Pond Life 3 - The Blue Dasher



Blue dasher, male

This is Blue Dasher Week at the pond. Their numbers have been building for weeks, but now the air is filled with them. 

Nearly 30,000 lenses make up its compound eye, the dragonfly a 360-degree field of vision.

On the fly

Dragonflies can fly forward at about one hundred  body-lengths per second, and backwards at about three body-lengths per second. They are also capable of hovering in the air for about a minute.

With Yellow iris (Iris pseudacorus)

Males protect their shoreline breeding territories. They rise up to investigate intruders, chasing away other males.

Blue dasher, female

Females usually perch on upland vegetation and approach the water only when they are ready to mate.

Depositing eggs while hovering

After mating, the female oviposits her eggs by dipping the tip of her abdomen onto aquatic vegetation.

A vacated nymph case

Most of the dragonfly's life will be spent submerged in a larval stage.  Dragonfly nymphs are fierce predators. Their diet includes other aquatic larvae, small fish, and tadpoles.

An emergent adult with nymph case

Most of the Blue dasher's life is sent in the larval stage where it molts from six to fifteen times over the course of a year or two. In the early hours of a summer morning it crawls up out of the water onto a firm plant base to molt one last time, emerging from its old skin as an adult with functional wings.

The new adult spreading its wings

Although distinguishing species pattern markings are not yet apparent, this new adult is almost certainly a Blue dasher. It flew away within an hour.

The 'obelisk' position

On warmer days Blue dashers raise their abdomens a vertical 'obelisk' position, like a handstand, apparently reducing heat absorbance.

A water lily perch

They hunt by keeping still and waiting for small insect prey to come within range, then darting out to catch it.

Blue dasher on pickerelweed flower

The science of dragonfly flight

When hovering, the dragonfly's wings stroke back and down independently in a kind of rowing motion that creates vortices of air and upward drag. Complex fluid dynamics are instrumental in keeping its body stationary. The efficiency of the wings is increased by their capacity to flex and twist with the air. This natural action conserves energy that the insect would otherwise have to use to effect such turns by exercising muscles. The wings in the foreground also show a solidly colored (dark) cell called a pterostigma,  which by its slightly heavier construction helps dampen vibrations and assists in gliding.

From the Universities Space Research Association's website.