First the smoke. Then the insects.

It has been described as a plague and a sign of the end times, making New York City the “Bug Apple”.

Insects can descend in unusual swarms in populated places for various reasons, for example, in the mating season or in search of food. But New Yorkers who were plagued by clouds of tiny bugs this week have wondered if they were getting another consequence of the choking smoke drifting in from Canadian wildfires.

As swarms of insects swept the city’s skyline, blanketing the muted skylines of skyscrapers with a swirling bug cloud at street level, some New Yorkers complained that they couldn’t open their mouths to breathe as they walked down the street for fear of breathing in a big sip from them.

Pedestrians hit as they walked. Outdoor patio dinners in Brooklyn blew the air.

Gothamist reported that “residents of the critter Apple wants these unwanted tourists to skip town.”

WABC reinforced the pain of the city: “No, you are not ‘eavesdropping’. A swarm of insects seems to have taken over the city.”

But for every casual street reference to a biblical-style plague, whether it’s a swarm of locusts or mosquitoes or hail and thunder, there’s a scientist.

Dr. Corrie Moreau, a professor of entomology at Cornell University, who looked at images of the insects, which can be green or white, said she believed they were aphids trying to mate.

Insect swarms often form to coordinate reproduction, which she says can be attributed to its current appearance in New York City.

“It’s unusual to have so many of these aphids swarming this year,” she said. “It’s because of the mild winter.”

Aphids are a non-stinging insect that normally suck sap from plants. They are generally wingless, but appear winged in spring and fall.

The mild winter and rainy spring have made aphids optimistic about reproduction. Moisture means flowers and plants, a sign for them to go into reproductive mode in swarms, increasing the potential gene pool.

“It increases the likelihood that they will be very successful,” said Dr. Moreau.

Doug Currie, the senior curator of entomology at the Royal Ontario Museum, said he had never heard of similar swarms in Canada.

“Believe me, the Canadian media would contact me,” he said.

His most memorable aphid swarm in Canada was in 2001, when soybean aphids gathered so heavily around the lights of a stadium, then known as the SkyDome, that the Toronto Blue Jays game against the Baltimore Orioles was interrupted in the third inning.

“That’s why they closed the roof to get the game going again,” he said.

But in New York, there may be a thin connection between the aphids and the overhanging smoke.

“I think the smoke enhances our ability to see them properly,” said Dr. Moreau. “Because I can’t see that far, I tend to focus on things that are closer.”

Aphids are unlikely to be harmful if accidentally ingested, which some city types say is a concern if they walk down the street with their jaws open. So forget about the “bug” pollution. It’s the smoke you have to worry about.

“There have been plenty of Manhattan residents who have cycled. These are not toxic in any way,” said Dr. Moreau. “They should be wearing masks anyway, because of the air quality.”