The total number of dragonflies and damselflies in the capital’s seven biodiversity parks has declined marginally compared to last year, a three-day survey by the Delhi Development Authority’s biodiversity program has revealed. According to the study, a combination of extreme weather events, such as excess rainfall in the first half that caused flooding in the city, followed by a poor second half of the southwest monsoon, may have affected the insects’ reproduction cycle and, later, its count.
The survey was conducted from October 5 to 7 and found that Kamala Nehru Biodiversity Park in north Delhi had the highest number of species (25), followed by 21 species in Yamuna Biodiversity Park in north Delhi. However, the species count decreased in four of the seven parks in Delhi.
Faiyaz Khudsar, scientist-in-charge of the DDA’s biodiversity parks programme, said extreme weather patterns appear to be causing a shift in the range and suitable habitats are shrinking for these insects, which are part of the family ” odonata.” Odonata are characterized by having large round heads, compound eyes, two pairs of long transparent wings and elongated abdomens.
“Higher water temperatures also cause larvae to develop faster and emerge earlier as adults, which affects their availability during the monsoon due to their short lifespan. It has also been observed that individuals that develop in warmer waters also tend to develop smaller wings compared to their body size. As relative wing size decreases, they will experience greater wing loading, making these individuals less able to disperse. This affects their ability to move and prey on harmful pests, including mosquitoes,” Khudsar said.
He added that dragonflies need swampy bodies of water to breed and lay eggs and while there was plenty of water available in the first half of the monsoon season, very little rain was recorded in August and September.
Experts said the two species of insects play a vital role in the ecosystem, including controlling the population of mosquitoes and house flies, with a single insect capable of consuming between 30 and 100 mosquitoes a day.
The four parks where insect counts have declined include Yamuna Biodiversity Park in north Delhi, where 21 different species were recorded compared to 23 last year; the Aravalli Biodiversity Park (ABP) in south Delhi, where 11 species were recorded compared to 12 last year; Tilpath Valley Biodiversity Park in south Delhi, where five species were recorded compared to seven last year, and Kalindi Biodiversity Park along the Yamuna floodplains, where the count has been halved to eight, compared to last year’s 16 different species.
At Kamla Nehru Biodiversity Park, the species count was the same as last year, 25. The count has increased in the remaining two biodiversity parks: Neela Hauz (from six last year to 13) and Kamla Nehru Biodiversity Park. Tughlaqabad (from 7 last year to 14). species).
“Towards the end of the monsoon, many smaller ponds dried up naturally. This has impacted the species count, although the overall numbers are higher than last year,” Khudsar said.
The Yamuna floods in July also disrupted the breeding season as shallow mudflats turned into deep water bodies and the two biodiversity parks located along the river, Yamuna and Kalindi, recorded a drop in the overall count. of species. In Neela Hauz and Tughalaqabad, habitat restoration has been carried out over the past year, including construction of constructed wetlands. “This has given them more habitat to breed locally,” he added.
Data shared by the biodiversity parks program also showed that a total of 2,563 individuals were recorded in this year’s count, which is also less than the 3,348 recorded last year.
Experts said the drop in dragonfly and damselfly counts is possibly reflected in the increased number of mosquitoes in the city. “A drop in their count invariably affects the mosquito population, which can suddenly skyrocket. The absence of adequate rainfall in August, in particular, caused many marshes to dry out early, which meant that some species were not found this year,” said CR Babu, director of the Center for Environmental Management of Degraded Ecosystems (CEMDE).