Megalopterans begin their lives hanging over water. Females lay egg masses on leaves, branches, or other surfaces over ponds and streams. When the larvae hatch, they fall into the water. Megalopteran larvae fend for themselves immediately, taking shelter under rocks or sand. The larvae are important members of aquatic food webs, feeding on worms and other insect larvae and preyed upon by fishes and other aquatic predators. It takes a few years for Megalopteran larvae to grow up, and they shed their skin (molt) each time they get too big for it. When at their adult size, they crawl out of the water. They pupate inside burrows under soil or dead leaves on the shoreline. Within just a few days, metamorphosis occurs, and a winged adult megalopteran emerges. The adults live just a few hours or, at most, a few days, during which they don't eat but do try to mate.

Insects are by far the most diverse and abundant group of organisms on Earth. More than one million insect species have been identified, and estimates of how many species exist range into the tens of millions. Insects got their start way back, in the Paleozoic (about 500 million years ago) and have evolved in tandem with flowers (coevolution). Insects have become specialized on particular flowers, leading to complex sets of adaptations that couple them in a feeding and pollination relationship (a mutualism). Specialization allows for many types of insects to live in the same habitat, accommodating their exceptional biodiversity. In a backyard in the temperate zone, one might find several thousand species of insects. Specialization can occur within one plant species as well, with different insects using different parts of the plant. In just one species of tropical tree, Dr. Terry Erwin of Smithsonian's National Museum of Natural History found about a thousand species of beetles.