A grasshopper swarm in the Las Vegas Valley of Nevada has been so thick at times that the National Weather Service warned motorists it could impact visibility on area roads.

The swarm has been showing up in recent days in Sin City and at times has had the pallid-winged creatures raining down on streets and rooftops.

State entomologist Jeff Knight said in a news conference Friday the grasshopper population was likely nourished by the Southwest's relatively wet winter and spring. He said the insects are relatively harmless and will likely stay for a few more weeks before continuing to migrate north.

The grasshoppers seem to especially attract notice at night, Allen Gibbs, a life sciences professor at University of Nevada, Las Vegas, told NBC News affiliate KSNV.

“They’re used to a light level, say, moonlight," he said.

On Friday federal forecasters in the Las Vegas area warned motorists to beware. "Watch for areas of blowing dust and grasshoppers which may limit visibility," NWS Las Vegas said on Twitter.

The swarms have been so prominent, the agency stated, that they are likely showing up on weather radar.