August 23, 2021
When I left work last week, I was greeted by a swarm of Dragonflies. While I have often seen Dragonflies around the lakes I fish, my work is at least a half mile (800 meters) from the nearest water, and that is a stream rather than the placid water of a lake. There had to be at least 30 dragon flies circling in a massive mating dance. While it was intriguing to watch them swarm, I wondered why they were there, and where they would ultimately lay their eggs. These are questions the types of questions inquiring minds need to know.
When I looked online, I found that dragonflies are an insect belonging to the order Odonata, infraorder Anisoptera (from Greek “unequal” and “wing”, because the hindwing is broader than the forewing). Adult dragonflies have large, multifaceted eyes, two pairs of strong, transparent wings, and an elongated body. Many dragonflies have brilliant iridescent or metallic colors making them conspicuous in flight. Dragonflies are predators, both in their aquatic larval (nymph) stage and as adults. In some species, the nymph stage lasts up to five years, and the adult stage may be ten weeks. Most species have an adult lifespan in the order of five weeks or less, and some only survive for a few days. They are fast, agile fliers, sometimes migrating across oceans, and often live near water. There is also a reservoir located two miles north of my office. That answers the first question, as the swarm could have moved in from anywhere and over long distances.
Dragonflies can be mistaken for the related group, damselflies (Zygoptera), which are similar in structure, although lighter built. About 3,000 extant species of true dragonflies are known. Dragonflies have complex reproduction, involving indirect insemination and delayed fertilization. During mating, the male grasps the female at the back of the head, and the female curls her abdomen under her body to the front of the male’s abdomen, forming a “heart” or “wheel” posture. The female later deposits eggs one at a time as she dips up and down into water. That answers the second question, as the dragonflies could use either of the two water resources to lay eggs.
Thoughts: Habitat degradation has reduced dragonflies across the world. One example is that over 60% of Japan’s wetlands were lost in the 20th century. The dragonflies now depend largely on rice fields, ponds, and creeks. Dragonflies feed on pest insects in rice and serve as a natural pest control. Another problem is the Dragonflies are attracted to shiny surfaces that produce polarization which they mistake for water. They have been known to aggregate close to polished gravestones, solar panels, automobiles (my Jeep?), and similar structures where they attempt to lay eggs. We are increasingly shown that the conspicuous consumption of resources by humans not only degrade the land and water but cause the extinction of marginal species. Ecosystems are designed to work in cooperation. Humans must not ignore this fact. Follow the science. Change is coming and it starts with you.