Great Blue Skimmer

A dragonfly the color of faded denim cruising the tree line at a North Louisiana pond at chest height, larger than the blue dasher by a full half-inch, wearing chalky blue pruinescence across the entire body, and patrolling a beat that included both the open water the dashers claimed and the shaded forest edge the dashers avoided. The great blue skimmer (Libellula vibrans) filled the gap between the open-pond dashers and the forest-interior swamp darners by patrolling the transition zone where the pond met the trees, and the dragonfly's size, color, and habitat preference gave North Louisiana a big blue dragonfly that the blue dasher's smaller, brighter blue did not duplicate. About two inches to two and a quarter inches long, the great blue skimmer flew at North Louisiana ponds, lake margins, and forest-edge waterways from May through September. The dragonfly preferred ponds with adjacent wooded habitat rather than the open-pasture farm ponds the blue dashers dominated, and the forest-edge preference put the great blue skimmer at sites the birders already visited for warblers and flycatchers without knowing the dragonfly patrolled the same tree line. The Dusty Blue Giant Mature males wore chalky blue pruinescence across the thorax, abdomen, and face that gave the entire body a powdery, faded-denim appearance. The blue sat lighter and chalkier than the blue dasher's brighter pruinescence, and the color difference sorted the two blue dragonflies at close range: bright, saturated blue meant dasher. Chalky, pale, dusty blue meant great blue skimmer. Add the size difference (the skimmer sat half an inch longer than the dasher) and the two separated at binocular distance without any additional field marks. The face wore the same chalky blue as the body, and a head-on view of a perched great blue skimmer showed an entirely blue face that the dasher's green-eyed face did not match. Blue face plus chalky body plus large size equaled great blue skimmer at every pond where both blue dragonflies flew. Females wore brown and yellow on the thorax and abdomen with dark wing markings near the bases and tips that the males did not carry. A female great blue skimmer at a forest-edge pond showed broad brown wings (compared to the male's clear wings) and a brown body that blended into the shaded vegetation the female perched on between oviposition flights. Dark wing patches near the bases and tips on females (and to a lesser extent on some older males) added a wing field mark that the clear-winged blue dasher never showed. Wing patches plus large size plus forest-edge habitat confirmed the great blue skimmer at distances where the body color read ambiguously. The Forest-Edge Patrol Great blue skimmers patrolled the transition zone between open water and adjacent woodland at chest-to-head height, flying a beat that included the sunny pond margin, the shaded tree line, and the dappled-light corridor between the two. A great blue skimmer on patrol at a Lincoln Parish pond cruised from the open-water weed tips (where the dashers perched) to the shaded low branches at the forest edge (where no dasher ventured) and back again in a continuous circuit that bridged the two habitats without committing entirely to either. The forest-edge patrol put the great blue skimmer in contact with prey the open-pond dragonflies missed (forest-edge moths, beetles, and flies that stayed under the canopy) and prey the open-pond dragonflies shared (gnats, midges, and mosquitoes at the waterline). The dual-habitat patrol gave the skimmer a broader diet than either the pond-only dasher or the forest-only swamp darner accessed from their single-habitat beats. Territorial defense at the forest-edge patrol route involved chasing rival males along the tree line rather than over the open water, and two male great blue skimmers in a territorial confrontation spiraled along the forest edge at head height in a chase that followed the tree line's contour rather than flying out over the pond. The forest-edge chase path differed from the over-water territorial flights the dashers and pondhawks conducted, and the great blue skimmer's territorial behavior stayed anchored to the woodland edge the way the dasher's territorial behavior stayed anchored to the weed tips. Perching between patrol circuits happened on low branches, dead twigs, and vegetation at the forest edge rather than on the exposed weed tips at the waterline. A great blue skimmer perched on a dead twig at the edge of the tree canopy at a Winn Parish pond sat at chest-to-head height in dappled shade, and the chalky blue body against the dark woodland background caught the scanning eye better than the same blue body against the bright sky. The Shade Tolerance Great blue skimmers tolerated more shade than the blue dashers and pondhawks at shared ponds, and the shade tolerance explained the forest-edge patrol habitat the open-sun species avoided. A dasher that