Healthy ecosystems buzz with dragonflies
Insect's reemergence in Beijing an indication of positive changes
Nature's barometer
Huang Yue is an ecological restoration designer who has spent years rebuilding wetlands and urban water systems. She believes a dragonfly tells a more complicated story than simply whether a river looks clean.
In the summer of 2017, Huang was working on the restoration of a small 2,000-square-meter wetland on the outskirts of Beijing. It once contained a small pond, but changes to the surrounding river system and Beijing's low groundwater levels had caused it to leach away.
Huang and her colleagues restored the wetland. To keep the water from leaching again, an impermeable liner was put down on the ground surface.
"We then reintroduced native aquatic animals and planted submerged vegetation. As the ecosystem recovered, more dragonflies returned," she said.
"I remember one blade of grass with five dragonflies on it," Huang said, adding she was impressed by the sight.
In that small patch of wetland, she and her team identified between 20 and 30 species of dragonflies.
For Huang, who studied landscape architecture and urban biodiversity at Tsinghua University, the dragonfly is a useful way of reading an ecosystem.
But to thrive, a dragonfly needs more than just clean water. It requires aquatic vegetation for shelter, hunting and reproduction. It also needs suitable places along the shoreline to emerge from the water, and a food chain capable of supporting both predators and prey.
"To understand why dragonflies disappear — or why they return — you have to look at the whole ecosystem," Huang said.
Dragonfly larvae spend their early lives underwater, hiding among aquatic plants and ambushing prey such as mosquito larvae, tadpoles and small fish. Different species also use plants in different ways for reproduction. Some insert their eggs into the stems of aquatic vegetation, while others lay their eggs near aquatic plants.
When the larvae are ready to become adults, they climb out of the water and attach themselves to plants or other surfaces. The adult dragonfly slowly emerges, then unfolds and dries its wings before taking flight.
