NEW YORK (PIX11) — New York City seems to have been overtaken by a swarm of gnat-like insects, leaving people puzzled as to where the bugs came from.

New Yorkers have taken to Twitter to document the mob of insects buzzing through the air in subway stations, plazas, and bike paths. The bugs were spotted flying around in Manhattan and Brooklyn.

“These swarms of bugs are taking over the city. They are in the subway platform too. The city just keeps getting worse. What’s next?” one New Yorker tweeted, with a video depicting the horde.

Some folks report the bugs look white, while others say they are green.

The gnat-like insects aren’t actually gnats, according to American Museum of Natural History entomologist Dr. David Grimaldi. They are known as aphids, and there appears to be two species flying around, Grimaldi said.

“They may be native species or species that were introduced years ago (doubtfully recent),” Grimaldi told PIX11 News. “Every species goes through population cycles over the years, and this might be a boom year for them, with a mild spring and then the rains and humid warmth.”

“Also, for aphids in particular,” Grimaldi continued, “local populations of each species tend to be synchronized in their development from wingless to alate morphs (not unlike cicadas), and the transition to winged forms is what we’re seeing.”

Grimaldi said aphids feed on the fluids of plants, such as tree leaves. They excrete little droplets of sugary secretions which sustain ants and other insects.

“Given their numbers, these aphids are probably feeding from trees along sidewalks, in Central, Prospect, and other parks,” Grimaldi said.

Some people theorized that the swarms are appearing due to Canadian wildfire smoke blanketing New York City. However, Grimaldi said he didn’t know of any plausible connection between the aphids and wildfire smoke.

For those wondering how long the swarms of aphids will be around in New York City, Grimaldi said: “A lot depends on the weather. If temperatures remain mild and humidity and rainfall high, they will survive longer, for a few days to maybe a week or more.”

Grimaldi added that there are no health concerns related to the swarms of aphids.