June 24, 2014 Dragonflies: Ancient Aerial Predators
Dragonflies and their ancestors have survived on Earth for over 300 million years. Fossils show that ancient dragonflies had wing-spans of over 28 inches (70 centimeters). Today there are more than 80 different species that occur throughout the West.
The name dragonfly comes from the Greek word for tooth, likely because of their very impressive chewing mouthparts. Dragonflies are harmless to humans. They have an unwarranted reputation that has instilled fear into people.
There are about 5,500 different species of dragonflies worldwide. Some are as colorful as birds and butterflies with iridescent, metallic green and crimsons.
They all possess a similar design of a head, a thorax (sturdy midsection) and a long abdomen. Their head contains two compound eyes with as many as 30,000 lenses in each eye. And two inconspicuous antennae which scientists believe act as a speedometer. Dragonflies can reach a top end speed of 60 kilometers per hour. They have two pairs of large veined-wings about equal length attached to the thorax. The abdomen is long and narrow with 10-segments. Their six legs are not used for walking instead they are important for perching, scooping up and handling prey and the front two legs are used for grooming the eyes and face.
This basic design has produced such a finely tuned aerial predator with superb vision and unmatched aerial agility, that it has undergone no significant modifications for millions of years.
Dragonflies are like us because their eyes are the primary means of assessing the environment.
They live around most types of water: lake shores, streams, springs or peatlands. They predominate near standing water spending their entire youth as larvae in water. They are high-level predators with huge hinged labiums (lips) with the lower one armed by pincers that grasp prey. Small fish, aquatic insects, crustaceans and tad-poles are all preyed upon. Dragonflies zip through the water by blowing water out through their anus.
They must eat a lot because they shed their skin about 13 times before reaching adulthood. Most species over-winter as larvae and emerge the following spring or summer, metamorphosize, shedding their hard outer shell as it splits along the back and within a half an hour they are able to perform aerial maneuvers including flying upside down.
Adult dragonflies are voracious predators. They can eat just about any animal they can catch and chew including other dragonflies. There are two types of aerial feeding. Hawkers are in constant pursuit of flying insects. Salliers, on the other hand, dart from a perch, capture prey and return to their perch.
Dragonflies avoid predators like birds, bats, flies, wasps and even other dragonflies by agile maneuvering. Bright blue colours of some species, that could attract predators, fade to gray at cooler temperatures when mobility is reduced.
Females find mates near water usually in the late morning or early afternoon. Courtship is rare. Males pounce females attaching their abdominal appendage to the raer of the female head or thorax. The male transfers his sperm from near the tip of the abdomen to a storage area in his secondary genitalia. The female bends her abdomen forward to align her reproduction structure under her eighth abdominal segment in line with the males secondary genitalia.
When they lock together in copulation it is called a wheel and sometimes it can resemble the shape of a heart. It can last for a few moments or hours. As the males secondary genitalia has a special sucking pump designed to remove other males sperm. Females often mate with other males.
Once copulation is complete the male will hover overtop of the female to guard against other possible male suitors whilst she lays her eggs in the water.
Dragonflies have stood the test of time. They are awesome critters who depend upon healthy aquatic habitats that grace the exquisite West.
Earth Dr Reese Halter is an award-winning broadcaster and distinguished conservation biologist. His latest book with Chris Maser is Life, The Wonder of it All
Text © by Dr Reese Halter 2014. All rights reserved.