ZOO-ology column: Dragonflies hunt mosquitoes
Sept. 4, 2011 at 4:04 a.m.
By Judie Farnsworth
Imagine stepping outside and finding a dragonfly with a two and a half-foot wingspan.
Fossils show that dragonflies of the late Paleozoic Era (300 million years ago) were that big. Except for size, they're pretty much the same - one of the most primitive living creatures on Earth.
They're fodder for some wild myths. One of the strangest is that they bring snakes back to life or follow them and stitch up any wounds.
Horse stinger is another name and myth. Dragonflies cannot sting. In fact, they are extremely beneficial. Among Native Americans, they are a sign of happiness, speed and purity.
A dragonfly starts life as a tiny egg deposited with others on aquatic plants or scattered in still water. The egg hatches into a dragon-like aquatic larva called a nymph that may live in the water for several years, its longest life stage. It breathes water through gills in its abdomen and can force the water out for jet-propelled movement.
It's a carnivore (meat eater) eating tadpoles, mosquito and other larva, tiny fish and worms. It will molt its skin several times while growing, then crawl from the water and up a plant stem for a final molt.
The now beautiful dragonfly has only a few weeks or months to live. It looks for a mate and hunts for food. It's an insect killing machine - sometimes called a mosquito hawk - and if you're a mosquito, you're its favorite meal. It can eat its own weight in food in about 30 minutes and may form a kind of basket with its legs to catch flying insects (gnats, termites, flies, even bees). It can out-maneuver them all.
Its wings are not jointed like butterfly wings and the parts operate independently. Flight can be up, down, left, right, forwards and even backwards. The dragonfly is one of the fastest insects in the world. Forward flight can be 100 body-lengths per second, and backwards, around three body-lengths per second. It can hover for about a minute. Speeds of 22-24 mph and a cruising speed of about 10 mph have been measured.
Enormous compound eyes with thousands of tiny lenses give a 360-degree field of vision. With this vision, incredible maneuverability and a voracious appetite for mosquitos, the dragonfly is one terrific exterminator.
It's a good indicator of unpolluted water, which is where it thrives. You may see chases among territorial males protecting clean habitats. Swarms may be related to weather fronts or a large food supply.
Dragonflies are part of the Odonata order (Greek for tooth) which also includes damselflies. Once thought to have teeth, we now know they have only hard mandibles that crush their prey.
Dragonfly and damselfly watching in the U.S.A. is a hobby similar to birding and butterflying. It's called Oding (from Odonata) and is popular in Texas where 225 species have been observed. Species number 450 in the U.S.A. and 5,000 worldwide.
There are differences between damselflies and dragonflies beginning with egg size, but for the casual observer, look at the wings. Damselflies hold their wings (resting) together or horizontal to their body. Most dragonflies (resting) hold their wings perpendicular to their body. Up close and personal, most dragonflies' huge eyes touch, damselfly eyes are apart.
Visit The Texas Zoo and look in the specimen drawers in the Animal Kingdom Building for Odonates and many other nifty things.
Judie Farnsworth is a longtime volunteer at the Texas Zoo specializing in educational programs.