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Aquatic Life

Updated Wednesday 9th November 2005

Robert Saunders takes a dip into the rich variety of life in and around water

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Giant mayflies Copyrighted image Icon Copyright: BBC

Insects are probably the most successful of animals. It should come as no surprise therefore that they have been very successful in colonising the fresh water environment.

There are both advantages and disadvantages in living in the water: for example, the water can be a good means of dispersal for new generations, but all animals have to overcome the fundamental difficulty of breathing in water.

Dispersal

Some of the insects found in the fresh water environment live there only in certain life stages. For example dragonflies live underwater in their juvenile stages (known as nymphs), where they are active predators. As adults they are very active aerial predators, but tend to remain in the vicinity of the breeding sites. Water beetles are typically aquatic as both larvae and as adults.

Breathing

Aquatic insects need to breathe, and can take one of two approaches. Some, such as dragonfly larvae, have gills through which oxygen is absorbed from the water. Others breathe air, either by returning to the surface periodically to replenish supplies (for example diving beetles), or by maintaining a connection with the air through breathing tubes, such as mosquito larvae.
The web resource ARKive has a wealth of images and background information on many aquatic invertebrates.

Here are some of the animals you may find in your pond:

Insects on the surface

Pond skaters: Small animals, such as insects, find the surface of water quite a barrier because of surface tension. This also has the advantage that some insects, such as pond skaters can move around the surface by effectively walking on the water surface. Pond skaters are hunters - they run along the water surface predating on other small animals that fall onto the surface.
Arkive has pictures of pondskaters.

Whirligig beetles are aquatic beetles that can be seen swimming on the surface of pools of water. They are well adapted to this lifestyle: their eyes are split into two parts, one for looking below the surface, and one for looking above.
Image of the whirligig beetle from Texas A&M University collection.

Insects hanging from the surface

Mosquitoes breed in water, and their larvae can often be seen in standing water, hanging by their breathing tubes from the water surface. Mosquito larvae are filter feeders, eating small particles such as algae and bacteria suspended in the water. If you carry out the Water Bowl activity on the Life in the Undergrowth wall planner, you are very likely to see mosquito larvae at some stage.

Much larger than mosquito larvae, water boatmen swim just under the surface, often diving deeper. They are well named, as their hind legs are long and equipped with bristles in a paddle shape. Water boatmen are true bugs, and as adults can fly, which permits colonisation of new bodies of water.
Water boatmen pictures from ARKive.

Insects under the water

Water beetles, e.g. Dytiscus: The great diving beetle is an active predator. It carries air under its wing cases. The adult beetles are good fliers, and this helps their dispersal from one pond or river to another.
ARKive have Dytiscus beetle images.

Caddis fly larvae: Caddis flies are pretty inconspicuous insects. However their larvae, found generally in streams, are notable for the habit of constructing a protective tube from pieces of sand, gravel, vegetation, etc. This tube acts both as protection from predators, and as camouflage (since the tube is constructed from surrounding materials). Interestingly, fossil caddis fly cases are known!

Stonefly larvae: Stonefly larvae live under stones in streams, and like caddis fly and mayfly larvae breathe through gills. The adults are winged, and can be seen near streams.

Mayfly larvae: Mayflies are not true flies – they have two pairs of wings. The adult stages of these insects are very short-lived: they do not feed and survive only long enough to mate and lay eggs. The juvenile stages, or nymphs, live under stones in streams, breathing through gills. One of the characteristic features of both adult and juvenile stages are the three tails projecting from the tip of the abdomen.
Mayfly larvae photos from ARKive.

Dragonfly/damselfly larvae: Damselflies and dragonflies are closely related insects. The juvenile forms live underwater in streams and ponds, where they are active predators, feeding on other small invertebrates and even small fish. Some species of dragonfly spend up to 5 years as the juvenile aquatic form, before emerging as the mature adult. As adults, dragonflies are very conspicuous as they whizz around at great speed catching flies and other insects. Damselflies resemble dragonflies, but are generally rather more slender, and hold their wings back along their bodies when at rest.

Dragonflies are rather territorial, and can be seen undertaking some quite breathtaking aerobatics as they hunt, chase off competitors and mate. Eggs are laid in water, sometimes attached to vegetation.

If you'd like to experience pond life without getting your hands wet, why not try a Virtual pond dip?

Other arthropods

There are a number of small crustaceans that live in ponds and streams. Isopods look a little like woodlice, and are often known as waterlice. They inhabit the litter at the bottom of ponds and rivers. Daphnia and Cyclops are small (about 1mm) crustaceans that swim about in water, feeding on small organic objects.

Few spiders have colonised water. The major exception is the water spider. Rather than breathing through gills, water spiders make a bell-shaped web under water to hold air that they carry down on their bodies.
More on the water spider from Nature Grid.

Other invertebrates

Snails, such as Ramshorn snails, are herbivorous animals, that graze on algae using serrated mouthparts known as the radula.
Naturegrid offers more on ramshorn snails

There are a number of aquatic worms. Small leeches are frequently found when dipping pond and streams – these generally feed by attaching themselves to other animals and sucking blood or other fluids.

Medicinal leeches (so-called because they were used to bleed patients) are quite rare nowadays.
For More on leeches, see Nature Grid, while ARKive has images of medicinal leeches.

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