Thursday, July 31, 2014

Our Remarkable Friends, the Dragonflies

Dear George,
One of my favorite places these days is the Oakleaf Trail at Miami Whitewater Forest.  There’s a path at the south edge of the trail that leads down to a bench at the edge of the pond, and it’s a peaceful place to contemplate nature and think about life’s quirkiness.  Fish nip at the water’s surface; frogs jump off the bank as people approach; ducks swim and feed; you might see a turtle if you’re lucky; and dragonflies flit here and there.   Watching the dragonflies takes me back to childhood on the Menominee River where they would hover around our rowboat and sometimes land and rest momentarily on our shoulders or arms.  It always made us nervous, but they never bit.  Dragonflies are certainly among the most majestic insects we encounter.  I realized how little I really know about them, so I asked Google a bunch of questions.  Here’s are some of the highlights.

Griffenflies (artist’s rendition)

How long have dragonflies inhabited the earth?  Longer than we can imagine.  Griffenflies, the giant precursors of today’s dragonflies, existed over 300 million years ago in the Carboniferous period.  With three-foot wingspans, they were the largest insects in history.  (1, 5) [note: #’s in parentheses refer to references at end]
How many different species of dragonflies are there?  There are about 5,900 different species of dragonflies in the world today, including 450 species in the U.S. and 114 in the state of Michigan alone.    Dragonflies inhabit all the world’s continents except Antartica. (4, 7, 12)

Where should you look for dragonflies?  They usually live around water because their larvae, known as “nymphs” or “naiads”, are aquatic. (12)

How big do dragonflies get?  Dragonflies range in size from one inch to six inches or more.  There are dragonflies in Costa Rica that have wingspans of 7.5 inches.  (6, 7)

What do dragonflies eat?  Dragonflies eat mosquitoes, as well as ants, bees, wasps, flies, and even an occasional butterfly.  A single dragonfly can eat several hundred mosquitoes a day.  For this reason alone, dragonflies are among humans’ best friends.  (11, 12)  

Dragonfly eyes

Can dragonflies see well?  Dragonflies have extraordinary vision.  Each of their compound eyes has up to 30,000 lenses, and they can see in many directions at once.  Their eyes make up almost their entire head.  They also can see a wider spectrum of colors than people can.  (1, 11) 

How fast do dragonflies fly?  Dragonflies are remarkable fliers.  They can move each of their four wings independently, and they can fly in any of six directions: up, down, forward, backward, and side to side.  Large dragonflies are among the fastest insects in the world.  They cruise at about 10 m.p.h., though they can reach speeds above 30 m.p.h.  One biologist reports measuring a dragonfly in the field flying at 60 m.p.h.  Scientists at Harvard have photographed dragonflies taking flight, catching their prey, and returning to a perch, all within one to 1.5 seconds.  Dragonfly flight is so extraordinary that engineers have envisioned designing flying robots patterned after them.  (11, 12)

Dragonflies in the wheel formation   

How do dragonflies mate?  First the male searches for an appropriate partner.  Since there are so many species, he has to identify a female of his own species from her flight style, coloring, patterns, and size.  While they’re both in flight, the male grabs the female around her thorax with his legs and clasps her by the neck.  As they’re flying in tandem, she bends her abdomen forward, and he connects his private parts to hers. This is known as the wheel formation because the couple forms a closed, heart-shaped circle.  Some pairs consummate mating in flight, while others retire to a nearby perch.  After mating, many males then guard their partners by chasing off and/or fighting with approaching males.  (2)

Do dragonflies lay eggs?  Females lay eggs in or near water, often on plants.  A single female may lay hundreds or even thousands of eggs at one time.  The eggs usually hatch in two to three weeks.  (3)

A dragonfly naiad

Do dragonflies fly as soon as they’re born?  No, definitely not.  In their initial larval stage, dragonfly naiads live underwater for two to three years.  This is the great majority of the dragonfly’s life span.  Naiads breathe through gills in their rectum and can propel themselves by expelling water from their rear ends.  They have extendable jaws that enable them to catch mosquito larvae and even tadpoles and minnows.  They shed their skins up to ten or fifteen times during their larval period.  (5, 12)

How long do adult dragonflies live?  After they’ve shed their final larval skin and emerged from the naiad stage, dragonflies can live for five to six months.  (12)

Do dragonflies migrate?  A number of dragonfly species migrate in response to cold weather.  Biologists have documented dragonflies called global skimmers making an 11,000 trip between India and Africa.  Migrating dragonflies can live longer than those who stay put.  (1)

Can dragonflies hurt human beings?  Adult dragonflies are harmless and don’t sting or bite people.  Naiads, on the other hand, can deliver painful stings to people (though the stings are harmless).  (6)

Birds eat dragonflies

Who are dragonflies’ predators?    It’s perilous to be a dragonfly -- they have a lot of enemies who like to eat them.  These include fish, birds, lizards, frogs, spiders, water bugs, and even larger dragonflies. (12)  Young, newly emerged dragonflies are particularly vulnerable, and it’s estimated that about 90% are eaten by birds and other predators.  (1)

Do people eat dragonflies?  Dragonflies are a food source in some parts of the world.  In Indonesia they are caught on poles and fried in oil as a delicacy.  (12)  

Where did dragonflies get their name?  Nobody knows for sure.  However, an author named Eden Sarot (1958) speculated that it came from an ancient Romanian folktale in which the Devil turned a beautiful horse into a giant insect.  Sarot's hunch is that, because "drac" is the Romanian word for dragon as well as Devil, "Devil's fly" eventually became transformed in the English language into "Dragon fly."  (13)

Red Dragonfly and Locust (Metropolitan Museum of Art) (8)

How are dragonflies viewed in various cultures?  In Japan dragonflies are symbols of courage, strength, and happiness.  In Europe they have been seen more often as sinister.  The Norwegian name for dragonflies means “eye-poker”; the Portugese name, “eye-snatcher”.  A folk belief in the southern U.S. is that dragonflies are “snake doctors” who follow snakes around and stitch them back together when they get injured.  (12)

All in all, dragonflies are astonishing.  Given all these facts, I don’t think I’ll ever view them quite the same.  Now I’m eager to get back to the pond at Miami Whitewater and see how many varieties I can spot.

SOURCES:  (1), “10 Fascinating Facts About Dragonflies”; (2), “How dragonflies mate”;  (3), “How many offsrpoimg do dragonflies produce at one time?”; (4), “Anisoptera”; 5), “Dragonfly”; (6), “The study of dragonflies”; (7), “Facts and myths about dragonflies”; (8), “Dragonfly dreams”; (9), “10 surprisingly brutal facts about dragonflies”; (10), “Dragonflies”;  (11), “14 fun facts about dragonflies”; (12), “Dragonfly”; (13), "How did dragonflies get their name"; (14), “Can humans eat dragon flies?”;  (15), “Green Darner Dragonfly”

G-mail Comments
-Phyllis S-S (8-20):  Dear Dave,,  This  was wonderful information. I used to adore watching dragonflies when I went fishing with my father.  Enjoyed the bibliography.  Phyllis
-Linda C (8-1): Thanks for all the interesting info. They are fascinating and always remind me of a fairy word…  Wish we could all get together sometime. Love Linda
-Gayle C-L (7-31):  David,  That was a cool read!.... Amazing, 5900 species. Here I thought there was only one!  Thank you for that!... Hope you get to see many of the varieties!  Love    G :)

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