Odonata (dragonflies and damselflies)

Odonata Order Description

The Odonata family consists of the familiar damselflies and dragonflies. Adult damselflies are also commonly referred to as devil’s darning needles, and larval dragonflies are sometimes inappropriately described as hellgrammites (true hellgrammites are in the order Megaloptera). The Odonata family is divided into two suborders, the dragonflies (Anisoptera) and the damselflies (Zygoptera). Adult members of the Odonata order are often seen as iridescent flecks of color over still water ponds and slow moving streams. Adult damselflies and dragonflies can be easily distinguished by how the wings are held. Damselflies (Zygoptera) fold their wings behind their back, while dragonflies (Anisoptera) hold their wings open and perpendicular to their bodies while at rest.

Odonata Families:
Click on each to display information below .


CalopterygidaeFamily Calopterygidae

Broad-Winged Damselflies

These damselflies are most often found near slow moving streams resting on overhanging grasses and sedges. They have green or blue iridescent bodies roughly 30-40 mm in length with a contrasting black pair of wings. Species of Calopterygidae may be identified by having a first antennae segment longer or equal in size to the remaining antennae. The larvae may be distinguished from those of dragonflies by three leaf-like gills at the end of the abdomen, and are often found burrowed in the substrate in still or slow moving water.

Odonata Life stage history
Like most members of the subclass Insecta, the Odonata larval stage is completely aquatic. The larvae possess a unique large lower lip that covers the mouth parts and the majority of the insect’s head when viewed ventrally (from the belly-side). Odonata larvae pass through 10-15 instars, meaning that they will molt 10-15 times before emerging as a winged adult. The molts, or exuviae, from emerging larvae are often seen attached on the stems of grasses near the water’s edge. Respiration in Anisoptera or dragonfly larvae is primarily through rectum. Muscle contractions and relaxations in the rectum pump air into and out of the anus. The air pumping capabilities of the rectum also serve as an emergency avoidance mechanism. Air can be quickly forced out of the rectum to project the larva away from a potential danger. In Zygoptera larvae, or damselflies, oxygen is mainly obtained from diffusion through the skin and gills.

The adults in both suborders have two pairs of wings; in general, the dragonflies will hold their wings at rest horizontally, and the damselflies will fold their wings behind the body while at rest. The adult form is long and slender, and the body length of most adults is between 15 and 120mm. The adults of both suborders live out of the water, but Odonata adults hunt for water-dwelling prey and lay eggs on the surface of the water. Some dragonfly and damselfly adults also possess a unique ventilation behavior that includes thoracic and abdominal pumping. Thoracic pumping occurs when the muscles of the thorax contract in flight, consequently increasing and decreasing the size of the thoracic box and forcing air in and out of the thoracic air sacs. The second respiratory mechanism, abdominal pumping, involves the contraction and relaxation of the abdominal muscles. This muscle action forces air into and out of the abdominal air sacs.

Feeding habits
Both larvae and adults are predatory insects. Odonata larvae extend their unique large lower lip in front of the body to catch prey which may include small fish, tadpoles, or even other dragonfly or damselfly larva. Some species use a sit and wait ambush prey capture strategy, while others will actively stalk prey. The strategy used varies amongst prey species as well as prey and predator density. Adults feed primarily on terrestrial flying insects that they catch prey while in flight.

Ecological importance
Due to their low predatory position on the aquatic food chain, counts of Odonata populations are useful for determining the health of aquatic ecosystems. Changes in health of the aquatic ecosystems are more quickly identified by animals lower on the food chain than changes in populations of larger mammals or top predators. Some national parks in the United States are beginning to consider population counts of Odonata species when devising new management techiniques.

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