Apart from the livestock deliberately introduced into the water, otherforms creep in uninvited, but most of these are beneficial, either keeping the pond clean or providing a ready meal for the fishes. Others are more trouble, however, causing damage to fish and plant life, especially the small fry and the young fresh growth; it is important to keep an eye on the health of the pond life and spot any damage to fishes or plants that may have been caused by an unwanted guest. Among the vast amount of livestock it is quite difficult to determine which is friend and which is foe, and it is impossible to keep an outdoor pond free from the visitations of insects and other life forms.
One of the few animals that needs to be introduced into the pond is the snail. There are a number of aquatic snails that will happily feed on debris and help to keep the pond clean without feeding on the plant life.
Planorbis corneus (the Ramshorn Snail) can be put into the pool to clean up unwanted rubbish. It is easily recognized by its handsome flat coiled shell, and breeds well. It will not damage useful vegetation, and is readily available from aquatic dealers.
Viviparus viviparus (the Freshwater Winkle) delights in feeding on dead and decaying vegetation, and is popular with f ishkeepers. If disturbed it will cling very tightly to whatever it is attached to, resisting any attempt to pull it off, no matter how hard.
Viviparus fasciatus is very similar to V. viviparus, and also eats decaying plant life; but it is also completely different, in that it releases itself the moment it is touched.
Most of the other snails that are found in the pond introduce themselves and can be left to populate the water unless they are seen to feed on your prize. Some are small and insignificant, others are larger. Some of the bigger snails are from the
Lymnaea family, which includes the Great Pond Snail (Lymnaea stagnalis), a snail that through indiscriminate feeding can cause a lot of damage and should be removed.
Amphibians visit the pond to lay their eggs or spawn; some fishkeepers find the spawn unsightly and remove it, but the young are beneficial to the balance of life in the water. Young tadpoles are excellent scavengers, starting off by eatingand progressing to animal foods. Frogs, toads and newts should all be welcome because they do so much good in the garden, removing unwanted pests such as insects.
Beetles and other insects
There are well over 200 different species of aquatic beetle; some of these are savage and carnivorous, attacking fish and other water animals, but most are happy scavenging among the debris and keeping the pond clean. Unless attacks are seen, it is best to leave most beetles alone.
Surface walkers are often seen traversing the water relying on the surface tension to stop themselves sinking. The best-known of these is Gerrisnajas (the Pond Skater), which literally walks across the water on the lookout for dead or dying insects.
There are a large number of flies that leave their eggs in or close to water, from the humble midges and gnats to the larger caddis flies and dragonflies. Their eggs turn into larvae that prey on lower water creatures, other larvae and tiny fishes, and they in turn become food for larger fishes. There are over 160 different kinds of caddis fly. One of the commonest is Phryganea grandis with pale grey-brown wings and yellow-ringed antennae; it folds its wings along its body when at rest, like all the caddis flies. Their larvae form cases or tubes from fine particles of vegetation, stones, sand or shell to live in until the next stage in their development into flying insects.
The dragonflies form a large group of insects well-known for their spectacular colouring and erratic flight pattern. Their eggs are laid on the water surface and then sink to the bottom. When the larvae are hatched they form burrows in which they lie low, preying on small aquatic animal life; then they gradually change until they eventually become flying insects. Dragonfly larvae (nymphs) can be considered a pest. Among the other flies are Culexpipiens (the Common Gnat) and Chaoborussp. (the Midge). The larvae of these are a good food for fishes, and anyone who fails to keep fishes in the garden pond is likely to become aware of a subsequent noticeable increase in the gnat and midge population.
Other Freshwater Creatures
Among the other forms of water life is Argyroneta aquatica (the Water Spider), which manages to live and nest under water without drowning, due to the air secreted between the hairs on its body; it feeds on land and aquatic animals. Aquatic worms such as Tubifexare very similar to the common earthworm, but of a transparent red colour; they provide a useful source of food for the rest of the pond’s carnivorous animals.
Among the crustaceans that live in fresh water is Gammarussp, (the Freshwater Shrimp), which is a good scavenger and provides food for fishes, particularly trout. Asellussp, (the Water Louse) is another scavenger, and lives on decaying vegetable matter.