Island Science

Flying Dragons

• by Dr. Sarah D. Oktay, Managing Director UMass Boston Nantucket Field Station •

dragonflyWhat is strong, a skilled hunter, ephemeral, eats mosquitoes and feeds a wide variety of birds, fish, and frogs? Give up? It is the beautiful dragonfly, currently gracing Nantucket ponds and wetlands this summer. Some of the best places to see these beauties are Hummock , Tom Nevers. Miacomet, Gibbs, and Sesachacha ponds. The Nantucket Field Station pond is home to thousands of these elegant fliers.

A dragonfly is an insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera (from Greek “anisos for “uneven” and “pteros meaning “wings”, because the hindwing is broader than the forewing). It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body. Dragonflies possess six legs (like any other insect), but most of them cannot walk well. Dragonflies are among the fastest flying insects in the world. Adult dragonflies do not bite or sting humans, though nymphs are capable of delivering a painful but harmless bite.

Dragonflies are important predators that eat mosquitoes, and other small insects like flies, bees, ants, wasps, and very rarely butterflies. Some 5680 different species of dragonflies are known in the world today. Though dragonflies are predators, they themselves are subject to predation by birds, lizards, frogs, spiders, fish, water bugs, and even other large dragonflies (from http://en.wikipedia.org/wiki/Dragonfly retrieved August 18th, 2013.) Dragonflies can range in size from 7/10 of an inch to several inches wide. The Megaloprepus coerulatus damselfly of Central America has a wingspan up to 19 cm. The bulkiest known dragonfly is Petalura ingentissima from Australia, with a wingspan up to 16 cm. The largest dragonfly fossil (Meganeura) had a wingspan of nearly three feet. That makes it the largest flying insect in known history. Scientists think that super high oxygen levels in the atmosphere (up to 30%) allowed dragonflies to grow to the size of seagulls.

I lived and went to school (TAMUG) in Galveston, Texas (home of the fightin’ mosquitoes!) for ten years. The sky would fill periodically with huge swarms of dragonflies as their populations boomed in response to the abundant mosquito hatches. You have never seen humans cheer on the arrival of a swarm of insects with greater enthusiasm than mosquito weary half drained people of Galveston. I swear I heard Wagner’s “Ride of the Valkyries” in my head each time I saw them. These swarms were larger enough that they caused you to drive a little slower, a bit reminiscent of the huge swarms of sky darkening (and grill clogging) “love bugs” or Plecia nearctica.

Dragonflies are usually found near water such as marshes wetlands ponds and streams because the first portion of their lives as larvae or nymphs is an aquatic one. Both dragonflies and damselflies are found around ponds and wet areas. The primary difference between the two is that damselflies tend to be smaller and more slender (although not always) and they hold their wings over their back when at rest in line with their bodies while dragonflies hold their wings perpendicular to their bodies.

An excellent blog that I receive almost every week written by Matthew Wills  (http://matthewwills.com/2013/07/15/weekend-dragonflies/ retrieved August 18th, 2013) clued me into the bizarre and acrobatic world of dragonfly procreation. Matt’s excellent pictures of dragonflies and other denizens of the natural world around Brooklyn lead me on to an article in National Geographic entitled “Dragonflies Strange Love”. Apparently dragonflies can be quite violent in the “romance” department and will punch, bite, grab and shake their mates. You’ve more than likely witnessed linked dragonflies flying together or alite on a leaf, but I doubt you are aware of the bloodshed that led to that “tender” moment. Philip Corbet, a biologist from Cornwall in England describes some of the many down and dirty tactics males use to ambush females including while they are laying eggs or newly emerged from a pond.

“Anyone who has watched dragonflies mating in the bright air has seen a wonder of evolution, Corbet says. Odonates, as they’re called, or “toothed ones,” have been around for more than 300 million years, which has given them time to figure all the angles on sex. Judged by their longevity and diversity (6,000 species) and the scope of their distribution (every continent except Antarctica), they’re one of nature’s great reproductive success stories.

Male dragonflies sport two sets of sex organs, the prerequisite equipment for a mating system that is unique in the insect world. Before he copulates, a male dragonfly must in essence self-inseminate, moving his sperm from the testes to the storage pouch and into the penis. Here comes the tricky part. He must grip a female by the head or thorax and hold her in the tandem position, with claspers at the tip of his abdomen that fit neatly, like a lock and key, with a special plate on her thorax or behind her eyes.” http://ngm.nationalgeographic.com/print/2006/04/dragonfly-mating/ackerman-text  retrieved August 18th, 2013.

A familiar and specific to dragonflies “wheel formation” occurs after the aerial hokey pokey for many dragonfly species once they have become attached. In order to become the winning father, the dragonfly needs to be the last one in line as it were (trying to keep this as a family column) so they will chase off any other males until the female lays her eggs. The male will also remove with scrapers or bristled lobes attached to their sexual organs any evidence of a male that may have beat him to the punch.  In case you are keeping track, damselflies normally tend to attach themselves around the neck instead of behind the eyes, but either way that is pretty yogic or tantric. Entomologists (people who study insects) have to be familiar with a dragonfly’s naughty bits because that is the best way to identify different species.  A male dragonfly must also be able to pick out his mate from a crowd of other flying insects and he does that by observing her flight style, her colors and patterns, and her size.

