Aquatic insect life

We usually think of insects as being animals of the land, but did you know that many insects spend part of their lives in water? Some spend all their early life underwater while others are just great swimmers.

Aquatic larvae

The larvae of some insects live entirely underwater. These larvae often look quite different from their adult forms and have gills to help them ‘breathe’ underwater. Insects with aquatic larvae include mosquitoes, stoneflies and dragonflies. Because their larvae are aquatic, you can often find the adults flying near rivers and ponds as well.

Habitat

You will find different species of insect larvae in different types of rivers or ponds. Some insects are only able to survive in clean flowing waterways, rivers and streams while others can survive in still or polluted water. Scientists can measure the quality of a waterway based on what insects they find living in and near it. This is called the macroinvertebrate community index.

Swimmers

Some insects have entirely terrestrial life cycles but may still enter the water to feed. These insects tend to be found in slow-moving streams, ponds and lakes and even water troughs.

Unlike aquatic larvae, these adult insects do not have gills and so cannot breathe underwater. Insects don’t have lungs like humans do. Instead, they take in oxygen through tiny holes or spiracles along the sides of their bodies when they are at the surface. But this doesn’t stop water boatmen or diving beetles from being great swimmers. When these insects dive underwater, they trap air against their spiracles and use it to breathe, a bit like an oxygen tank. In a way, they’re literally holding their breath!

Human impacts

Like our native fish and other freshwater macroinvertebrates, our aquatic insects have been adversely impacted by human activity. They make good bioindicators of the quality of water in rivers and ponds as many rely on high-quality water to fully develop their larval stages in their life cycles.

These two teacher resources have practical information for restoring streams for native fish: Planning for change and Planting stream edges. These could be adapted when looking at aquatic insects, as a healthy environment for fish also means a healthy environment for these insects.