although they do reduce their fertility and, in the case of a severe infestation, certainly their overall vitality – in any case, you will not be able to tell anything by simply observing a newly introduced snail.
The final host of cercariae, the developmental stage of flukes, can be fish, amphibians, birds, mammals… Yes, most certainly fish, so don’t put snails from the wild in your aquarium with your frilled pets; and mammals, including humans. Some time ago I used to hang around a lot with botanists specialising in aquatic macrophytes – and believe me, some have had their own very unpleasant experiences with cercariae.
In addition to being parasite hosts, swimmers are of interest to science for other reasons. They’re used for toxicological studies. Their hormones are isolated and studied. Countless studies are being conducted on their enzymes, neurons, genetics – different parts of their bodies are being prepared, isolated, stained, irradiated. Scientists are looking at their rather simple nervous system and analysing their ability to use memory. Yes, these gastropods have long-term memory and can demonstrably learn. There is a great deal of variation between individual gastropods in their ability to remember after a single taste that something is simply not good. For example, pinnipeds can be taught not to run out of the aquarium, that there is something unpleasant waiting for them, etc.
If you provide them with good living conditions, they won’t run anywhere and you can have fun watching them ballet on the underside of the surface. Because of its size, you can see everything about this snail, its “facial expressions”, its eyes, its mouth… and it’s something to behold. If you like snails and don’t care too much about the appearance of your fine-leaved plants, I can only recommend this float.