Dragonfly, damselfly count dips in Delhi after extreme weather

A rain surplus leading to floods in the city followed by a deficient southwest monsoon may have impacted the breeding cycle of the insects

The overall dragonfly and damselfly count in the seven biodiversity parks in the Capital has dipped marginally when compared to last year, a three-day survey carried out by the Delhi Development Authority’s biodiversity programme has revealed. According to the survey, a combination of extreme weather events like a rain surplus in the first half leading to floods in the city followed by a deficient second half of the southwest monsoon may have impacted the breeding cycle of the insects and subsequently their count.

The survey was conducted from October 5-7 and found that the species count dipped in four out of the seven parks in Delhi. (HT Photo)

The survey was conducted from October 5-7 and found that the Kamala Nehru Biodiversity Park in north Delhi had the highest number of species (25), followed by 21 species at Yamuna Biodiversity Park in north Delhi. However, the species count dipped in four out of the seven parks in Delhi.

Faiyaz Khudsar, scientist-in-charge, DDA biodiversity parks programme, said extreme weather patterns appear to be causing a distribution range shift and suitable habitats were shrinking for these insects, which form a part of the “odonata” family. Odonatas are characterised by large round heads, compound eyes, two pairs of long, transparent wings and elongated abdomens.

“Higher water temperatures also cause the larvae to develop more quickly and emerge as adults sooner, thus affecting their availability throughout the monsoon due to their short life span. It has also been observed that the individuals that develop in warmer water also tend to develop smaller wings compared to their body size. As the relative wing size decreases, they will experience a higher wing load, making these individuals with less dispersal ability. This affects their ability to move around and predate harmful pests, including mosquitoes,” said Khudsar.

He added that dragonflies require marshy water bodies to breed and lay eggs and while ample water was available in the first half of the monsoon season, very little rain was recorded in August and September.

Experts said that the two species of insects play a vital role in the ecosystem, including controlling the mosquito and housefly population, with a single insect capable of consuming between 30 to 100 mosquitos a day.

The four parks where the count of insects has dipped include the 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 halved—to eight, compared to 16 different species last year.

At Kamla Nehru Biodiversity Park, the species count was the same as last year at 25. The count has increased at the two remaining biodiversity parks—Neela Hauz (from six last year to 13) and Tughlaqabad Biodiversity Park (from 7 last year to 14 species).

“Towards the end of the monsoon, a lot of smaller ponds dried up naturally. This has impacted the species count, though the overall numbers are higher than last year,” said Khudsar.

The Yamuna floods in July also disrupted the breeding season as shallow marshes turned into deep water bodies and the two biodiversity parks located along the river—Yamuna and Kalindi—recorded a drop in the overall species count. At Neela Hauz and Tughalaqabad, habitat restoration was carried out over the last year, which included building constructed wetlands. “This has provided them more habitats to breed locally,” he added.

Data shared by the biodiversity parks programme also showed a total of 2,563 individuals were recorded in this year’s count, which too is less than the 3,348 recorded last year.

Experts said the dip in dragonfly and damselfly count is possibly being reflected in the increased number of mosquitoes in the city. “A drop in their count invariably impacts the mosquito population, which can suddenly shoot up. The absence of proper rain in August, in particular, saw a lot of marshes dry up early, which meant some species were not found this year,” said CR Babu, head of the Centre for Environmental Management of Degraded Ecosystems (CEMDE).