The dragonfly is a striking insect belonging to the order Odonata, which also includes the closely related damselflies. As formidable aerial predators, they are well-known for their powerful, agile flight and often brilliant coloration. This guide details the physical characteristics that define the adult dragonfly.
Defining Characteristics: The Head and Eyes
The most distinctive feature of the dragonfly’s appearance is its head, which is almost entirely dominated by two enormous compound eyes. These eyes typically meet or nearly meet at the top of the head, wrapping around to provide a nearly panoramic, 360-degree field of vision. Each large eye is composed of up to 30,000 individual light-sensing units called ommatidia, enabling exceptional detection of movement.
The eye structure is often divided into a dorsal section, which focuses on light from above, and a ventral section, which focuses on objects below. The head also features small, inconspicuous antennae, thought to function primarily as wind-speed and direction sensors rather than for scent. The mouthparts, positioned on the front of the head, consist of strong, biting mandibles. The Greek root of the order name, Odonata, translates to “toothed ones,” a nod to these powerful jaws used to consume prey captured in flight. The head is also highly mobile, able to swivel and turn to compensate for the inability of the eyes themselves to move.
The Wings and Flight Structure
Dragonflies possess two pairs of large, membranous wings that are attached to the thorax. Unlike many other insects, the forewings and hindwings operate independently, contributing to the dragonfly’s highly maneuverable flight. The hindwings are generally broader at the base than the forewings, which aids in their powerful, straight-line flying ability.
The wings are supported by a dense network of veins, known as venation, which forms an intricate, species-specific pattern of enclosed cells. This venation provides both structural strength and flexibility, allowing the wing to passively twist and deform for optimal aerodynamics during flight. Near the leading edge of each wing is a small, darkened spot called the pterostigma. This pigmented area is believed to help stabilize flight by reducing flutter, acting as a mass damper at the wing’s tip. Dragonflies hold their wings spread out flat, perpendicular to their body, when at rest.
Body Structure: Thorax and Abdomen
The body of the dragonfly is composed of the three standard insect segments: the head, thorax, and abdomen. The thorax is a robust, box-like segment that serves as the power center, housing the large flight muscles and anchoring the two pairs of wings and three pairs of legs. The six legs are generally short, spiny, and directed forward, forming a basket-like trap used to scoop up flying insects mid-air.
Dragonflies rarely use their legs for walking, primarily reserving them for perching and manipulating prey. Extending from the thorax is the long, slender abdomen, which typically consists of ten distinct segments. The abdomen’s elongated shape helps stabilize the insect during flight and often displays vibrant, iridescent colors, such as metallic blues, greens, or reds. The terminal end of the abdomen in males features claspers used to hold the female during mating.
Key Differences from Damselflies
Though both belong to the order Odonata, dragonflies and damselflies have three consistent visual differences. Dragonflies are typically the more robust of the two, possessing a thicker, chunkier body compared to the slender, twig-like abdomen of a damselfly.
The appearance of the head offers a second clear distinction, as the large compound eyes of a dragonfly meet or nearly meet at the top of the head, leaving little to no gap between them. Damselflies, conversely, have eyes that are widely separated, giving their head a visual structure that is often described as dumbbell-shaped.
The most reliable way to tell them apart is by observing their wings when they are not flying. While a dragonfly holds its wings out to the side, a damselfly typically folds its wings together over its back, holding them parallel to the length of its abdomen.