Dragonflies are large ferocious predators in the insect world. However, if you are lucky enough to have one land on you while sunning on the beach or dock, don’t be afraid, it won’t bite or sting you. More likely, it is busily eating a fly that was about to bite you. Take the time to examine the dragonfly’s features and just enjoy it. When seen through binoculars or in a close-up photograph they rival birds and butterflies in their patterns and colours. In fact, more people are becoming dragonfly watchers, a pastime increasingly popular since the publication of several new field guides for their identification. The dragonflies and damselflies of Algonquin Park, published just last fall, covers all dragonflies in the Parry Sound area. As with butterflies, a dragonfly, basking in the sun, will occasionally allow approach to within inches for close-up photos. So you don’t have to catch them in a net to enjoy them.
Dragonflies have three main body parts: the head with large compound eyes, the strong central body part – the thorax – between the head and the tail to which the wings and legs are attached; and the long trailing abdomen or tail which holds the reproductive parts. The wings are not folded but held out horizontally when at rest. Strong muscles in the thorax power the stiff rapid wing beat allowing powerful flight and instant change of direction. They are the insect masters of the sky.
Dragonflies are cold blooded and only fly on warm sunny days. They usually spend some time in the late morning sitting in the sun to warm up and this is a good time to get a close look at them. In the adult flying stage they feed voraciously on flying insects such as mosquitoes, flies, bees, and even other dragonflies. Once, while walking through the woods surrounded by a swarm of deer flies, I could hear the occasional wing noise of a dragonfly very close to my head as it snatched the flies in mid flight or caught them as they sat on my hat. Another time, as I was very slowly moving closer to a beautiful butterfly, it suddenly disappeared in a flash. It didn’t just take to flight but had been snatched by a dragonfly, a Black-shouldered Spiny-Leg, which I spotted much higher up in the shrub busily consuming the butterfly I had hoped to photograph. Dragonflies often stray far from the water in search of food and can be seen patrolling edges of openings in the woods or along roadsides. Males usually patrol an area, sometimes quite small, cruising back and forth, continuously looking for prey, or for a mate. In late afternoon as the sun gets lower in the sky, they find a sunny edge and sit on an exposed twig or tall grass stem to catch the last rays. This is another good time to get close looks at them.
Mating is a complex process. The male has specially adapted claspers at the end of the abdomen which he uses to grab and hold a female by the back of her head. At this point they are “in tandem”. The female then curls her abdomen until the tip attaches to the male just under the front of his abdomen to receive his sperm. In this position they are said to be “in wheel”. While in tandem or in wheel they may be perched or constantly fly from place to place.
When the fertilization is complete, the males of some species continue to hold the female in tandem while she deposits her eggs into ponds or the edges of lakes. Some females drop their eggs into the water like little bombs, which then sink to the bottom. Others have a spike-like ovipositor at the end of the abdomen which they use to pierce the stems of aquatic plants so they can lay their eggs in the stem. Dragonflies have been known to mistake human legs for plant stems, harmlessly jabbing at them as they attempt to lay eggs. They also sometimes mistake shiny surfaces such as vehicle hoods for smooth water surfaces and drop eggs on these.
Under the water the eggs hatch into the next stage of the life cycle, the dragonfly nymph. One of the more voracious predators in the aquatic food chain, the dragonfly nymph has specially adapted arm-like “lips” that reach out with lightening speed to grab prey as large as tadpoles. They eat various aquatic insects including mosquito larvae. If there are no fish present to eat them, they may be a top predator in the aquatic food web. Most of a dragonfly’s life is spent in the nymph stage under the water at the bottom of a pond. With some larger species, the nymph lives several years, surviving through winters. As it grows it sheds its outer skin several times. There is no pupa stage in the dragonfly life cycle as there is with butterflies.
When the time arrives for the adult to emerge, the nymph crawls out of the water on a stem or the side of a dock, the nymph’s case splits open just behind the head, and the dragonfly crawls out. The wings then unfold as fluid from the body is pumped through the veins. They are very vulnerable to predators at this time as it may take an hour or more before the wings become strong and dry allowing the insect to fly. The newly emerged juvenile is very pale and takes a week or more to mature and develop the bright colours of the adult. During the month that most adults live they go about feeding, defending territories, searching for mates, and reproducing. The nymph’s empty skin, called the exuvia, remains attached to the stem or dock. Empty nymph skins are easily found and can even be used by professionals to identify the species and sex of the dragonfly that emerged from them.
One of the most awesome dragonflies is the Dragonhunter. Its name refers to its main prey, other dragonflies, some as large as the Dragonhunter itself. Powerfully built with an extra large thorax and strong legs, it is the T-rex of the dragonfly world, chasing down and snatching its dragonfly prey in mid-air. It is fairly common in the Parry Sound area and easy to recognize in flight because the tip of its abdomen is curved downward rather than held straight out like other dragonflies. The curve of the abdomen can even be seen sometimes in a perched Dragonhunter, Look for the Dragonhunter cruising along the shoreline. It sometimes lands on docks.
The Green Darner is a large dragonfly widespread throughout North America as far north as southern Canada. It is easily recognized by its all green thorax and bluish abdomen held straight out as it flies. It rests like all darners with its body in a vertical position clinging to a strong grass blade or slender twig close to the ground. It is a bit like the Monarch butterfly in that swarms of them migrate south in the fall.
Large numbers of Green Darners have been observed migrating south at the same time as American Kestrels, small falcons, which are thought to feed on the Green Darners. It is not known where the migration ends but it is thought that in the south the darners mate, lay eggs, and die. The nymphs hatch and then grow to full size during the winter.
The next generation of adults emerges in the spring and migrates north. Their life cycle is not that well known and it could be that some Green Darners do not migrate but rather overwinter in the north as nymphs. This is consistent with larger dragonflies in the north that spend several years as nymphs, the time needed to mature, before emerging as adults. Much is still to be learned about dragonfly migration. The Green Darner is found in a variety of aquatic habitats and sometimes far from water in fields and along roadsides.
The Calico Pennant is a medium to small sized beautiful dragonfly. It is also very common around Parry Sound. Usually they can be found in dry grassy areas sitting on the tops of grass stems. The male’s deep red pattern is replaced by a rich yellow in the female.
The large Twelve-spotted Skimmer has an all-white abdomen and striking black and white wing pattern. Its name refers to the twelve black areas on the wings. It is often found around shallow ponds or ditches with gravel or rocks.
There are about 56 species of dragonflies just in the Parry Sound area. Take the time to look at them and you too may discover another wonder of nature right on your doorstep. Who knows, you might become interested in their smaller cousins, the damselflies. But that’s for another column.
Dragonflies winged marvels
Date: Feb 05, 2010
Dragonhunter. The powerful T-rex of the dragonfly world.
User Comments
