Dragonfly Dramas

Desert Whitetails and Flame Skimmers cavort in the sinkholes of New Mexico's Bitter Lake Refuge

  • By Jake Page
  • Smithsonian magazine, January 2002

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    (Page 2 of 2)

    So why are there so many Odonata here? At first glance, their presence seems unlikely. After all, Bitter Lake lies at the northern edge of the Chihuahuan Desert, a refuge known mostly for its birdlife, especially its spectacular winter flocks of snow geese and sandhill cranes. It is a flat landscape lying west of a long low ridge called Comanche Hill. The Pecos River runs along the ridge, and the refuge itself contains many lakes left over when the river took a new course. The alkaline lakes for which the refuge is named are indeed bitter, making it the kind of place Louis L’Amour heroes steer clear of.

    Right where the Chihuahuan Desert meets the shortgrass prairie, Larsen told me, is an extremely diverse habitat for plant species. In addition to freshwater sloughs, ponds, marshes, springs, ditches and a half-mile-long stream known as the Lost River, the refuge contains more than 60 sinkholes. This is ideal habitat for dragonflies.

    Sinkholes are just as they sound—places where soluble bedrock dissolves, creating cavities or holes in the surface. Groundwater then often fills the hole. The process is typically slow, but local legend has it that one of the refuge’s sinkholes formed overnight beneath a parked bulldozer. Some sinkholes here are but a few feet across, though one is large enough—about an acre—to be called (with a bit of exaggeration) Lake St. Francis, 70 feet deep with beautiful blue and Caribbean-green water. These sinkholes have become aquatic "islands" in this arid desert habitat.

    Sinkhole conditions differ a great deal. Some have steep, naked gypsum sides; others have reeds and grasses that grow right up to the water’s edge. In some sinkholes, the water is so saline that it supports red and green algae blooms. Other sinkholes are saltier than seawater and invite species of dragonflies and damselflies usually found in estuaries, although the nearest seashore is a thousand miles away. The unique blend of conditions in each sinkhole creates entirely different ecosystems, even though one sinkhole may be only ten feet from another. As a result, each sinkhole, Gaines explained, seems to have its own special array of Odonata, and some species breed only in a single sinkhole. (Sinkholes also host the only known populations of certain other animal species, such as the last genetically pure species of the extraordinarily salt-tolerant Pecos pupfish and certain springsnails and amphipods.) "It’s a natural outdoor laboratory," Gaines said.

    She keeps track of this confusing and colorful aerial menagerie with a little biological sleuthing. Gaines regularly places little ladders of wire mesh leading from the edge of sinkholes into the water. Because Odonata leave their larval casing on the ladder as they crawl out, she can identify which species breed in the Bitter Lake sinkholes and which migrate here after breeding elsewhere.

    Nearby Roswell may be a mecca for UFOs, but the dedicated scientists here at Bitter Lake have a pretty good handle on what’s flying around. Already, I can spot the fluttering flight of the desert whitetail (Libellula subornata) and the bright red body of the flame skimmer (L. saturata). I was struck by how much these Odonata folk sounded like bird-watchers, singing out the name of a dragonfly they see whizzing by for but an instant. Indeed, the common names of these creatures are just as exciting as bird names—or more so.

    After all, where’s the poetry in spotting a crow or a snipe? But imagine spotting an Eastern amberwing, a seaside dragonlet or a Halloween pennant during a single outing at your neighborhood pond. And if your life list included the Comanche skimmer, the desert forktail and the black saddle bags, wouldn’t your chest swell with pride?

    by Jake Page

    "Gomphid!" someone shouted, and the little thing with the gleaming fuselage hovered, then sped away. I was standing on the whitish gypsum-rich hardpan that passes for soil in the desert about 15 miles north of Roswell, New Mexico. The air around me was filled with mostly unidentified flying objects.

    I now knew that this yellow-and-black creature was a Gomphid, a genus of dragonfly. But many of the dozens of other Odonata, the general scientific name for dragonflies and damselflies, which flew aerial gymnastics around me, remain nameless. This particular location—the Bitter Lake National Wildlife Refuge—hosts a great variety of these curious creatures.

    My expert guide, Robert R. Larsen, is a well-built man who carries a big white net as comfortably as many men carry a briefcase. By training a botanical illustrator and by preference a biological "investigator," Larsen was the scientist to whom the managers of the Bitter Lake National Wildlife Refuge turned when they identified an unusually large number of Odonata species helicoptering around the sinkholes of the refuge in 1998.

    With funds from the state Game and Fish Department, Larsen—a resident of Roswell who had been analyzing the plant life of the refuge—netted more than 50 species of dragonfly and some 30 species of damselfly. They included the largest dragonfly found in the United States (Anax walsinghami) and one of the nation’s smallest damselflies (Ischnura hastata). An easy way to distinguish between a dragonfly and a damselfly is to observe the wings: the rear, or posterior, pair of dragonfly wings are broader than the front, or anterior, pair, while both sets of a damselfly’s wings are essentially equal in size.

