The lush vegetation around the edges, the open water, the numerous submerged and floating weeds, and the muddy floor make ponds a haven for many insects. It is also an excellent place for amateur naturalists to find some exciting insects, provided they know where to look.
Insects can be found at every depth of your pond. Pond skaters and Water measurers can be seen skating around on the surface, while water beetles can be found in open water. Scraping the bottom of the pond will show a healthy amount of dragonfly nymphs.
Ponds are packed with insects, the various species occurring in many different zones around the water’s edge, among the submerged plants, in the open water, and on the muddy floor of the pond. The best ponds for finding insects have sloping sides and shallow edges with flourishing marginal vegetation.
Surface Dwelling Insects
Several species live on the pond’s surface, so just by sitting quietly and watching, you should be able to see some activity. The long-legged Pond skaters of the genus Gerris move jerkily around, picking up small insects, such as aphids, which have fallen or been blown onto the water.
The extremely thin Water measurer steps over the surface with long legs and body clear of the water. If you try to pick it up carefully, it may feign death. You may also see a group of small black whirligig beetles charging about on the surface quickly, never bumping into one another.
With a strainer, try and obtain a sample of the floating egg rafts of mosquitoes and their larvae and pupae from the water surface. The eggs float on the surface, but the larvae and pupae hang under the surface film, with gnat larva at an angle from the surface and the mosquito larva parallel to the surface.
Open Water Insects
The next area in which to look for insects is the open water. Dip your net in the water and draw it backward and forward four or five times, sweeping through submerged vegetation on which the swimmers may be resting. Make sure not to scrape the bottom of the pond.
Get a large dish with clear water, and put your catch in it. Active swimmers can be seen straight away, with large or small water beetles such as the Great diving beetle and Backswimmers of the genus Notonecta which, as their name implies, swim on their backs.
Some insects, such as Backswimmers, carry down a bubble of air that they use for breathing, coming up to the water’s surface to breathe in more air. They can be recognized by their silvery appearance on the undersurface.
The smaller, Lesser water boatmen Corixa are often very common in ponds. They can be seen swimming in pondweed, water crowfoot, and on the undersurface of such plants as water lilies.
The oval-greenish Saucer bug, a particularly good swimmer, is about 15mm (1in) long and has a strong piercing mouth, capable of giving the human thumb a sharp prick, so be careful if you try to handle these.
Insects On Submerged Plants
Several insects may appear if you fish some of the plant material out of the water and float it in a large bowl of clear water. Some will be true swimmers, while others are species that clamber about the plants after crawling up from the bottom of the pond in search of food.
One fascinating larva, quite common in ponds, is that of the Phantom midge fly. It is extremely difficult to see about 10mm long when fully grown since it is transparent. You can see it by its black eyes and two air sacs, one at each end, which help to balance it in water.
When a small animal like a water flea comes within reach, the phantom larva grabs it with its antennae, as it doesn’t have any legs.
Found among plants near the bottom of a pond, the conspicuous Water stick insect Ranatra linearis is a thin brown creature about 5mm (2in) long. Its front legs are much shorter than the middle and hind pairs and are used for grabbing prey.
A close relation is the more common water scorpion Nepa cinerea, a flattened brownish oval creature. Both have a long tail about one-third of their body length, which acts as a snorkel. This allows them to take in water without exposing themselves to the dangers of predators above the water’s surface.
Insects On The Pond Floor
The bottom of the pond, the home of crawlers and mud dwellers, can be scraped with a net to obtain the next set of specimens. In shallow water, a spoon can be used to bring up samples of mud or sand for examination in a pie dish.
Most ponds will have some dragonfly nymphs, especially those of darter flies. A particularly rewarding sight is when the nymph crawls out of the water and onto a stem, where it becomes transformed into a mature dragonfly. This happens in about an hour, so you can watch it and record it from start to finish.
Another interesting thing to watch is the nymph’s feeding habits. Its mouthparts can shoot out to grab prey, such as a worm or another dragonfly nymph. If the intended meal is not near enough to be grasped, the nymph propels itself forward by a sudden expulsion of water from its rear end.
This action is best seen by placing a small amount of mud or sand in the bottom of the bowl so you can see the jet of water.
A good sample of mud from the bottom of a pond can also contain some bright red, bloodworms, the larvae of Chironomus midges.
Their red color is due to the presence of hemoglobin, a substance that absorbs oxygen, helping the larvae to breathe in stagnant ponds.
Caddisfly larvae are well known for the homes that many of them constructed from pieces of plants, sand, or small stones. They creep about the pond bottom and inhabit better-aerated ponds. Phryganea, a genus with several common species, has larvae that build cases of the root, reed, or other pieces of plants in the form of a neat spiral cylinder.
Looking in your pond for insects is just the start of an amazing journey. The food web in a pond is complex and not easy to follow. Besides birds, fishes take a heavy toll on aquatic insects, but there is still much that isn’t known. By looking in your pond and finding what insects you have in there, you can then work out what might be feeding on them.