Life History and Distribution of the Hine’s Emerald Dragonfly
Hine’s emerald dragonflies are found in small isolated populations that are heavily fragmented due to human encroachment and development. In the United States, they are currently found only in Illinois, Wisconsin, Michigan, and Missouri. Their distribution is limited because Hine’s have specific habitat requirements that must be met in order to allow them to survive.
Hine’s require spring or seep-fed streamlets that are clean and cool, dry for part of each year, and are underlain by dolomitic rock. Most dragonfly larvae of other species, as well as other predators that would feed on the Hine’s emerald larvae, die during these dry cycles, reducing the number of species Hines’ must compete with for food and shelter. Discovering how the Hine’s emerald larvae survive these dry periods was the result of much time and effort on the part of researchers.
Example of habitat wetting and drying cycles
Hine’s emerald dragonfly larvae have a protracted larval stage lasting 4 to 5 years in which they live in the streamlet habitats and take refuge in crayfish burrows. During this time they feed on small aquatic organisms such as isopods, midge larvae, and amphipods. During the late summer of their 4th or 5th year they crawl out of the water on a plant stem, or some other structure and emerge as an adult dragonfly. This is a dangerous time for an emerging adult because even a stray gust of wind can knock it off its perch, resulting in death or deformity.
One of the secrets to the survival of Hine’s emerald larvae during dry periods and winter months is the presence of burrowing crayfish. Larvae take refuge in these extensive burrows until conditions improve above ground. How they remain undiscovered and uneaten in burrows with crayfish that will readily consume them is still being studied.
Adult Hine’s emerald dragonflies live for only a few weeks from mid to late summer. During this time they feed on various small flying insects they capture while on the wing. Females, after mating, will lay their eggs in the small streamlets by either depositing the eggs in the water or by placing them into the mud along the edges of the streamlets. The eggs will overwinter in the mud and then hatch the following spring as the water temperature increases, beginning the cycle again.