Different Kinds of Aquatic Insects

Different Kinds of Aquatic Insects

Mayflies (Order: Ephemeroptera)

Mayfly hatches are a dry fly fisherperson’s dream. A large hatch looks like a ton of mini sailboats floating gracefully on the surface of the water. Mayflies can be found in both still water and moving streams. The best mayfly hatches are often in spring and fall; however, hatches can occur at many different times of the year. Trout key into the hatches but a well-presented mayfly nymph will get attention most of the time. Most mayflies are around size 16 but some can be as small as size 22 (Baetis) or as big as a size 4 (Hexagenia). All mayflies start out as an egg in a water body. The egg then develops into a nymph, a small insect living under the surface of the water. The nymphs consume detritus, living plant material, and some predate on other aquatic insects. Mayfly nymphs go through several “molts” or instars before reaching the stage when they are ready to become adults. Once the conditions in the water and on the surface are prime, the nymphs rise up into the surface film of water. In the surface film, the mayflies shed their old nymph husk and become adult mayflies with wings. Some individuals get stuck in their nymph husk, these are called crippled mayflies. Trout love the easy meal cripples provide. Adult mayflies are unable to fly immediately, dun is the word that describes this stage of adulthood. Trout gorge themselves on vulnerable duns. The life span of an adult mayfly is short. Once the duns take off they mate and die en masse. During this stage, the mayflies are called spinners. Mayfly spinner falls offer trout another great opportunity to fatten up on mayflies.

Mayflies are very diverse. Stop in at your local fly shop to find specifics on the common mayflies in your local fisheries. 

Stoneflies (Order: Plecoptera)

Stoneflies are an important food source for trout at all times of the year. In the spring and sometimes fall, stoneflies are scattered all over the bank-side vegetation. During the winter, stonefly nymphs are all over the bottom of the river and provide trout with a consistent food source. Stoneflies can be found in still and moving water. They typically live on the stones at the bottom of a waterbody; although, some live in the hyporheic zone, an area of saturated soil underneath a river or lake bed. As with mayflies, the life cycle starts with an egg. A nymph hatches out of the egg. Stonefly nymphs have several different instar (molt) stages. Detritus, living plant material, and other aquatic insects are consumed by stonefly nymphs. When water and surface conditions are ideal, stoneflies crawl onto rocks, vegetation, and other things along the streamside to metamorphosis into their adult stage. Adult stoneflies are clumsy and they often fall into the water, where they are picked off by trout. Stoneflies have a huge range of sizes, some are as small as size 20 while salmon flies can be as big as a size 2. There’s nothing quite like watching a trout smash a large stonefly on the surface.

Stonefly hatches occur at specific times on many rivers. Check-in at a local fly shop to check when the hatches will start to happen on your local river.

Caddisflies (Order: Tricoptera)

Caddisflies are an incredibly diverse group of aquatic insects. Most caddis species live in streams, there are much fewer species that have adapted for life in still water. Caddis larva are capable of creating cases that protect them from predators and harsh stream currents. Not all caddis species create cases, some spin webs to collect food, some create small shelters and others live freely in the river, like stonefly and mayfly nymphs. The life cycle of caddis starts with an egg. Larva emerge from the eggs. Larva consume detritus, living plant material, and other aquatic insects. The larva develop into pupa. Pupae drift in the current until the optimal water conditions are found for metamorphosis. Sometimes pupa will drift miles downstream until the right water conditions are found. Because of this, the pupa are easy prey for trout. Pupa rapidly transform into adults, there is only a brief moment where the adult caddisfly stays on the surface of the water. Adult caddisflies can live for multiple days but after they mate and reproduce they die. Typically caddis are around size 18-14 but some can be nearly microscopic and others can be as big as a size 8.

The huge diversity of caddisflies is overwhelming. If you need help narrowing down your flies of choice, head into a local fly shop and they’ll help you slim down your choices.

Dragon and Damsel Flies (Order: Odonata)

Dragonflies (suborder: Anisoptera) and damselflies (suborder: Zygoptera) are some of the oldest aquatic insects still living on the planet. Most insects of the order Odonata live in still water environments. Their life cycle starts with an egg that contains a nymph. Unlike other aquatic insects, Odonata nymphs are almost completely predatory. They utilize an extendable jaw to capture other aquatic insects, amphibians, and even small fish. Once mature, the nymphs crawl onto vegetation, logs, and rocks near the water body and then morph into adults. Adult Odonata are agile fliers that hunt other flying insects. Typically, anglers imitate Odonata nymphs because they are the most readily available to trout. Damselfly nymphs are very important for fishing at the Cascade Lakes. Sometimes a spent dragon or damselfly adult will get the attention of a large trout. 

The tactics used to effectively imitate Odonata can be difficult to learn. If you need help learning the ropes, ask us or your local fly shop for assistance. 

True Flies (Order: Diptera)

The order Diptera contains all true flies. Generally, fly fisherpeople will imitate chironomids (midges) and sometimes cranefly larva but there are many more types of aquatic true flies. The diversity of the Diptera order is mind-boggling. Aquatic and non-aquatic Diptera is one of the most prominent orders of organisms on the entire planet. For simplicity, I’ll describe the basic life cycle that most chironomids exhibit. As with all other aquatic insects, an egg is the first step. A larva emerges from the egg, which then spends time collecting and gathering organic matter to consume. The larva becomes a pupa which then elevates to the surface of the water to become an adult. Trout will typically key into chironomid larva and pupa but sometimes in the winter, the adults are also on the menu. Chironomids are generally small, as are many Diptera species, although some can be large such as craneflies. There are many different families of Diptera besides Chironomids. If you’d like to learn more about Diptera, macroinvertebrates.org is a great place to start. 

There are many more orders of aquatic insects besides Ephemeroptera, Plecotera, Tricoptera, Odonata, and Diptera. Coleoptera (beetles), Hemiptera (true bugs, e.g. water skimmer and water boatman), and Lepidoptera (moths) are just a few of the other orders of aquatic insects. Of course, it is not necessary to have a degree in entomology to be a great fly fisher; however, a basic understanding of the different types of aquatic insects will prove useful out on the water. 

Older Post
Newer Post

Leave a comment

Please note, comments must be approved before they are published

Close (esc)

Sign Up For Our newsletter

Stay in tune with what is happening in Central Oregon and with Fly & Field Outfitters. Don't worry, we will not send you too many emails!

Age verification

By clicking enter you are verifying that you are old enough to consume alcohol.


Your cart is currently empty.
Shop now
Book Now Book Now