Sticky heat. Smoke in the skies. And now swarms of bugs?

Summer is off to an icky start in New York as clouds of gnats blanketed the city Thursday night, getting inside the subway system and grossing out runners, bikers and strollers across the boroughs.

But don’t worry, they’re not a sign of doom. In fact, one bug expert told THE CITY they’re an indicator of a “healthy environment.”

The green and white flies who swarmed your block this week are aphids, the common garden pest, who go through many life stages in a season, said David Grimaldi, a curator and entomologist at the American Museum of Natural History.

Aphids have synchronized development, meaning they transition to a new stage of life all at the same time. What New Yorkers are seeing now is the winged stage, he said.

“When a population becomes very large … the emergence of winged morphs is impressive,” Grimaldi said by email. “The good news? It means we have a healthy environment! No pesticides!”

Aphids are annoying, but not harmful to humans, experts said. But urban gardeners may not be too pleased.

“If you’re a plant and the aphids are landing on you, you’re not thrilled because they’re going to be sucking nectar out of your leaves and stems,” said Gil Bloom, an entomologist at Standard Pest Management in Astoria. “But it’s a natural occurrence.”

“I’d be a little bit more concerned about the spotted lantern flies,” he added.

A cool spring and slightly drier conditions may have given rise to more aphids, experts said. But it’s unlikely that the other plague on the city, wildfire smoke, affected the winged bugs in any way — despite guesses on social media that the bugs were the same as critters seen during smoky conditions on the West Coast.

“I think we’ve become way too apocalyptic,” Bloom said, laughing. “Maybe for good reason! I know it does kind of seem like a never-ending cascade of maladies.”

The answer, said Jody Gangloff-Kaufmann of the New York State Integrated Pest Management Program at Cornell University, is much more mundane.

“We have just entered some sustainably warm summer temps and I would guess that this has triggered a mass migration of winged aphids,” she said by email.

“Like most things, this will stop as quickly as it started.”