Dragonflies and Damselflies

Dragonfly 2

Dragonflies and damselflies (Order Odonata) are ancient creatures that have been around for about 250 million years. Both have very large eyes relative to body size compared to other insects. Dragonflies have a relatively wide thorax and hold their wings horizontally when perched. Damselflies have a slender thorax and hold their wings folded when perched. There are more than 5,000 species worldwide and about 400 species in North America.

The Order name, Odonata, means “toothed ones.” This refers to a prehensile lip-like structure in both nymphs and adults that can be extended forward very quickly to catch prey.

“Both dragonflies and damselflies begin their lives in the water. Dragonfly eggs are round and about 0.5 mm long, whereas damselfly eggs are cylindrical and longer, about 1 mm long. Similarly, the nymphs (larvae) of the two groups differ. A larval damselfly abdomen is longer and narrower with three fin-like gills projecting from the end. Dragonfly nymphs are shorter and bulkier, and the gills are located inside the abdomen. The dragonfly nymph expands and contracts its abdomen to move water over its gills, and can squeeze the water out rapidly for a short burst of underwater jet propulsion.” (Berkeley)

See photos of nymphs from the Dragonfly Woman blog here.

During the nymph stage, which can last two to three years and involve up to 15 molts, dragonflies and damselflies prey upon other insects, small fish, small tadpoles, and anything else they can catch.

The adults:

According to Berkeley:

Both dragonflies and damselflies have two pairs of elongated membranous wings with a strong cross vein and many small veins that criss-cross in the wings, adding strength and flexibility to the wings. Both groups also have a characteristic nodus, or notch, in the front edge of each wing. In dragonflies, the rear wings have a broader base and are larger than the front pair. Damselflies, by contrast, have front and hind wings similar in shape, and as a result they fly slower than dragonflies do. Also, dragonflies do not have hinges enabling them to fold their wings together when resting, though damselflies do. This feature of the wings is the key morphological feature distinguishing adult dragonflies from damselflies.

“Dragonflies can fly forward at about 100 body-lengths per second, and backwards at about 3 body-lengths per second. They are also capable of hovering in the air for about a minute. Longer periods of stagnant flight would interfere with thermoregulation. The wings of male dragoinflies are relatively longer and narrower than females in large species. Adult wingspans measure from 17 millimeters (Agriocnemis) to 20 centimeters (Coerulatus). Most temperate zone species have wingspans of 5 to 8 centimeters and wings that are from two to twelve centimeters from front to back.

“Dragonflies are generalists, that is, they eat whatever suitable prey is abundant. Oftentimes, they hunt in groups where large numbers of termites or ants are flying, or near swarms of mayflies, caddisflies, or gnats. According to most studies, the main diet of adult odonates consists of small insects, especially Diptera (flies). Maturing dragonfly larvae feed very intensively, as do females when developing their eggs. Studies show that food shortage may limit reproductive behavior. Dragonflies do not hunt in cold weather. Damselflies, however, are not as limited by temperature and have been observed hunting during cold spells. Males are territorial, sometimes patrolling for prey for hours at a time.”

The life span of adult dragonflies and damselflies is measured in hours to months.

The Arizona-Sonora Desert Museum describes them as follows:

“No predator soup would be complete without dragonflies and damselflies, the entire Order Odonata being predaceous, both as adults and nymphs. Damselfly nymphs have 3 leaf-like gills protruding from the ends of their abdomens, while dragonfly nymphs have spiny posteriors that suck oxygenated water into their rectums where the oxygen is absorbed. Many nymphs dart through the water by rapidly forcing the water out of their rectums—jet propulsion! The Libellulidae are usually brightly-patterned nymphs that crawl across the bottom searching for prey, while the Gomphidae sit and wait for their victims to stumble by. One gomphid is a flattened insect (with wide, flat antennae as well) that sits on the bottom, while another gomphid hides just under the sand, waiting for vibrations to indicate prey coming by. Quiver your hand over clean, shallow sand and watch for movement of this hidden insect. Another dragonfly (Cordulegasteridae), more common in pools in small, rocky streams, is hairy and usually covered with foreign material, camouflaged and motionless, waiting for prey.

“Most damselfly nymphs are slender. The Calopterygidae perch on plants or tops of rocks on long legs; they snatch insects and small crustaceans in quiet pools. Another damselfly in the family Coenagrionidae, the only odonate common in flowing water, crawls through leaves and roots of slow runs. Its more compact shape protects it from vagaries of the current.

“The face of a damselfly or dragonfly nymph appears to be covered by a toothed mask. This is actually a retractable set of mouthparts that can extend instantly up to 2 to 3 head-lengths in front of the insect, then open sideways to grab a victim. You can readily pull this contraption outward to see how it functions; dragonfly nymphs are particularly sturdy.

“Odonata adults cruise the streamside in search of flying insects, which they capture “on the wing” with legs that are covered with long hairs forming basket traps. Dragonflies extend broad wings outward, while damselflies’ slender wings are held back over the body. Skimmers (family Libellulidae) sit on the tips of plants, darting out to catch flying insects. They also patrol stream margins to defend their feeding and reproductive territories against other dragonflies.

“Odonate mating and oviposition behaviors are also complex. A male may appear to be looped awkwardly behind a female, using the claspers at his tail end to hold her “neck,” while contacting the genital openings to pass sperm. Damselflies like Argia often fly in tandem, the blue male attached to the tan female with his claspers. To defend his genetic contribution from competing males, he stays attached while she oviposits eggs into algal mats and other soft streamside materials. There are even reports that males of some species have hooks for pulling out sperm deposited earlier in the female by another male! Many female dragonflies and some damselflies release their eggs on the wing, touching their abdomens to the water during the release, or dropping the eggs from the air like dive-bombers. The eggs drift downward, becoming sticky enough when wetted to adhere to the bottom.”

For many photos see:

Dragonflies: http://dragonflywebsite.com/dragonfly-slideshow.cfm

Damselflies: http://dragonflywebsite.com/damselfly-slideshow.cfm

The BBC has several videos here: http://www.bbc.co.uk/nature/life/Odonata


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