Larval…
…something, or other.
Many of them, in fact. I think these might be lake midges, in the family Chironomidae.
And most of them seem to be just the larval husks, the exuviae, of the larval form.
The westerly breeze pushed them all to one part of the Sylvan Water. There were a heck of a lot of them: in this shot, they make up the cloudy looking area reaching uptimes to two from the shoreline.
This an adult non-biting midge. Same crew? They’re around, but nowhere near the numbers the water would suggest. They may spread, though. The other evening at sunset I noticed a cluster swarming at 4th floor level by Sunset Park, six or seven blocks as the midge flies from the Valley Water.
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This work by Matthew Wills is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.
Backyard and Beyond 
Yesterday I observed a feeding Louisiana Waterthrush in Central Park. It was picking many somethings that looked much like a shiny bubble out of the mud. I suspect it was the head end of these larvae. I think they were oriented vertically with just the top visible in the mud. The sunlight made them shiny and easy to locate. The bird fed consistently on them and probably consumed 30-50 in the 10 minutes I watched.
I’m looking at swarms of them at twilight and hoping for bats and nighthawks, but alas…
I wonder if that’s what I saw hovering in a cloud near 6th fl roof of my building. Watched them through binoculars- tricky! Their long drooping abdomens made me wonder if they were mosquitoes. But … maybe midges.
Interesting!
Yes, they like are really large mosquitos, but don’t sting or bite.
I, too, wanted to call any nearby bats or E. Phoebes to come and have some dinner!