The Dragonflies are Coming!
By David Herlocker, Marin County Parks Naturalist
It is hard to spend even a few minutes near the shore of a pond or stream without being aware of the presence of dragonflies.
Marin County is home to an amazing array of different dragonflies, and there are many places where you can see ten or more species in an afternoon. If you would like to learn more about these insects, the Marin County Parks Naturalist Program is offering a lecture on this topic on Wednesday June 20 from 7:30 to 9pm at the Marin Humane Society. We will also host a walk to study dragonflies in the field on July 5 at Stafford Lake from 9am to 12 noon.
These large, often brightly colored insects are easily recognized by most people. In spite of the fact that dragonflies are among the most primitive flying creatures aloft today, they are also among the most elegant, maneuverable, and downright acrobatic fliers that have ever lived. While these eye-catching aerobatics and gaudy good looks are enough to capture our attention, knowing the life stories of these insects should make them even more interesting.
Ponds are not the only places to see dragonflies, in fact adult females usually spend more of their time away from water, sailing over meadows and forests catching flying insects. When they have eaten a sufficient amount to nourish a batch of eggs, the females seek out a suitable fresh water habitat for egg laying. Some species prefer dense stands of shoreline vegetation, others look for floating mats of algae, while some opt for rapidly flowing streams. Adult males usually hang out near the water’s edge, they stake out territories where females are likely to want to lay eggs, and patrol the area throughout the day. They chase off rival males, and pounce on females when they arrive. After mating, the male will guard the female, either by holding onto her, or by hovering above her while she lays eggs.
When the eggs hatch, a tiny insect called a nymph (or naiad) emerges into the water. Dragonfly nymphs are curious looking creatures; some are streamlined and torpedo like, others resemble spiders with long legs and squat, boxlike bodies. Immediately after hatching, they are ready to begin eating. All dragonfly nymphs are predators. They employ a sit-and-wait technique to capture insects and other small animals that pass their way. Nymphs have a unique system of prey capture. They have an extensible lower lip that sits folded beneath their head while they are at rest. When they detect prey, the lip can be thrust forward with lightning speed. At the end of the lip is a trap-like device with two hooked teeth that impale the prey. The lip is then withdrawn, pulling the prey back to the mouth where the mandibles tear the food into smaller pieces which are then swallowed. The nymph stage may last a month or even several years, but eventually, the nymph climbs out of the water and sheds its skin for a final molt. The skin splits down the middle of the back, and the pale, soft bodied adult wriggles free. At first it resembles a nymph, but slowly the wings are inflated, the body is extended, and within hours, the adult assumes its final shape. During emergence, they are extremely delicate and vulnerable, it is not uncommon to see a red-winged blackbird moving methodically along the edge of the water, systematically plucking off emerging dragonflies one after another. Once the wings are fully formed, most dragonflies will fly away from the water to rest in a sheltered place while their skeleton and wings become hard.
Adult dragonflies feed while in flight. They use their large eyes to spot smaller insects, and they dart toward their prey with a sudden burst of speed. Prey is usually captured with the legs, each of which is equipped with several rows of sharp spines. The legs hold the prey basket-like, and push it forward to the mouth where it is dismembered and swallowed. If you watch closely, you can see the legs and wings of larger prey items being casually dropped as the meal is consumed. The adult phase of life is seldom as long as the underwater nymphal stage, most dragonflies only live a few weeks after emerging.
For more information on these programs contact David Herlocker at: email@example.com, or call (415) 893 – 9508