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AN HOUR WITH A DRAGONFLY

Although the splendors of spring have been unfolding at a rapid rate at Hilton Pond Center, we've not been able to immerse ourselves as usual in our surroundings--largely because we're preparing for the big John Bachman Symposium coming up at Newberry College, celebrating its 150th anniversary in 2006-07. Although the Rev. Bachman--founder of the College and a South Carolina contemporary of John James Audubon--is noted primarily for his expertise with small mammals, he also delved into other aspects of natural history such as birds (Bachman's Warbler!), flowering plants, and insects. We're not sure if Bachman devoted any time to studying aquatic invertebrates around his antebellum Charleston home, but we still thought about him this week during a rare free hour as we sat on the bank of Hilton Pond and tried to get photos of a hyperactive dragonfly.

All text & photos © Hilton Pond Center

We've been fascinated by dragonflies about as long as we can remember--or at least since early childhood when we visited the Carnegie Museum of Natural History in Pittsburgh and gazed at a diorama of the Carboniferous Era. Inside that display case, poised motionless over a depiction of a belly-dragging ancestral amphibian, was a model of Meganeura--a prehistoric dragonfly with two-foot wingspan! We had seen far smaller, modern-day dragonflies in our suburban Pittsburgh neighborhood, but to think there had been members of this family with wings the size of a double newspaper spread was almost beyond our comprehension. We expected dinosaurs to be big, but two-foot dragonflies? Unbelievable!

Today there are about 5,000 species of dragonflies worldwide, but the largest is a South American variety whose wingspan is a mere seven inches. Here in the Carolinas our biggest dragonflies are the darners, with body lengths and wingspans in the three-inch range. We have lots of experience with Common Green Darners, Anax junius, which occasionally get caught in mist nets we have unfurled to snare birds for banding. These nets also catch darners, and it's a pain to remove them because they tend to chomp down on a bander's fingers with surprisingly strong mouthparts.

The dragonfly we encountered this week at Hilton Pond wasn't a Common Green Darner--that species tends to appear later in the spring--but an appropriately named Blue Corporal, Libellula deplanata. (Blue Corporals are sometimes confused with the Eastern Pondhawk, Erythemis simplicicollis, as noted in our postscript.) The corporals, of which several species occur in the U.S., are small-sized dragonflies with nearly two-inch wingspans. In Blue Corporals, sexes are easily differentiated because adult males have a powder-blue abdomen, while females (and juvenile males) are brown with a row of black triangles down the abdomen's dorsal midline. Interestingly, we actually saw--and photographed--more than one male corporal in our hour this week on Hilton Pond, but no females were in evidence.

The Blue Corporal is one of the more widespread U.S. dragonflies, ranging throughout the Southeast and north to Massachusetts and southern Wisconsin, and west to eastern Nebraska and northcentral Texas. Here in the South Carolina Piedmont this species is one of the first dragonflies to emerge from its final nymphal stage, sometimes showing up in mid- to late March. And speaking of nymphs, during our one-hour sojourn we trained our telephoto lens on an iron rod sticking from the waters of Hilton Pond because a Blue Corporal was picturesquely posed on its tip (below left). It wasn't until the dragonfly sped after an intruder we realized it had been covering up the empty exoskeleton of a dragonfly nymph (below right. There's also a "shell" under the twig in the photo at the top of the page.)

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In Dragonflies through Binoculars (2000, Oxford University Press)-- perhaps the most useful field guide to North American species--Sidney W. Dunkle describes thusly the habitats of Blue Corporals:

[Inhabits] ponds, lakes, and occasionally trickles or streams. Most common at infertile waters such as sand-bottomed lakes or new borrow pits.

Male dragonflies in general are territorial, and they patrol their "property" tirelessly during the mating season, expelling other males and trying to mate with every female in sight. We've always been amazed at the aerobatics of large-easy-to-see dragonflies that seem able to stop on a dime and turn instantly as they pursue an intruder--or potential prey. Dunkle further describes feeding and mating behavior in the Blue Corporal:

Forages mostly from the ground. Males patrol from the bank or floating objects with a fast wavering flight and some hovering. The female does not splash water as she lays eggs [on the surface].

Among other things, Blue Corporals chase down and gobble up mosquitoes that pass through their territories, which makes them well worth protecting. It's probably fortunate, however, that our local dragonflies no longer have two-foot wingspans like those from the Carboniferous Era; otherwise they'd probably be eating small birds instead of insect pests. Nonetheless, we appreciate all dragonflies for their ability to catch and eat mosquitoes, and we suspect the Rev. John Bachman--who undoubtedly shared his Lowcountry 1850s home with a variety of blood-sucking bugs--would have enjoyed sitting on the banks of Hilton Pond to watch dragonflies this week, if only for an hour.

All text & photos © Hilton Pond Center
Fossil dragonfly photo courtesy New Mexico State University's Zuhl Library

POSTCRIPT: In our initial posting, we confused the Blue Corporal with the Eastern Pondhawk, another common Carolina dragonfly that is very similar in color. Pondhawks are slightly larger and far more aggressive, even preying on conspecifics. One way to differentiate the two species is to look at claspers on the end of the male's abdomen; in Blue Corporals these strucures are black, while in Eastern Pondhawks they are white. The pondhawk also has two obscure black streaks at the bases of its wings. Both corporals and pondhawks are in the Skimmer Family, Libellulidae.

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Be sure to scroll down for an account of all birds banded or recaptured during the week, plus other nature notes of interest.

"This Week at Hilton Pond" is written & photographed
by Bill Hilton Jr., executive director of
Hilton Pond Center for Piedmont Natural History.

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