Dragonflies are a common sight near water, known for their agile flight and striking appearance. Their life cycle involves a fascinating transformation process, known as metamorphosis. Dragonflies undergo incomplete metamorphosis, a developmental pathway that differs significantly from the more commonly recognized complete metamorphosis seen in insects like butterflies. Their journey from egg to adult unfolds in a series of gradual changes.
Defining Metamorphosis Types
Insect metamorphosis falls into two main categories: complete and incomplete. Complete metamorphosis involves four distinct stages: egg, larva, pupa, and adult. The larval stage, such as a caterpillar, looks vastly different from the adult, and a transitional pupal stage facilitates this dramatic change. Butterflies exemplify complete metamorphosis, where the larva transforms into a pupa before emerging as a winged adult.
In contrast, incomplete metamorphosis progresses through three stages: egg, nymph, and adult. The nymph generally resembles a smaller version of the adult, though it lacks fully developed wings. Growth occurs through a series of molts, where the nymph sheds its exoskeleton. There is no pupal stage in incomplete metamorphosis.
Dragonfly’s Developmental Journey
A dragonfly’s life begins as an egg, which the female typically lays in or near water, often on aquatic plants or in mud. Some species lay elongated eggs into plant material, while others deposit round, jelly-like eggs loosely into the water. These eggs usually hatch within one to five weeks, depending on the species and environmental conditions. Eggs laid late in the season may overwinter and hatch the following spring.
Upon hatching, a small aquatic nymph emerges. This nymph stage is spent entirely underwater and constitutes the longest portion of a dragonfly’s life, lasting from a few months to several years. Dragonfly nymphs are predatory, equipped with specialized hinged jaws to capture small aquatic prey like insect larvae, crustaceans, and even small fish. They breathe through gills, with some species using internal rectal gills that also allow for jet propulsion by expelling water.
As the nymph grows, it undergoes multiple molts, shedding its exoskeleton between 5 to 17 times, commonly around 12. During later nymphal stages, wing pads become visible, which are external buds containing the developing adult wings. When fully grown, the nymph crawls out of the water onto emergent vegetation or another stable surface. The exoskeleton then splits, and the adult dragonfly slowly emerges, leaving behind its shed nymphal skin, called an exuvia. The newly emerged adult, known as a teneral, is initially pale and has soft, crumpled wings that gradually expand and harden over several hours as body fluids are pumped into them.
Why Dragonfly Metamorphosis is Incomplete
Dragonfly metamorphosis is classified as incomplete because it lacks a pupal stage. Instead, the nymph directly develops into the adult form after its final molt. While adapted for an aquatic lifestyle, the nymph shares a general resemblance to the adult, possessing similar body structures like six legs and compound eyes, though it lacks functional wings. The gradual development of adult features, such as visible wing pads, highlights this direct growth pattern.