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FIELD GUIDE

Dragonflies aren’t just pretty — they eat pesky bugs like mosquitoes

A male Common Whitetail dragonfly, photographed at the Ward Hill Reservation In Andover. Found throughout the state, Common Whitetails are one of the most abundant dragonflies in Massachusetts.DON LYMAN

While swimming with friends on a hot July afternoon, we noticed a large yellow dragonfly that kept zipping back and forth over the pool. Several times, the 3-inch-long insect flew just a foot or two above our heads, making us a bit nervous.

“People get concerned when they fly close by, but they’re probably just hawking [hunting] for mosquitoes,” said Matthew Burne, senior ecologist with the civil engineering company BSC Group, and coauthor, along with Blair Nikula and Jennifer L. Ryan, of “A Field Guide to the Dragonflies and Damselflies of Massachusetts.”

“If you pick them up, they can pinch you with their mandibles. But it’s hard to get them to do that.”

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In addition to eating mosquitoes, dragonflies feed on other flying insects, including black flies, said Burne. They’ll even eat smaller dragonflies, according to MassWildlife. Having suffered numerous bug bites this summer, anything that eats mosquitoes and black flies sounds good to me.

With a variety of colors including black, white, red, yellow, green, blue, and various combinations, along with their ability to hover in place and to fly in almost any direction, dragonflies are some of the most fascinating and colorful insects we see in Massachusetts.

These aerial hunters can be found in a variety of habitats, from forests and fields, to streams, lakes, swamps, as well as suburban lawns and gardens. My friend and colleague, Larry Kelts, biology professor emeritus at Merrimack College, said one species — Erythrodiplax berenice (aka, the seaside dragonlet) — even lives and breeds in local salt marshes and elsewhere along the East Coast.

Massachusetts dragonflies range in size from the diminutive 3/4-inch-long elfin skimmer to the common green darner, which can exceed 3 inches in length.

Mass Audubon lists 121 species of dragonflies in Massachusetts on its dragonflies and damselflies webpage.

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Dragonflies and damselflies ― which do not interbreed — are in the same order — Odonata — but these two suborders of insects look quite different.

Dragonflies are larger and bulkier than damselflies; hold their two sets of wings in a horizontal position while resting; have larger eyes that make up most of their head and give them a wide field of vision; and are powerful straight fliers, said Mass Audubon.

By contrast, damselflies are generally smaller than dragonflies; usually hold their wings together above their body when they’re at rest (except for spread-winged damselflies); have widely separated eyes that project to the side of their head; and are often weak, irregular fliers because they have smaller, more delicate wings and flight muscles than dragonflies.

Different species of dragonflies have different flight periods — when they metamorphose from their aquatic larval state into adults with wings and take to the air — said Burne, ranging from April to October. But summer is the peak time for dragonfly activity.

And whenever they’re flying, they’re probably breeding, said Burne.

Some dragonflies mate while flying, in what are called tandem flights, where the males and females fly through the air connected to each other, Burne explained, while others sit on plants while mating.

“Males have a specially evolved appendage, called the terminal appendage, at the end of their abdomen designed to hold the female at the back of the head while mating,” said Burne. “This is the mating wheel that you see [when the male and female are connected].”

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In some species of dragonflies, the male guards the female, holding the female until she lays eggs, to prevent other males from mating with her, Burne explained.

Male dragonflies are often territorial, defending sections of shoreline and chasing away other males, according to Mass Audubon.

Depending on the species of dragonfly, females deposit eggs directly into ponds, streams, or other bodies of water, or inject their eggs into plants growing in or near water with an organ called an ovipositor, said Mass Audubon.

When females deposit eggs into water, they fly over the surface and dip their abdomen into the water as they go, in a motion that looks like sewing, said Burne.

The eggs hatch into an aquatic larval stage called a nymph, said Mass Audubon. Dragonfly larvae are wingless, typically brown-colored, and about an inch or two in length. The larvae stalk prey as they walk along the bottom, or hide in debris in the water waiting to ambush aquatic organisms such as tadpoles, small fish, and invertebrates.

When the larvae complete their aquatic development, the nymph climbs out of the water, and its outer exoskeleton splits open, allowing the adult dragonfly to emerge, said Mass Audubon.

Biologist Tim Beaulieu holding two dragonfly larvae.Tim Beaulieu

The dragonfly larvae climb up plant stalks, but they also climb up other objects, like buildings, Burne explained. He said on his parents’ lake house in New Hampshire, he has found larval exoskeletons, called exuviae, 15 feet up the side of the house.

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The newly emerged adult dragonfly is called a teneral and is fragile and unable to fly at first, according to Burne.

“The teneral stage lasts for several hours while the exoskeleton hardens,” said Burne. “This is a dangerous time in the dragonfly life cycle, as they are unable to avoid predators, and they can drown if they’re washed off their perch.”

The larval stage of dragonflies’ lives lasts from several months to several years, depending on the species, while the adult stage only lasts from a few days to a few months, according to the “Field Guide to the Dragonflies and Damselflies of Massachusetts.”

Birds prey on dragonflies, but Burne said he’s also seen fish jump out of the water and take dragonflies from the air.

MassWildlife’s List of Endangered, Threatened, and Special Concern Species has several types of dragonflies listed as endangered, including the subarctic darner, the rapids clubtail, and the ebony boghaunter.

“Threats to dragonflies [and their aquatic larvae] include habitat loss and degradation,” said Burne. “And increasingly, the impact of pesticides on smaller insects that dragonflies prey on, as well as the decreasing number of insects generally, could have a trickle-down effect on dragonflies.”

And then, there’s the impact of the second-driest year on record since April. “The drought has almost certainly caused some problems for a lot of different species,” said Burne. “Premature drying of wetlands and waterbodies across the environmental spectrum — from ephemeral pools and small streams to sections of major rivers and larger ponds that may be drying out — will likely affect the survival of [dragonfly] larvae.”

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Some of the best places to see dragonflies are along the edges of bodies of water, like ponds and streams, and in wetlands, like swamps and bogs. One of my favorite local wetlands is the Pine Hole Bog, located on the Charles W. Ward Reservation on Prospect Road off of Route 125 in Andover. A boardwalk winds through the bog, and at the end of the boardwalk is a viewing area with a bench that looks out over the Pine Hole Pond. The pond is a good place to see a variety of dragonflies and other insects, as well as turtles, frogs, and numerous types of birds. The bog is also home to a variety of interesting plants. including sphagnum moss, wild cranberries, swamp horsetails, poison sumac, cotton grass, and insectivorous sundews and pitcher plants.

Send your questions about nature and wildlife in the suburbs to donlymannature@gmail.com.