Pests in the Garden Pond
The largest pest is usually the heron, a fishing bird with a decidedly fine taste for garden pond fishes; it arrives just after dawn and clears a pond of prize fishes before the owner is awake. Some keepers cover their pond with a fine net, placed well above the surface to prevent the bird’s beak from going through the mesh and spearing the fishes. Whether it is the difficulty of reaching a fish and swallowing it through the net, or the fearthat the bird is going to be caught in the mesh, is not really known, but most pond owners find this method effective. Another and less unsightly remedy is to restrict the bird’s flight path; poles placed close together will prevent the wings from spreading, and encourage the bird to look for an easier and safer meal. Black thread stretched over the pond and its surround can achieve a similar effect without spoiling the look of the pond.
Cats too are attracted to the movement and flavour of garden fishes. They can be prevented by netting, or by a pet dog. A quick shower of cold water from a garden hose is a harmless deterrent.
Most of the insect life found in ponds is in some way harmful to plants or fishes, but this is part of nature and provided the damage is minimal the whole cycle of life will continue. But where there is some imbalance, and one insect becomes too numerous, then remedial action is necessary.
Several types of beetles and their larvae can be considered pests in the garden pond. One to look out for is the Great Diving Beetle, Dytiscis marginalis. It is hard to miss this rapacious predator; the adult may grow to a length of 4cm (1.6in), its dark brown oval body sometimes margined in yellow. Using its powerful mandibles, this beetle will rapidly and with the utmost of selfless ferocity attack fishes larger than itself. The larva, up to 5cm (2in) in length, is even more voracious.
Among the harmful water bugs that are able to fly from pond to pond are the so-called Water Boatmen or Backswimmers, Notonectas, easily recognizable by their upside-down swimming action just beneath the water’s surface. Notonecta glauca, up to 1.5cm (0.6in) long, is the most commonly seen species. The Water Scorpion, Nepacinerea, also attacks fishes and tadpoles. Up to 3cm (1.2in) long, this water bug has a terminal tube that it uses for breathing and is easily mistaken for a scorpion-like sting. All these water bugs and beetles are difficult to eliminate.
In many cases, it is the larval stages that pose the strongest threat to pond fishes. This is certainly true of Dragonflies, for their larvae (nymphs) lie low in submerged burrows and pounce on pond creatures that venture too close. They will attack fishes up to their own length – about 5cm (2in) – and are difficult to eradicate.
Among those parasites that can be accidentally introduced with fishes or plants are the leeches. These worm-like animals are common in fresh water and grip theirvictims by means of suckers at each end of the body. They suck blood and may leave wounds that weaken the fishes and make them susceptible to other infections. Several treatments for these parasites are now commonly available. Many of them, however, are specific to single forms of pond life.
Fish lice, anchor worm and flukes
Fish lice (Argulussp.) and anchor worms (Lemaea cyprinacea) are both parasitic crustaceans that grip onto or burrow into the fish’s skin. The disc-shaped fish louse reaches up to 8mm (0.3in) in diameter and has two large gripping suckers. The anchor worm, up to 2cm (0.8in) long, penetrates the body tissue by means of jagged anchor-like appendages and can cause considerable wounds.
Both these parasites may cause affected fish to swim rapidly around the pond. Similar’distress symptoms’ are also seen in fishes carrying gill flukes (Dactylogyrussp). These are flatworm parasites up to 0.8mm (0.03in) long that attach themselves to the gill membranes. Skin flukes (Gyrodactylus) may also cause problems. Use an anti-parasite remedy for both these flukes.
This is caused by the sucking worm Neodiplostomum cuticola. In this case it is the larval stage that produces the symptoms – brown or black spots on the body or fins. Each spot is an encysted larva. This parasite may be introduced by snails or visiting birds, and is best treated with an anti-parasite remedy.
, particularly water , can become infested with aphids and other small insects. If your pond is well stocked with fishes, just push the leaves under the water and rest a piece of wood over them to keep the leaves immersed. The fishes will eat the pests, and the leaves can then be released.