< of spring term upon us, the familiar sights and sounds of summer have returned to the Arboretum: the singing of birds, the chattering of squirrels, the raucous yelling from bonfires on the Hill of Three Oaks. But there are other things that we notice more passively, like the flight of dragonflies, for example. Many of us will be familiar with the sentry-like flight of dragonflies over open areas on a summer evening, but few of us are familiar with the Odyssean struggle taking place in our lakes, ponds, and rivers that allow dragonflies to enjoy a brief moment of terrestrial sunshine at the end of their lives.
Once deposited as an egg in some submerged aquatic vegetation, dragonfly larvae, or nymphs, go through 6-15 instars (different phases of life characterized by changing body structure), that can take anywhere from two months to six years, usually taking about three years. During the nymph stage, dragonflies are vulnerable to predation by many fish, amphibians, and reptiles. Despite the veritable army of carnivorous beasts that long to devour them at every turn, dragonfly nymphs still find enough aquatic insect food themselves to survive their time underwater. They will even eat one another in the race for survival.
Once they reach maturity and the water temperature is sufficiently warm, nymphs crawl up onto aquatic vegetation and shed a hard shell that kept them protected underwater. Their wings begin to uncurl and harden, their abdomens decompress and lengthen, their eyes dry out and take on magnificent colors. But the danger has not yet passed. As their wings harden, dragonflies are poor fliers, and are most vulnerable to predation by frogs, toads, birds and especially other dragonflies. Migratory species like the Green Darner (Anax Junius) arrive in Minnesota as soon as the weather permits, usually in early April, when they can barely find enough calories to survive. By mid-may, as other species begin to emerge, the Darners enjoy a smorgasbord of emerging skimmers (family Libellulidae), which are smaller and clumsier.
Just the other morning as I walked around the retention pond I witnessed a toad snap up a recently emerged dragonfly in an instant. This gruesome scene captured the harsh realities of dragonfly life. The dragonfly, a beautifully painted species of clubtail (family Gomphidae) had endured years in the retention pond only to be eaten within hours of its first flight.