From the NY Times:
It is not clear whether there are more dragonflies in the city than in previous years, though many longtime New Yorkers say they have been startled because they had never seen the dragonflies before in those areas. Scientists also note that late July through September is migration season for some species of dragonflies, including the very large swamp darner. It is not clear whether the long period of cool weather this summer, which has compressed the period that dragonflies emerge, has affected their dispersion patterns.
New York City is home to at least 80 species of dragonflies, with the heaviest concentration of different species, 31, in Staten Island’s Ocean Breeze Park, according to the Parks Department, which tracks the insects. (Three of the species were discovered this year.) They are also famously resident in Central Park’s Belvedere Lake, where their trysting habits stymied Parks Department plans to to expand the park in 1987.
Photo from the City Birder