A survey of dragonflies and damselflies at Delhi’s biodiversity parks indicates that low rainfall this year may have impacted their life cycles and numbers.
In a week-long survey that concluded on Sunday, a total of 25 species of dragonflies and damselflies were recorded across the biodiversity parks and the Kamla Nehru Ridge.
The Kamla Nehru Ridge recorded the maximum number of species – 25. The Yamuna Biodiversity Park recorded 23 species, a little less than the 25 species recorded in 2018. In terms of the number of individuals recorded, the Kalindi Biodiversity Park recorded the highest number at 3,348, followed by the Aravalli Biodiversity Park where 555 individuals were counted.
The last such survey was conducted in 2018 at the Yamuna, Tilpath Valley and Neela Hauz Biodiversity Parks. The Neela Hauz biodiversity park also recorded a fewer number of species this year – just six – as compared to 2018, when nine species were counted.
Species that were recorded include the Scarlet Skimmer, Picture Wing dragonfly and the Granite Ghost.
In addition to counting the number of species in the two main ecosystems of Delhi – the Aravallis and the Yamuna – the survey was also meant to determine whether the deficit in rainfall in Delhi this monsoon has had any impact on dragonflies and damselflies.
Faiyaz Khudsar, scientist in-charge, Biodiversity Parks Programme at the Centre for Environment Management of Degraded Ecosystems, said, “Since the temperature was high and rainfall was low, there was little water in the river and the floodplain wetlands are shrunken. The nymph, which is one of the stages of the life cycle of the dragonfly, stays in the water for a long period of time and is a voracious feeder of mosquito larvae. When the temperature is high and there’s less rainfall and less water, the nymph grows quickly into an adult. Since dragonflies have small life spans, they die quickly. That’s the scenario this time.”
“When the temperature is high and the metamorphosis is faster, the wing size also tends to reduce. And, when the wing size reduces, their dispersal can reduce drastically. Since their movement is reduced, their foraging – they feed on adult mosquitos – is also reduced,” Khudsar added.
The city has recorded a deficit in rainfall for the monsoon so far. For the month of September, there was a large deficit in rainfall till this week when monsoonal rainfall picked up again.
With rainfall having picked up towards the end of the week, the scientists noticed that the dragonflies began laying eggs again. “They have started breeding again thinking that it is the monsoon. Soon, winter will come, and what’s going to happen to those eggs?” Khudsar said.
Collecting data of this sort for a few years can help track the changes taking place in the ecosystem, and it could be too soon now to arrive at concrete conclusions, he added.
Dragonflies serve as biological control for mosquitoes. They are also an indicator of water quality in wetlands and water bodies since polluted water is detrimental to them.