flew from an exposed weed tip into the shade at the tree line lost body temperature within minutes and returned to the sunny perch to reheat. A great blue skimmer that flew the same route into the same shade maintained flight temperature longer because the larger body mass held heat better than the dasher's smaller body mass, and the thermal inertia of the bigger body gave the skimmer permission to patrol the shaded edge that the smaller dragonfly's rapid heat loss prohibited. The shade tolerance expanded the great blue skimmer's effective habitat at any pond with adjacent woodland. A pond that offered fifty feet of sunny waterline and a hundred feet of shaded forest-edge waterline gave the dasher fifty feet of usable patrol zone and gave the great blue skimmer a hundred and fifty feet of usable patrol zone. The skimmer's bigger range included the dasher's entire sunny range plus the shaded range the dasher could not use, and the habitat math favored the skimmer at every pond where woodland bordered the water. Cool mornings and overcast days that grounded the smaller, heat-dependent dashers left the great blue skimmer still flying because the larger body needed a lower air temperature to reach the higher body temperature the smaller dragonflies' thin bodies lost too fast. A great blue skimmer cruising the forest edge at a North Louisiana pond on a 72-degree overcast July morning flew alone over water that held ten grounded blue dashers on the weed tips below, and the skimmer fed without competition during the cool-weather window the dashers' physiology closed. Wind at the Forest Edge Wind affected the great blue skimmer less dramatically than wind affected the blue dasher because the skimmer's larger body mass resisted the wind force better and because the forest-edge habitat blocked the wind more effectively than the open-water habitat the dasher occupied. A fifteen-mile-per-hour wind at a North Louisiana pond grounded every blue dasher on the exposed weed tips while the great blue skimmer continued patrolling the forest edge where the tree canopy broke the wind speed to half the open-water velocity. The forest-edge wind shadow gave the great blue skimmer a calm-air flight corridor during windy conditions that the open-water species could not access. A skimmer cruising the lee side of a tree line during a breezy July afternoon flew in five-to-eight-mile-per-hour air while the dashers two hundred feet away at the open waterline sat in fifteen-mile-per-hour air that grounded the smaller dragonfly. The wind shadow and the shade operated from the same trees, and the forest gave the skimmer two advantages (wind protection and shade tolerance) from a single habitat feature. Roosting in the Canopy Great blue skimmers roosted overnight in the lower canopy of the woodland adjacent to the breeding pond rather than on the pond-margin vegetation the dashers used. A roosting great blue skimmer on a branch ten feet above the ground inside the tree line sat higher, more concealed, and better protected from ground predators than a dasher roosting on a weed stem two feet above the waterline. Morning warm-up happened on east-facing branches that caught the first sunlight through the canopy gaps, and the skimmer descended from the canopy roost to the forest-edge patrol route as the morning sun warmed the body to flight temperature. A great blue skimmer that left the overnight roost at 8:30 a.m. on a June morning flew directly to the forest-edge patrol beat and began the day's first feeding circuit within minutes of reaching the pond, and the canopy-to-pond commute took under thirty seconds of flight. The Big-Body Advantage Size gave the great blue skimmer advantages beyond shade tolerance at shared ponds. A great blue skimmer outmassed the blue dasher, the pondhawk, and the amberwing at every encounter, and the size advantage translated into territorial dominance over every smaller dragonfly at the forest-edge patrol zone. A dasher that wandered from the open-water weed tips into the skimmer's forest-edge territory got chased back to the open water within seconds, and the skimmer's pursuit ended the incursion without physical contact because the dasher recognized the size disadvantage and retreated rather than fighting. Feeding on larger prey items gave the skimmer more calories per catch than the dasher's gnat-and-midge diet delivered per catch. A great blue skimmer that caught a moth at the forest edge consumed a prey item that weighed five to ten times what a dasher's average gnat weighed, and the calorie advantage per catch meant the skimmer fed less frequently than the dasher while maintaining equal or greater daily calorie intake. Fewer sallies, bigger meals, more time perching between catches. The size disadvantage: a great blue skimmer that encountered a common green darner at a shared pond sat on the wrong side of the same size hierarchy the skimmer enforced over the dashers. A darner that