by: Paul-Michael Brunelle
SPRING 1992
We hold few insects in high esteem. Butterflies are generally enjoyed, and beetles do not usually terrify; but generally "bugs" disquiet and annoy us. From our perspective some do so for good reason. There are insects that see us as a travel ling canteen, or that will sting or bite if disturbed (though few seriously).
Still, most insect groups (99 per cent) do not deserve our ill opinion. One of these is the order Odonata, or dragonflies (suborder Anisoptera) and damselflies (Zygoptera). In spite of common names like Snake Doctor and Devil's Darning Needle these insects are harmless and indeed beneficial to us. They eat many of the pests we despise such as mosquitos and blackflies, and they do not "sew our lips together," bite or sting us. Their nymphs feed the fish and waterfowl we delight in. And, depending on the species, they are quite beautiful in an innocent or sinister way.
The dragonflies (1 will use this name for both dragon- and damselflies in general discussion) have come down to us almost unchanged (except in size) from 300 million years ago. Fossils of one ancient species are about 24 inches (60 cm) long, easily twice as large as any insect ever discovered and larger than most contemporary birds. The largest of these insects today is 8 inches (20 cm) long and the largest in Nova Scotia is 4 inches (10 cm).
Adult dragonflies (Anisoptera) are unusually large insects (1.5-4 inches, 4-10 cm long) with four large wings held horizontally to the body.
They are brightly coloured with blues, greens, yellows and reds, and some species have black, white and orange markings on the wings. They have huge compound eyes, which are hexagonally faceted, and their eyesight is very acute for an insect. They are exclusively carnivorous, devouring great numbers of insects daily. They are strong fliers and extremely agile in the air. For example, the Swift River Cruiser (Macromia illinoiensis) flies at over 50 miles per hour and can dodge a net with contemptuous ease-very annoying to try to collect. My wife Meredith once spent an afternoon watching me try to catch one particularly aggravating specimen. I'm not sure which of us she was rooting for.
Adult damselflies (Zygoptera) are smaller in temperate regions; our largest is less than 2 inches (5 cm) in length. Their flight is less strong and in some species (particularly the "Jewelwings" or Calopteryx found near rivers), the flight is fluttery like meadow butterflies. They perch with the wings held together or at a slight angle apart above the body.
Their coloration is also intense and often iridescent. One species in the province, Argiafumipennis violacea, has a male of the most beautiful violet colour; and the male Calopteryx spp. winks like a neon green mirror about our rivers and streams, made even more striking by the ebony markings of the wings.
The Odonates are ubiquitous in temperate and tropical regions the world over basically any freshwater body that does not freeze to the bottom in winter and that is not polluted will be found to have a dragonfly population. There are about 100 species recorded from Nova Scotia, and 1 suspect more will be found if interest grows.
The order has few species by insect standards, only 5-6,000 world-wide compared to the 300,000 species of beetles, so entomologists consider it a small and well known group. There are, however, still many things to learn.
Dragonflies and damselflies begin as eggs deposited in or near the water. After hatching the aquatic "nymphs" are ferocious predators upon aquatic life. They use a unique structure called the "labium" resembling a single arm folded under the head with sharp hooks at the end. It is unfolded to strike in what may be the fastest physical movement in the animal kingdom.
Damselfly nymphs have three featherlike gills on the end of the abdomen and are slim. Dragonfly nymphs have instead small spike-like appendages and are generally heavier.
Nymphs grow through stages separated by molts, when the exoskeleton (hard skin) is cast off and the nymph grows in size before its next skin hardens. After a number of molts over the course of one or more years the insect "emerges." This is a spectacular transformation (ironically called ',simple metamorphosis"), which 1 feel rivals in wonder the "complex metamorphosis" of the butterflies. The dragonfly goes from aquatic nymph to aerial adult in a matter of hours. Left behind is the cast-off skin, a hollow shell retaining the external characteristics of the nymph. This cast-off skin is often useful in identification.
The newly emerged adult is soft-bodied and less striking in coloration than when fully mature. Females generally leave the water for the surrounding forest in order to escape the pressing attentions of the males until they are sexually ready; males stay near water and begin the territorial behaviour, peaking with the return of the females.
The dragonflies have elaborate courtship rituals, culminating in breeding in the "wheel position." Another unique aspect of the group, one that is difficult to explain. In order to achieve fertilization in this position, the male has evolved "accessory genitalia" under the second abdominal segment, which serve to transfer sperm from his primary genitals (at the end of the abdomen) to hers. What advantage this complex arrangement conveys is subject to discussion, but the pair can fly during copulation (difficult in the conventional insect position). Presumably in ecologies with heavy predation this has given them an edge.
The female lays her eggs either by dropping them in the water or by inserting them in plant tissues by means of an "ovipositor." Depending on the species the male may abandon her after fertilization, remain to guard her, or travel with her in the "tandem" or towing position, clasping her behind the head with the tweezer-like claspers on his abdomen. 1 have observed damselfly females laying eggs in underwater plants to a depth of 20 inches (50 cm) for up to half an hour, sometimes with the male still in tandem.
Following breeding the adults live a short time, dying with the first frosts or falling prey to other dragonflies, birds, spiders or frogs.
An interest in dragonflies can prove rewarding and satisfying, and has the advantage of being considered only mildly eccentric. It will get you out in the wilds where you'll see many new things, particularly since you are looking for such small animals. And it will contribute to your appreciation of the complexities of the natural world. Once you have such an appreciation it becomes much less difficult to take those steps that we must to preserve our environment.