(The collection in the Visitor's Center has one dragonfly in it. The Filigree Skimmer is in the middle of the collection. Below it on the right and left are two damselflies, their less robust relatives.)
For the past few days, large numbers of dragonflies have been evident flying in the late afternoon. In addition, at least locally, they all seem to be moving generally in the same direction, a fact which makes their presence even more conspicuous. Crossing the road to Frijole Ranch, they appear to be moving in a southerly direction. If you watch you will see that few, if any, are landing on the vegetation, although some might check it out.
Normally, we associate dragonflies with water. After all, the juvenile stage of the dragonfly is aquatic (depending on the species and its environment this can last 5 or more years) and looks quite different from the insects we normally call dragonflies (these are the adults). We usually notice dragonflies when they are flying near or over water, performing aerial maneuvers, as they chase and consume other insects, search for mates and lay their eggs. We do not think of dragonflies as roaming over the countryside, sometimes miles from the nearest pond or river.
When the juvenile aquatic phase is over, each juvenile dragonfly leaves the water and finds some secure support on which it can undergo its transformation from aquatic predator to aerial predator. This new, and more familiar, adult dragonfly is not capable of mating right away. What follows is a period of maturation, usually 1 to 2 weeks, during which the dragonfly leaves / avoids the water. During this time, the body and wings harden sufficiently to withstand the rigors of mating, the sex organs mature, and the colors of the body become more vivid. In some cases, the males undergo significant changes in body color.
Last evening, as it was raining, I went out to look for these dragonflies, so that I could identify them. I expected to find them resting in the vegetation, waiting out the passing storm. Instead I found that they were still flying, so I went down the highway out of the park. Since low flying dragonflies which cross major highways are sometimes hit and killed or damaged by cars and trucks, I searched along the side of the road for road killed or injured dragonflies. (NOTE: If you ever do this, do not become so engrossed with your task that you forget to watch the traffic. Youngsters need parental supervision.) I knew that my chances of finding road-kills were good because of the number of dragonflies on the move. Often you can find perfect or near perfect specimens, although visible eye / head and thoracic damage is common. Some may still be alive and others, particularly those that have been along the edge of the road for some time, may already be swarming with ants.
Along a short stretch of road, I recovered or saw about 15 dead and wounded dragonflies. All but one was a Spot-winged Glider, Pantala hymenaea. This species is a strong flier with wide-ranging habits. It is found over much of North America and ranges south to Chile and Argentina. It is also found on Bermuda, the Bahamas, the West Indies and the Galapagos Islands. (The one non-Glider was male Blue-eyed Darner, Aeshna multicolor. These have been around since the beginning of June, so I suspect this was likely just doing some late afternoon feeding.)
I don't know where the individuals we are seeing originated. However, Spot-winged Gliders breed in temporary ponds and pools in the open. This can include tanks and water troughs. With the recent wide-spread rains and warm weather, many of these areas will have held water long enough for some juveniles to complete their development. When large areas are subjected to the same environmental stresses, synchronized or nearly synchronized emergences and mass movements can occur.
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