Molluscs, Amphibians, Reptiles and Snails

There is a multitude of freshwater pond snails, but for the majority of pond owners, only one species is worth considering: the ramshorn snail (Planorbis corneus), which has a flattened shell that is carried upright on its back. For the indoor pool or aquarium, there are both red and white-bodied forms, but a black form is produced in large quantities for the pool owner. All three are hardy. If introduced with either the red or white variant, the black form would provide the dominant colour.

Ramshorn snails are extremely useful additions to the pool, feeding almost exclusively on algae, especially the tiresome, filamentous mermaid’s hair, which so often coats planting baskets and the walls of the pool. In the balanced pool, they reproduce quite freely, producing flat pads of jelly containing several dozen eggs, which they stick beneath the floating foliage of waterlilies and other deep-water aquatics. If there is an over-population of fish, many of these eggs will be eaten; likewise, adult snails may be devoured.

Sometimes, the freshwater whelk (Limnaea stagnalis) is sold as a pond snail. While it will graze on algae, it much prefers the floating foliage of waterlilies. In most pools, it is undesirable, creating more damage than benefit. In the wildlife pool, however, a few may be considered acceptable. A distinctive species, it has a tall, spiralled and pointed shell and a fleshy, greyish-cream body. It lays its eggs in a similar fashion to the ramshorn snail, but in long cylinders of jelly.

 

MUSSELS

Two species of freshwater mussel are considered useful additions to the garden pool: the swan mussel (Anodonta cygnea) and the painters’ mussel (Unio pictorum). The former has a dull brownish-green shell, which is roughly oval in shape-and contains a white fleshy body. It may grow as much as 10cm (4in) long. The painters’ mussel is usually smaller and has a yellowish-green shell, marked with distinctive, dark brown growth rings. This may be introduced into a pool along with little fish called bitterling, the mantle cavity of the mussel being a refuge for the eggs and an essential part of the breeding cycle. However, this is very much the province of the fish keeper, rather than the water gardener.

The importance of the swan mussel to the ecology of the pool comes from its ability to remove suspended, single-celled algae from the water by sucking in green water and discharging clear. This will not make a significant difference to a very green pond, but the addition of a number of specimens to a well ordered water garden will be beneficial. It is not wise to introduce mussels to a new pool; they need a quantity of detritus on the bottom in which to settle down to a useful life. A new and relatively sterile environment is anathema to them.

 

FROGS, TOADS AND NEWTS

Whether you have the opportunity of introducing them or not, it is quite likely that these amphibians will eventually find their way to your water garden. Some fish keepers express concern over the introduction or presence of frogs in a pool, claiming that male frogs will occasionally attach themselves to fish during their mating period, clasping them around the head and gills, causing damage. In reality, however, this is likely to be a rare occurrence, and it is almost unknown if a suitable female frog is available. The common frog (Rana temporia) is the species that is most likely to arrive unannounced, although the edible frog (Rana esculenta) may also appear. Both are a muddy green colour and the edible frog has a distinctive pale stripe down its back.

Toads live a similar life to frogs, but are mainly nocturnal and often spend longer periods out of water. The number of species to be found is extensive, but for most pool owners, the common toad (Bufo bufo), is a favourite and almost certain to turn up. A dull olive or brownish creature with a somewhat warty skin, the common toad should be cherished, for it is the gardeners’ friend, being a regular predator of slugs, snails and other pests. The natterjack toad (Bufo calamita) is also a friend, and a handsome one, having a distinctive yellowish or orange stripe down its hack.

Newts are probably not as appreciated as frogs and toads, but they do make a valuable contribution to the life of the pool. The species most likely to be encountered are the common newt (Triturus vulgaris) and the tiny palmate newt (Triturus helveticus). Both are a similar brownish or olive colour, the males of each species having wavy crests and orange bellies.

 

REPTILES

Among the reptiles, the European pond tortoise (Emys orbicularis) is the most fun. Although it will eat small fish, it is a delightful character that will enjoy sunbathing on the edge of the pool. It may have a black or deep brown carapace with yellow spots and a black body, which is also freely marked with yellow. The closely related American pond tortoise ( Emys blandingii) is also good value, although generally of much duller appearance.

The Spanish terrapin (Clemmys leprosa) is an altogether different creature, being much less outgoing and quite reserved until familiar with its owner. Its shell, or carapace, can vary in colour from light olive-green to almost black, while the legs and head will be variations of these colours, liberally marked with yellow stripes. The Caspian terrapin (Clemmys caspica) is slightly smaller and has grey skin, delicately marked with a tracery of yellow lines, while the Reeves terrapin (Geoclemys reevesii) is of similar size, but has a dull brown shell and yellowish underside.