After all this hullaballoo, the female lays her eggs in the water often on a lily pad or other submerged plant or near enough to a pond where she knows it will be covered by water. Many people believe dragonflies are extremely short lived but that is not true. The life cycle of a dragonfly from egg to the death of the adult is about six months at least, sometimes much longer. Most dragonflies don’t die of old age but are caught by predators.  Their life span is dominated by their underwater aquatic life existing typically only for a few months as actual adult dragonflies. After the female has laid her eggs, they incubate for a few days, maybe a week or two, and then hatch into naiads also called nymphs. You may recall that naiad is the ancient Greek name for mythological water nymphs, Most of a dragonfly’s life is spent in the naiad form, beneath the water’s surface, using extendable jaws to catch other invertebrates (often mosquito larvae) or even vertebrates such as tadpoles and fish. In the nymphal form while they are scooting around eating other insect larvae including mosquito larvae, nymphs breathe through gills in their rectum (nice!), and can rapidly propel themselves by suddenly expelling water through the anus (even better- insert joke about your human mate here). They will live as naiads for up to four years, molting their skin between 8 to 17 times depending on the species.

In the April 2 2013 issue of the New York Times we learn that dragonflies are one of the most effective and vicious hunters in the animal world, beating lions and great white sharks in efficiency and kill ratios with up to 95% accuracy in their ability to hone in and capture prey during flight.

“Dragonflies are magnificent aerialists, able to hover, dive, fly backward and upside down, pivot 360 degrees with three tiny wing beats, and reach speeds of 30 miles per hour, lightning for an arthropod. In many insects, the wings are simple extensions of the thoracic box and are moved largely as a unit, by flexing the entire thorax. In the dragonfly, the four transparent, ultra flexible wings are attached to the thorax by separate muscles and can each be maneuvered independently, lending the insect an extraordinary range of flight options………Dragonflies are true visionaries. Their eyes are the largest and possibly the keenest in the insect world, a pair of giant spheres each built of some 30,000 pixel-like facets that together take up pretty much the entire head……Their other senses get short shrift. Dragonflies can’t really hear, and with their stubby little antennas they’re not much for smelling or pheromonal flirtations.” http://www.nytimes.com/2013/04/02/science/dragonflies-natures-deadly-drone-but-prettier.html?pagewanted=all&_r=0 retrieved August 18, 2013. I highly recommend reading the entire article to learn more about their abilities to target and visualize the movements and location of their prey.

The Field Station’s virtual and physical nature trail has a kiosk with information on dragonflies typically seen around our pond. Of the 30 species of dragonflies and damselflies recorded on Nantucket, 18 have been seen at the Field Station. The large, orange, coastal dragonfly known as Needham’s skimmer (Libellula needhami) can occasionally be seen resting among the shoreline vegetation, while the familiar bluet damselfly (Enallagma civile) prefers to stay low, perching on emergent rushes out over the open water. The Eastern Forktail (Ischnura verticalis) is another beautiful damselfly. The male is green with a light blue “tail light”, while the female is orange http://www.cs.umb.edu/nantucket/stop9.html retrieved August 18th 2013.

Many people know that big beautiful butterflies like monarchs migrate, but did you know there are several species of dragonflies that migrate? Frank Nicoletti, a professional hawk counter and bird-bander, noticed that kestrel (small raptors which are talented dragonfly hunters) migrations were linked with the migratory patterns of green darners (http://www.learner.org/jnorth/tm/fall/DragonflyMigration.html retrieved August 18th, 2013). Like birds, dragonflies often migrate north in early spring to breed and then migrate south from late summer to mid-fall to escape the cold. They seem to navigate south by using natural landscapes such as mountains, seacoasts and large rivers. Large migrations have been observed in the warmer climates, such as the Gulf of Mexico and other sub-tropic and tropic climates. Dragonflies can also migrate either as individuals or as mini swarms travelling short or long distances.

I spent an inordinate amount of time trying to take a picture at Tom Nevers Pond of a Common Whitetail or Long-tailed Skimmer dragonfly (Plathemis lydia) which is a common dragonfly found across much of North America, with a striking and unusual appearance. The male’s chunky white body (about 5 cm long), combined with the brownish-black bands on its otherwise translucent wings, give it a checkered look. I have included an image by Bruce Marlin taken in Illinois in 2003 (see above) instead of one of my 20 blurry photos.

I hope before summer has passed that you get out to one of our many ponds and simply sit for a spell and watch for these lovely and aerobatic flyers as they dart around and hunt mosquitoes.

Charles Willison Johnson’s “A List of Insect fauna” including James H. Emerton’s List of Spiders was published in 1930 by the Maria Mitchell Association and lists 24 species of dragonflies and damselflies for Nantucket ( from http://ag.udel.edu/enwc/research/delphacid/documents/Johnson1930aHomopteraonly.pdf retrieved August 18th, 2013. That is not very many compared to Texas’ several hundred species which makes Texas the primary state for dragonfly observers.

Another useful text that gives a list of “The Dragon and Damsel-Flies (Odonata) of Nantucket, Mass. “ by R. H. Howe, Jr. was published in 1917 the Annual Report of the Maria Mitchell Association, (vol. 16, pp.1.1-1.3 http://adsabs.harvard.edu/full/1918MMAAR..16….1H retrieved August 19th 2013). Dr. Howe found 21 species of dragonflies and damselflies.

Learn more about dragonfly migrations from http://www.migratorydragonflypartnership.org/uploads/_ROOT/File/Migration%20Review%20JICO%202012.pdf.