A strong flier (3), the adult lake darner may be active throughout the day and continue flying until dark (2). In the far north of its range, it may even be active under the midnight sun (2) (5). Like other darner species, the lake darner hangs in a characteristic vertical position when perched (2) (5), but unlike most other darners it does not hover during flight (2) (6).
The male lake darner is not territorial, and it flies over open water or along lake shores in search of females with which to mate. It usually avoids entering vegetation, except when searching for a female (2) (6). As in other dragonflies, the male lake darner may guard the female while the eggs are laid, to prevent her from mating with other males (8) (9).
The female lake darner has a well-developed ovipositor, a tube-like structure at the end of the abdomen which is used to lay the eggs. As in other Aeshnidae species, the female lake darner is able to use the ovipositor to slice into water plants and lay eggs one at a time into the stems (2) (3) (5) (6). The eggs are also sometimes laid onto floating logs or in root tangles at or just below the water’s surface (2) (6).
The larvae of the lake darner, known as nymphs, have a streamlined body shape and excellent eyesight. They are opportunistic and voracious predators, often climbing aquatic vegetation to stalk their prey and attacking any animal smaller than themselves (3), including insect larvae, small crustaceans, tadpoles and even small fish (6) (8). As in all dragonflies, the larva of the lake darner catches its prey by shooting out the fiercely hooked lower jaw, known as the labium, which impales the victim and drags it back to the mouth (8) (9). The larvae of most Aeshna species take about two to four years to develop into adults (3).
The flight season of the lake darner, when the adults emerge and are active, usually runs from June to October (2) (3) (4) (5). Like the larva, the adult lake darner is an opportunistic predator and will catch almost any soft-bodied flying insect (6).