    Other distinguishing characteristics include the eyes of the damselfly, which are on opposite sides of its head, while dragonfly eyes are typically closer together, sometimes even connected. These bulging and usually colorful organs have up to 30,000 facets. Both creatures, however, enjoy expanded peripheral vision, a formidable feature for a predator, which both dragonflies and damselflies become early on in their lives.

    "I’m really glad the larvae aren’t huge, or that I’m not really small," said Karen Gaines, a graduate student at the University of New Mexico who has been studying Odonata larvae at the refuge. Most dragonfly larvae, which are aquatic for one to two years, are utterly insatiable, eating everything they come across, including tadpoles, fish, and mosquito and other insect larvae. They even eat their own siblings.

    Eventually, the larva climbs out of the water; its outer "skin," or exoskeleton, splits open, it pulls its telescoped abdomen out of the casing and it gradually extends to full length. Within one to two hours, the wings clear, dry out and open up. After its wings harden, over the course of several hours to several days, the creature will become a remarkable aerialist. Some species can fly up to 35 miles per hour. Their wings work independently, so they can hover and change direction instantaneously. Some species are migratory and, with the wind’s help, may travel hundreds of miles.

    Adult life is relatively brief, typically a matter of weeks, though some species can live for as long as a year. The time is spent voraciously feeding on mosquitoes, assorted moths and butterflies, and mating, a complex affair that turns a pair into an acrobatic and often airborne pretzel. Larsen reports seeing a large dragonfly carry off a minnow, a sight so remarkable that other scientists have questioned him on it. While I was standing right next to her, Karen Gaines swished her net in the air and caught a Gomphus militaris with the wing of a damselfly still hanging from its mouth. (Additional excellent detail about the biology of Odonata is covered in Smithsonian Institution Press.)

    So why are there so many Odonata here? At first glance, their presence seems unlikely. After all, Bitter Lake lies at the northern edge of the Chihuahuan Desert, a refuge known mostly for its birdlife, especially its spectacular winter flocks of snow geese and sandhill cranes. It is a flat landscape lying west of a long low ridge called Comanche Hill. The Pecos River runs along the ridge, and the refuge itself contains many lakes left over when the river took a new course. The alkaline lakes for which the refuge is named are indeed bitter, making it the kind of place Louis L’Amour heroes steer clear of.

    Right where the Chihuahuan Desert meets the shortgrass prairie, Larsen told me, is an extremely diverse habitat for plant species. In addition to freshwater sloughs, ponds, marshes, springs, ditches and a half-mile-long stream known as the Lost River, the refuge contains more than 60 sinkholes. This is ideal habitat for dragonflies.

    Sinkholes are just as they sound—places where soluble bedrock dissolves, creating cavities or holes in the surface. Groundwater then often fills the hole. The process is typically slow, but local legend has it that one of the refuge’s sinkholes formed overnight beneath a parked bulldozer. Some sinkholes here are but a few feet across, though one is large enough—about an acre—to be called (with a bit of exaggeration) Lake St. Francis, 70 feet deep with beautiful blue and Caribbean-green water. These sinkholes have become aquatic "islands" in this arid desert habitat.

    Sinkhole conditions differ a great deal. Some have steep, naked gypsum sides; others have reeds and grasses that grow right up to the water’s edge. In some sinkholes, the water is so saline that it supports red and green algae blooms. Other sinkholes are saltier than seawater and invite species of dragonflies and damselflies usually found in estuaries, although the nearest seashore is a thousand miles away. The unique blend of conditions in each sinkhole creates entirely different ecosystems, even though one sinkhole may be only ten feet from another. As a result, each sinkhole, Gaines explained, seems to have its own special array of Odonata, and some species breed only in a single sinkhole. (Sinkholes also host the only known populations of certain other animal species, such as the last genetically pure species of the extraordinarily salt-tolerant Pecos pupfish and certain springsnails and amphipods.) "It’s a natural outdoor laboratory," Gaines said.

    She keeps track of this confusing and colorful aerial menagerie with a little biological sleuthing. Gaines regularly places little ladders of wire mesh leading from the edge of sinkholes into the water. Because Odonata leave their larval casing on the ladder as they crawl out, she can identify which species breed in the Bitter Lake sinkholes and which migrate here after breeding elsewhere.

    Nearby Roswell may be a mecca for UFOs, but the dedicated scientists here at Bitter Lake have a pretty good handle on what’s flying around. Already, I can spot the fluttering flight of the desert whitetail (Libellula subornata) and the bright red body of the flame skimmer (L. saturata). I was struck by how much these Odonata folk sounded like bird-watchers, singing out the name of a dragonfly they see whizzing by for but an instant. Indeed, the common names of these creatures are just as exciting as bird names—or more so.

    After all, where’s the poetry in spotting a crow or a snipe? But imagine spotting an Eastern amberwing, a seaside dragonlet or a Halloween pennant during a single outing at your neighborhood pond. And if your life list included the Comanche skimmer, the desert forktail and the black saddle bags, wouldn’t your chest swell with pride?

    by Jake Page


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    Comments

    thanks-- this is a good model, but it's time for another dragonfly story, so I have it for you with good pictures coming. really beautiful pictures on your way. they are very hard work, almost as difficult as lycaenidae...

    Posted by pogo on May 17,2008 | 09:59AM

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