Corollary

If you find one dragonfly odds are you will find more. This is a fundamental proposition of dragonfly observation (and most other insects as well). A corollary of that proposition: if you encounter a teneral dragonfly (one that has just emerged) odds are the nymph of that species can be found in the water closest at hand.

Having had the privilege to assist Bob Dubois, author of Damselflies of the North Woods in the field, I learned this corollary first hand. We were surveying dragonflies at the Agassiz National Wildlife Refuge near Thief River Falls, Minnesota. Another member of our survey team found a teneral Black Meadowhawk. Bob immediately set about dredging several nearby boggy puddles and before long had found several full grown nymphs. Ever since that day, when I've had the opportunity, I've made good use of this corollary.

Nymphs that are full grown are easy to rear, usually requiring only a few days or weeks before the adults emerge. Rearing young nymphs requires a whole different level of responsibility as some species can take years to become full grown. Because the identification of nymphs to species is difficult and there are no guidebooks yet, rearing a dragonfly nymph is a good way to identify it. Lately, I've become more and more interested in photographing the nymphs in addition to rearing them. And in this way help work toward a visual guide to the nymphs.

Having seen the teneral Eastern Forktail yesterday, I decided to look for nymphs today. At the catchment pond, it took a single pass through the silty shallows and cattail debris with the Tennessen racket (a racquetball racket with the strings replaced by steel mesh netting designed by Ken Tennessen) to find a number of damselfly nymphs. A few more swiffs through the bottom mud brought up a number of large skimmer dragonfly nymphs as well. Several large skimmer species have been observed at this pond. The most prevalent and the earliest to emerge is the Common Whitetail (Plathemis lydia). The nymphs closest to emergence, large in size and with full-sized wing pads, are probably this species. Checking the information on the nymph in The Odonata of Canada and Alaska: Volume 3 by E. M. Walker and P. S. Corbet, one morphological difference between the Common Whitetail nymph and the nymphs of the other large skimmers, such as Libellula pulchella and Libellula luctuosa is the absence of a dorsal hook on segment 6 of the abdomen. I can't help but notice that the eyes are striped, knowing that the adult eyes are striped as well.

Publicado el abril 25, 2017 04:24 MAÑANA por scottking