descended from head height into the skimmer's patrol zone chased the skimmer out of the patrol zone with the same casual authority the skimmer used on the dashers, and the food chain at a North Louisiana pond ran darner > skimmer > pondhawk > dasher > amberwing from top to bottom. The May-to-September Calendar Great blue skimmers in North Louisiana flew from May through September, with peak adult activity in June and July when the emergence wave from the overwintering naiad population crested and the longest days gave the shade-tolerant skimmer maximum feeding hours at the forest edge. May brought the first adults at warm-water, wooded ponds. June peaked the adult count. July sustained peak density. August thinned the population as the oldest adults died. September brought the last adults before the shortening days and cooling nights ended the flight season. The flight season matched the blue dasher's calendar closely, and both blue dragonflies flew at shared ponds for the entire May-through-September window. The coexistence at shared ponds depended on the habitat separation (skimmer at the forest edge, dasher at the open water) rather than on any temporal separation, and both species occupied the same pond simultaneously without the calendar sorting them. Emergence at forest-edge ponds happened along the wooded margin rather than at the open waterline, and exuviae (shed larval skins) on tree roots, low branches, and emergent vegetation within the shade confirmed emergence sites that the open-water scans did not cover. A great blue skimmer naiad climbing a cypress root two feet above the waterline under the canopy emerged in shade that the open-water-emerging dashers never chose, and the emergence-site preference matched the adult's shade-tolerance the way every life-stage preference aligned with the forest-edge niche. Telling the Blues Apart North Louisiana supported three blue-bodied dragonflies at many shared ponds (great blue skimmer, blue dasher, and blue corporal in early season), and sorting the three demanded different field marks for each pair. Great blue skimmer versus blue dasher: the skimmer sat larger (two inches versus one and a half inches), chalkier (pale dusty blue versus brighter saturated blue), and perched at the forest edge rather than at the open waterline. Size read at binocular distance, the chalky-versus-bright blue read at close range, and the perch location told the story at any distance. Great blue skimmer versus blue corporal: the corporal flew in February and March and largely finished by June when the skimmer peaked. Calendar separated the two at most ponds. During the brief May overlap, the corporal sat smaller, flatter-bodied, and more open-water-oriented than the skimmer. Both wore blue pruinescence, but the corporal's blue leaned more toward true blue while the skimmer's blue leaned more toward chalky powder. Blue dasher versus blue corporal: the corporal flew earlier (February through May) and sat broader-bodied and flatter than the dasher. The dasher's green eyes separated it from both the corporal and the skimmer at face-view range. All three blue dragonflies at the same North Louisiana pond in May sorted by size, shade tolerance, flight season timing, and eye color without any single field mark doing all the work. The Dusk Patrol Great blue skimmers extended the patrol into later afternoon and earlier dusk than the blue dashers at shared ponds, and the shade tolerance that let the skimmer fly the forest edge also let the skimmer fly in the lower light levels of late afternoon when the smaller, sun-dependent dashers grounded. A great blue skimmer cruising the forest edge at a Winn Parish pond at 6:30 p.m. on a July evening flew in light conditions that sent every blue dasher at the same pond to a roosting perch thirty minutes earlier. The late-afternoon patrol put the great blue skimmer over the pond during the mosquito-emergence spike that happened at dusk, and the skimmer ate mosquitoes during the hour of maximum mosquito activity that the dashers and pondhawks missed because the smaller species stopped flying before the mosquitoes started swarming. A great blue skimmer feeding at dusk along the forest edge of a North Louisiana pond intercepted the evening mosquito wave that the daytime dragonflies left for the bats. Extended activity hours (earlier start on cool mornings, later end on summer evenings) gave the great blue skimmer more total feeding hours per day than the blue dasher logged at the same pond, and the hourly advantage accumulated across the flight season into a meaningful difference in total prey consumed per adult per season. More hours meant more food meant more calories for egg development and for surviving the daily predation pressure. Breeding at the Shaded Pond Great blue skimmers bred at ponds and slow-water margins with adjacent woodland, and the breeding habitat required both water (for naiad development) and trees (for