The insect order Odonata encompasses the familiar dragonflies and damselflies. The name Odonata translates to “toothed ones,” a reference to the serrated mandibles of these predatory insects. They represent an ancient lineage of flying insects linked to aquatic environments, as they spend a significant portion of their lives in water before emerging as winged adults.
Distinguishing Dragonflies and Damselflies
Though often mistaken for one another, dragonflies and damselflies can be distinguished by observing a few physical and behavioral traits. Dragonflies, belonging to the suborder Anisoptera, typically have a more robust and bulky body structure. In contrast, damselflies, from the suborder Zygoptera, are characterized by their slender, more delicate build.
A primary identifier is the structure and placement of their eyes. Dragonflies possess very large compound eyes that are so extensive they often meet at the top of the head, providing them with a nearly 360-degree field of vision. Damselfly eyes, while also large, are smaller by comparison and are always distinctly separated, positioned on the sides of a more mobile, bar-shaped head.
The way they hold their wings at rest is an easily observed difference. Dragonflies are unable to fold their wings back and will hold them outstretched and perpendicular to their bodies, like an airplane. Damselflies, however, typically fold their wings together, holding them parallel to the body and over the abdomen when perched.
These physical variations influence their flight capabilities. Dragonflies are powerful and agile fliers, known for their high-speed pursuits and acrobatic maneuvers. Damselflies exhibit a more fluttery and less direct flight.
The Aquatic Life of Odonata
The life cycle of Odonata is split between an aquatic juvenile stage and a terrestrial adult stage. The majority of an odonate’s life is spent underwater as a nymph, also known as a naiad. This aquatic phase can last from a few months in some species to several years in others, depending on the species and environmental conditions like water temperature.
The life cycle begins when eggs are laid in or near water, often on aquatic plants. Upon hatching, the nymph emerges as a voracious aquatic predator, feeding on a wide range of prey including other aquatic invertebrates, tadpoles, and even small fish. They capture this prey using a unique, extendable lower jaw called a labium, which shoots out to grasp victims.
Nymphs breathe through gills, but the location differs between the two suborders. Dragonfly nymphs have internal gills located within their rectum, breathing by drawing water in and out. Damselfly nymphs possess three external, feather-like gills at the end of their abdomen. When development is complete, the nymph crawls out of the water onto vegetation or a rock, where the adult insect emerges from the nymphal exoskeleton, a process called eclosure.
Ecological Significance
As predators in both their aquatic and aerial forms, Odonata help regulate the populations of other insects. In their nymphal stage, they consume large numbers of aquatic invertebrates, which can include the larvae of mosquitoes. As flying adults, they are skilled aerial hunters, catching and eating other flying insects such as mosquitoes, gnats, and flies.
While they are effective predators, they also serve as a food source for a variety of other animals. Fish, frogs, turtles, and larger predatory aquatic insects prey on the nymphs underwater. Once they emerge as adults, Odonata are hunted by birds, spiders, and even larger dragonflies. This dual role places them in the middle of the food web.
The presence and diversity of Odonata species are often used as bioindicators of freshwater ecosystem health. Their nymphs require clean, well-oxygenated water to survive and are sensitive to pollutants like pesticides. A thriving and varied community of dragonflies and damselflies signals a healthy, unpolluted aquatic environment.