Dragonflies

By Jeff Morgan

Almost every schoolchild can recognize these large insects as the beautiful blue, green, and occasionally red iridescent insects that buzz around wherever there is standing water. Dragonflies do us a great service by keeping the hordes of mosquitoes and biting flies in check.

However, trout rarely feed on the beautiful adults, for the ugly nymphs are much more accessible. The nymphs are large (up to two inches), and are the Hannibal Lecters of the aquatic world, devouring anything that ambles before them, from beetles to baby brook trout.

The Big Mac of the Lake

The nutrient density of these insects is impressive and makes them a prime target of fish: one dragonfly nymph will provide more calories than hundreds of caddis larvae! This partially explains the vigor with which trout assault the imitations.

Dragonflies are not just an important food source for trout, they compose a significant portion of the insect diet of bass and of some large panfish. The once-legendary dragonfly population of Oregon's Crane Prairie Reservoir was doubtless a key factor in the success of the illegally-stocked bass in that water. In other lakes, I have found bass with over twenty dragonfly nymphs in their stomachs!

Waters with good dragonfly populations can grow large trout with ease, so it pays to understand the biology of these insects.

Nymphs

Dragonflies are spread throughout most of the West's trout lakes, and many of the slower parts of the rivers, too. River species generally hold directly on the bottom in deep pools, hidden in the substrate, and only move to pounce on food. Given the negligible currents in these areas, and the ability of the nymphs to jet-propel themselves by shooting water out their butt, these nymphs seldom enter the drift. For this reason, we will focus our efforts on dragonflies in lakes.

The nymphs are the most important stage for anglers, for the adults rarely land on the water for long periods of times. The nymphs prefer weedy and woody structure near the bottom of shallow areas. They like this cover because it conceals them from their prey, which is just about anything that swims. Mayfly nymphs, water beetles, leeches, tadpoles, smaller dragonfly and damselfly nymphs, and even small fish are not safe from these voracious predators.

The nymphs commonly grow to about 18-50 mm in length before they emerge, and they live underwater 12-16 months before they mature into adults. Dragonfly nymphs propel themselves through a mini jet-propulsion system: they take in water and expel it out the end of their abdomens. This shoots the nymphs forward in four- to twelve-inch bursts. The longer bursts, however, are often reserved for pursuing prey or fleeing an enemy. This jet-propulsion system is very important to anglers, because a bug of that size moving that fast catches the eye of nearby fish. Trout are quick to pounce on this prey lest it escape.

Unfortunately for anglers, dragonfly nymphs are usually stationary, waiting to ambush their prey. The nymphs are much more available when migrating towards the logs, rocks, and reeds near shoreline on which they climb out of the water to emerge. This migration takes place usually between May and July, and this is the prime time to throw dragonfly nymphs.

There are many families of dragonflies in the West, but because of similar habits, habitat, and body structure, this diversity can be whittled down to two primary families of importance to the angler: Aeshnidae and Libellulidae.

Aeshnidae Family

The larvae of the most important family, Aeshnidae, are streamlined, though still pleasingly plump, and are prevalent in weedy waters. They are usually found in shades of olive (though occasionally brownish) and they are the largest of the dragonflies in the West, approaching two inches in length as a mature nymph.

These nymphs are the most important to the angler because of their active feeding nature. They are perpetually hunting aquatic insects, annelids, and small fish, and this exposure makes them prime targets for a cruising trout.

The genera Aeshna and Anax are generally the most common aeschnids throughout the West. Their emergence period is extensive, from late spring through early fall, so nymph imitations are a viable option throughout the season. The adults feed on mosquitoes and other aerial insects, and lay their eggs on exposed vegetation. Thus they are not available to trout when ovipositing.

Libellulidae Family

This second family of dragonflies is more stubby and stout, and it prefers to make its dwelling among rocks and logs. Though libellulids are commonly found in mottled shades of brown and dark olive, they can adapt to the color of its surroundings. These dragonflies are generally shorter than the aeshnids, ranging from 8 to 30 mm in length when mature.

This family rarely is found in open water cruising for prey. Rather, they burrow into the mud on the bottom to camouflage themselves from their prey, which like the Aeschnids, consists primarily of small insects and small fish. They grasp their prey by shooting out their extendable, spoon-shaped labium (bottom jaw), grasping the prey, and retracting the jaw. Due to their feeding habits, Libellulidae are best imitated very close to the bottom. These dragonflies are very widespread and are tolerant of a wide array of water conditions, but they are almost always found in stillwaters.

Adults

Dragonfly adults are among the most beautiful of all insects, and many non-anglers are quite fascinated with them. They also serve as a great distraction when the fishing is miserable! Despite their large size and proximity to water, I have never seen a trout eat one of the adults buzzing on the surface. On the other hand, spent adults sometimes are found sprawled on the surface. Trout may feed eagerly on them at that time.

Patterns and Presentations

Randall Kaufmann's Lake Dragon is a commonly-used, widely-available nymph pattern. It imitates the more slender nymphs of the Aeshnidae family. Present the fly on a sinking line and with a retrieve that matches the natural insect's motions: a two or four inch pull, followed by a pause, then another short pull; a very slow crawl; a quick 12-inch pull, followed by a long pause.

Spent adult dragonflies are rarely tied and are seldom commercially available. However, you can tie on in a manner similar to the Stalcup Adult Damselfly . Use a thicker body and a bigger fly. The pattern is presented with a floating line. Let it sit until something happens. Or doesn't.

Jeff Morgan has written many articles for Westfly, mostly on entomology and fly tying. He is the author of An Angler's Guide to the Oregon Cascades and Small Stream Fly Fishing.