the adult's forest-edge patrol and perching). A farm pond in open pasture without any adjacent trees attracted dashers and pondhawks but not great blue skimmers because the woodland component did not exist. A farm pond with a tree line on one side attracted all three species because the tree line gave the skimmer the forest-edge habitat the dasher did not need. Females oviposited by tapping eggs onto the water surface at shaded or partially shaded sections of the pond near the forest edge, and the oviposition flights covered the transition zone between the open water and the overhanging canopy. A female great blue skimmer dipping eggs at the shaded waterline of a Claiborne Parish pond deposited eggs under the canopy where the water temperature sat cooler than the open-water surface the dashers oviposited over. Males guarded the ovipositing female from forest-edge perches rather than from hovering positions over the water, and the perch-guard strategy let the male monitor the oviposition area from the shade while the female worked the waterline below. A male on a dead twig above a female's oviposition site scanned for rival males and launched interceptions from the perch without leaving the shaded zone the male's thermal comfort required. The Canopy-Water Connection A great blue skimmer female choosing an oviposition site selected the shaded waterline near the overhanging canopy rather than the sunny open water the dashers oviposited over, and the shade-oviposition preference placed the eggs in water that developed a thicker layer of leaf litter on the bottom (from the canopy's leaf drop) than the open-water bottom accumulated. The eggs sank into the same leaf-litter environment the naiads would grow up in, and the oviposition-site choice matched the naiad's habitat preference before the naiad hatched. A farm pond with trees on the south bank and open pasture on the north bank attracted great blue skimmer oviposition exclusively along the south bank where the canopy overhung the water, and the female never crossed to the open north bank for egg-tapping despite the north bank holding more blue dashers, more pondhawks, and more of every open-water species. The tree side got the skimmer eggs. The open side got the dasher eggs. The two species sorted breeding habitat at the same pond without overlapping oviposition zones. The Naiad in the Leaf Litter Great blue skimmer naiads developed in the leaf litter and organic debris at the bottom of shaded ponds, and the naiad's habitat preference mirrored the adult's shade tolerance: leaf-covered bottom in shaded water near the wooded margin. Development lasted roughly one year, and the naiad grew through multiple molts in the dark water under the leaf layer before climbing a plant stem or a tree root above the waterline one May morning. The naiad's size at emergence ranked among the larger skimmer naiads in North Louisiana (smaller than a darner naiad, larger than a dasher naiad), and the naiad fed on mosquito larvae, midge larvae, damselfly naiads, and tadpoles throughout the twelve-month development period. The Shaded Naiad Leaf-covered bottom in shaded water near the wooded margin near the wooded margin explained why great blue skimmer naiads appeared at ponds with forest on at least one side and did not appear at open-pasture ponds without any canopy. The leaf litter that accumulated under the trees gave the naiad concealment, prey (leaf-litter invertebrates), and the cooler water temperatures the shade maintained, and the shaded-bottom habitat differed from the open-mud habitat the dasher naiad tolerated at every exposed farm pond. Fish predation on great blue skimmer naiads followed the same pattern every pond-breeding dragonfly faced: bass and bluegill ate the naiads at every size class, and the naiad survived through concealment in the leaf litter rather than through speed or size. A great blue skimmer naiad buried in a six-inch layer of decomposed leaves at the shaded margin of a Claiborne Parish pond sat hidden from the bass scanning the open water three feet away, and the leaf concealment reduced the fish encounter rate below what the open-bottom naiads of other species experienced. The twelve-month development period meant the naiad survived two seasonal transitions (fall and spring) and one full North Louisiana winter in the cold water. Winter growth slowed dramatically as the water temperature dropped, and the naiad sat dormant in the leaf litter from December through February before warming water in March restarted the growth that culminated in the May emergence. What Hunts the Great Blue Skimmer Common green darners caught great blue skimmers from above during patrol encounters at shared ponds. A darner that descended from head height intercepted a skimmer cruising the forest edge at chest height, and the darner's size advantage made the interception a foregone conclusion the skimmer avoided only by reaching the cover of the