Wednesday, June 24, 2009

Early Season Dragons

12-Spotted Skimmer (male)

Dragonflies have become a very common sight over ponds, streams, wetlands, and fields over the past few weeks. Many people are familiar with these insects as a group but are less likely to recognize one individual species from another.

Watching and identifying dragonflies is similar to learning to identify birds. Most of them have similar shapes and sizes with small details of appearance or behavior that set species apart from one another. Even males and females of some species are different in appearance.

One of the most remarkable facets of these incredible insects is their unique lifestyle. Similar to the way a frog begins its life underwater, so it is for the dragonfly. All during the summer, adult dragonflies can be observed mating above and laying eggs in many of the area's bodies of water. The eggs eventually hatch and the dragonfly lives the first half of its life as a nymph underwater.

Dragonfly nymph

The nymphs breathe oxygen from the water through a set of gills located inside the abdomen, or rear portion, of its body. During this stage of its life, the nymph is interested in one thing: Food. Dragonfly nymphs are predators and spend much of their time eating other members of the pond community, usually other insects, worms, snails, tadpoles, and small fish. Of course they're not immune to becoming a meal for one of the pond's fish, frogs, turtles or birds. The nymphs will continue to eat and grow, shedding their exoskeletons many times, for as little as a few months or as long as a few years. Once the time is right, the nymphs will crawl from the water to a sheltered location and shed their nymphal exoskeleton one last time.

Dragonfly nymph exoskeleton

Once the dragonfly emerges from its nymphal exoskeleton, the body and wings unfurl, the blood begins to pump, and the new exoskeleton must harden before the adult dragonfly can effectively take to the sky. Once it becomes airborne, the dragonfly patrols the skies for all manner of potential prey. Mostly opportunistic, they will take flies, midges, butterflies, damselflies, and other dragonflies. They themselves often become prey for birds, frogs, fish, and spiders. The life cycle begins again when the newly emerged adults mate and lay eggs.

So here are a few of the dragonfly species seen recently around the sanctuary:

Common Whitetail (female)

The Common Whitetail is one of a number of species of dragonflies in which the mature males and females look quite different. The females have brown bodies with yellow-ish markings on the sides of the thorax and abdomen and and black patches on the base, middle, and tips of all four wings (see below).

Common Whitetail (female)

Male Common Whitetails are very similar to females as immature adults (see photo below). The biggest difference is the pattern of black on the wings. Males have only the large patches on the middle of each wing (hidden by my thumbs in the photo) and small bars at the base. As they age, the male's abdomen will turn a chalky white color.

Common Whitetail (male)

Common Baskettail

The Common Baskettail is pictured above and below. This species is difficult to identify due to it's rapid and erratic flight. They often fly in swarms over fields, forest clearings, and other similarly open areas. So in this instance, the dragonfly's behavior, not it's appearance, is one of the best clues to it's identification. In this case, an insect net for capturing a specimen was especially helpful for complete identification. This one happened to be a female as evidenced by the collection of eggs at the tip of its abdomen in the photo below.

Common Baskettail (female) with eggs

The first dragonfly at the top of this post is the 12-Spotted Skimmer. The male is different from the female mostly due to the white patches in between the black patches on each wing. Female 12-Spotted Skimmers and female Common Whitetails are very similar except for the shape of the yellow-ish markings on the two species abdomens. Perching behavior is helpful for identifying these two similar species: 12-Spotted Skimmers tend to perch horizontally in vegetation and Common Whitetails tend to perch horizontally on logs, rocks or the ground.

Next time you see a dragonfly, take a closer look. You may notice the next one doesn't actually look the same as the last one. There are many species in our area and all are unique and beautiful if we take a moment to look a little closer

-Adam Zorn, Naturalist

1 comment:

Gina said...

I love this! And the frog hiding in the fence too. And the story about the milk snake in the shed.

Great work, Adam.