June 11, 2014 —
Phenology, or the study of timing of seasonal events of plant and animal species from year to year, has been drawn more into the limelight in recent years due to concerns of climate change. Factors such as temperature, sun declination, seasonal change in cloud cover and precipitation are all thought to be factors in key events of a given species. Noting the time of the first call of a wood thrush, the sighting of the first painted turtle in a pond, or the occurrence of the first bald eagle egg in a nest can all be used to measure variances in timing of natural events.
One local event that I spotted this past week at Walker Lake in Shohola, PA was a large number of exuvia, or outer skins of dragonfly nymphs that were left behind on rocks and plant stems above the water line. An impromptu dragonfly survey followed, and it revealed that the exuvia probably belonged to a large number of lancet clubtails that were present, a species of dragonfly that emerges in this region at the start of June. The lancet clubtail is one of the first species of dragonfly to emerge in many areas during the spring.
There are upwards of 150 species of odonates (dragonflies and damselflies) in the region, and they emerge at different times of the spring and summer, making them excellent phenology indicators. For most of us, dragonflies are a welcome sight. They pluck mosquitoes and other biting insects out of the air, and the sight of them skimming over a pond means summer is soon to come.