tree canopy before the darner closed the gap. Birds at the forest edge (eastern phoebes, Acadian flycatchers, eastern wood-pewees) caught great blue skimmers from low perches in the same habitat zone the skimmer patrolled. A phoebe on a low branch at the forest edge sallied for the skimmer with the same technique the phoebe used on moths, and the skimmer's forest-edge patrol put the dragonfly in the flycatcher's primary hunting zone. Spiders strung webs across gaps at the forest edge and caught skimmers in flight. A golden orb-weaver web at the transition between the open pond and the tree canopy intercepted skimmers cruising the boundary, and the web's position at the habitat edge targeted the exact flight path the skimmer's patrol followed. Where to Look North Louisiana ponds and lake margins with adjacent woodland from May through September. Scan the tree line at chest-to-head height for a large, chalky blue dragonfly cruising the boundary between the open water and the forest edge. The great blue skimmer patrolled the shade-sun transition rather than the open water, and the observer who scanned the tree line found skimmers the open-water scan missed. Kisatchie National Forest ponds, Black Bayou Lake wooded margins, Lake Claiborne coves with overhanging trees, and any North Louisiana pond bordered by hardwood forest on at least one side put great blue skimmers within binocular range from the bank during the summer flight season. Forest-edge trails that paralleled pond shorelines gave the observer a walking beat that followed the same corridor the skimmer patrolled, and a slow walk along a wooded pond margin in June encountered great blue skimmers at the same perches the walk encountered phoebes and pewees. The Forest-Pond Connection Finding great blue skimmers in North Louisiana came down to finding the right ponds: water with trees. A pond in open pasture without any woodland within a hundred feet attracted dashers, pondhawks, and amberwings but did not attract great blue skimmers. A pond with mature hardwood forest on one or more sides attracted all the open-pond species plus the great blue skimmer, and the skimmer's presence confirmed the woodland-water connection the open-pond species did not require. The practical search strategy: skip the open-pasture ponds and target the wooded ponds. Kisatchie National Forest ponds, beaver ponds in forested drainages, farm ponds with tree lines on the south or west bank, and any North Louisiana pond where the canopy reached within thirty feet of the waterline attracted great blue skimmers during the June-through-August peak. The birder who already walked the wooded pond margin for warblers walked the great blue skimmer's habitat without changing the route. Where to Learn More Dennis Paulson's Dragonflies and Damselflies of the East covers the great blue skimmer's forest-edge habitat, the chalky blue pruinescence that separated the skimmer from the blue dasher, and the female's dark wing patches that the male's clear wings did not carry. OdonataCentral.org maintained records and photographs for the great blue skimmer's Louisiana distribution. Experiencing This Dragonfly: Accessibility Notes Great blue skimmers make no sound human ears detect, but the large size and chalky blue coloring made visual detection easier than most dragonflies at the same pond. The forest-edge patrol at chest-to-head height put the skimmer within direct sightline of any observer standing or sitting at the pond margin near the tree line. For anyone with mobility limitations, accessible pond edges adjacent to woodland put great blue skimmers within binocular range from the bank. A park bench or a wheelchair at a shaded pond margin near the tree line sat at the correct height and in the correct habitat zone to intercept the skimmer's patrol circuit as the dragonfly cruised past at chest height. The skimmer flew the forest edge repeatedly on the same patrol route, and the observer who waited at one spot along the route caught the skimmer's pass every two to four minutes without moving.

Accessibility

Great blue skimmers make no sound human ears detect, but the large size and chalky blue coloring made visual detection easier than most dragonflies at the same pond. The forest-edge patrol at chest-to-head height put the skimmer within direct sightline of any observer standing or sitting at the pond margin near the tree line.

For anyone with mobility limitations, accessible pond edges adjacent to woodland put great blue skimmers within binocular range from the bank. A park bench or a wheelchair at a shaded pond margin near the tree line sat at the correct height and in the correct habitat zone to intercept the skimmer's patrol circuit as the dragonfly cruised past at chest height. The skimmer flew the forest edge repeatedly on the same patrol route, and the observer who waited at one spot along the route caught the skimmer's pass every two to four minutes without moving.