Pond Life 4 - Damselflies

Violet dancer and Eastern forktail

Around the edge of the pond, frequently hovering within the foliage, damselflies occupy a niche parallel to their heftier cousins the dragonflies that patrol the open air.

Damselflies catch and eat small insects. Often they pick their prey off low vegetation with their spiny legs.

Lilypad clubtail

At rest, most damselflies fold their wings together above their bodies.


Spotted spreadwing

An exception to this characteristic is the family of spreadwings, which hold their wings slightly apart when perched during daylight, at an angle away from their bodies. 

A Fragile forktail on a water lily pad

A damselfly's eyes are distinctively spherical, smaller and more widely separated from each other than on a dragonfly, whose eyes overlap. 

A male Familiar bluet

Male damselflies are often brightly colored. The absolute identification of species, however, may depend on close examination of patterns at the tip of the tail.


An unidentified female damselfly

Females are usually plainer, cryptically colored, and harder to identify.

An adult male Slender spreadwing

A damselfly's membranous fore and hind wings are similar in appearance. They are strengthened by longitudinal veins linked by many cross-veins. These are filled with a fluid analogous to blood that circulates in direct contact with its tissues.

A pair of Slender spreadwings at an early stage of mating

This mating pair will form a shape known as a "heart" or "wheel", the male clasping the female at the back of the head, the female curling her abdomen down to pick up sperm at the base of the male's abdomen. The pair may remain together with the male still clasping the female while she lays eggs within the tissue of plants in or near water using a robust ovipositor.

A probable Slender spreadwing emerging in adult form

Damselfly nymphs molt repeatedly during their underwater lives. This one has at last crawled out of the water, fixed itself to a water lily blossom, and undergone metamorphosis to adulthood. After its skin split down the back it emerged to inflate its wings and abdomen.

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.

Pond Life 2 - The Hunting Heron

This week I watched a Green heron masterfully working the pond's edge.

Its forward-directed eyes give it better binocular vision than most birds for pinpointing prey.

It can dart out of stillness like an arrow from a drawn bow.

It's ready when a tadpole surfaces momentarily for a breath.

After a while the heron changes strategy. It climbs stealthily into shrubbery at the far side of the pond. Suddenly its head snaps forward to pluck a dragonfly from the foliage.

Notice the nearly transparent wings above its beak.

Back on the ground the heron stares into the water with statuesque stillness. Then it dives below the surface to bring up a morsel.

It clambers back onto the rock with the aid of wet wings.

Its victim is the nymph of a large dragonfly species, probably one of the Common green darners that frequent the pond.

 

 

The heron flips its meal around head first for easier swallowing.

The hunter has a complicated beauty precisely adapted to its purposes.

Pond Life 1 - The Resident Warbler



Male Common Yellowthroat

 Meet the thumb-sized proprietor of the wooded wetland, with his brassy voice and dashing mask.

Female Common Yellowthroat

He has livened up the glade since early May. He arrived from Central America a week ahead of prospective brides.

While most of the migrating warbler species search for food in the treetops and move on north, Yellowthroats settle down low in dense thickets across Massachusetts. This one advertises his plenteous domain, "Wichety, wichety, wichety."

Water's-edge vegetation supports abundant meals for an agile hunter of bugs, spiders, and grubs.

Lily pads are there for browsing on occasional forages out of the brushy tangles.

The quick-flitting understory life of the Yellowthroat resembles a House wren more than a warbler, and their out-sized vocalizations are strikingly similar.

The Yellowthroat pair have a nest close by. They tend their fledglings by taking carefully disguised routes to the nest. At summer's end all will fly out of the world of the pond on a southward migration of a thousand miles or two.