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Aquatic Insects: Identification & Examples

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Most insects live on land, but there are many that spend some or all of their lives in the water. In this lesson, we'll explore the world of the aquatic insects, learn how to identify them, and see some examples of some of the more common ones.

What are Aquatic Insects?

Because they look so different, we sometimes forget that insects are part of the animal kingdom. But insects are really cool animals because they are such a diverse group. They are also the largest group of animals on Earth, with a possible 30 million species and 10 quintillion individuals. That's a 10 followed by 18 zeros!

A group of insects called aquatic insects are especially unique because they spend at least part of their lives in water. There are many different types of aquatic insects, and they have distinctive adaptations and features that allow them to thrive in this environment.

Features of Aquatic Insects

Aquatic insects have many features that you would expect to find on all insects. They have legs, a hard protective cover on the outside of the body called the exoskeleton, antennae, and eyes. Adult aquatic insects also have functional wings, but juvenile stages do not, which sometimes makes them look more like worms than insects. In fact, many of the aquatic insects have juvenile stages that look nothing at all like their adult counterparts.


Many of the aquatic insects, like this whirligig beetle, have juvenile and adult stages that look nothing alike
whirligig beetle


Adult aquatic insects have a unique look about them. Many are long and slender, like the dragonfly, and they are lightweight and able to whiz around ponds and lakes with ease. Others, like the stonefly, are fairly flat, making them stealthy on the water's surface. Many aquatic insects have long tails, which may occur in both the juvenile and adult stages.


Stoneflies are fairly flat aquatic insects with long wings down their back
stonefly


Like other animals that live in aquatic environments, aquatic insects are adapted to breathe oxygen that is dissolved in the water. Terrestrial insects have holes in their bodies called spiracles through which they breathe. While some aquatic insects have spiracles that they can close while underwater, in general, this isn't a useful feature for them for breathing. It would be like poking a bunch of holes in a closed container and then putting it underwater. So instead, many aquatic insects have gills that function like the gills of a fish. And other aquatic insects can simply exchange gas through their skin like earthworms do on land. Some aquatic insects have gotten very creative in how they breathe underwater and may take a bubble of air down with them to periodically breathe from, or they may even have a tube that sticks up out of the water like a snorkel!

Feeding

Aquatic insects can be categorized into groups called functional feeding groups that are based on the type of food they eat.

There are the collectors, which collect particles of decaying plant material. Some collectors shovel food into their mouths, others use long hairs on their legs and head to catch material floating by in the water, and others still use silk nets that collect floating material like a spider web collects insects.


Collectors like this caddisfly can create nets to catch plant material passing by
caddis fly and web


Predators are aquatic insects that eat other animals. These insects have special adaptations such as jaws, legs, and beaks that help them catch and eat their food. Small invertebrates such as fish and tadpoles are favorite snacks of predatory aquatic insects.

There are also the scrapers, which as the name implies, scrape food off of various surfaces. These aquatic insects have specially adapted mouthparts that work like a knife to scrape algae off of rocks.

Then there are the shredders, which devour plant material such as leaves, twigs, and flowers. They have specially adapted mouths that allow them to shred and grind up their food.

Examples of Aquatic Insects

While there are many different aquatic insects, there are some common critters that you are likely to see in your neighborhood pond or stream. Below is a list of some of the major aquatic insects, descriptions of what the adults look like, and interesting facts about the animals.

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