The invasive pest Asian giant hornets have been spotted in the United States for the first time, scientists say.

Beekeepers in Washington state have reported piles of dead bees with their heads ripped off, an alarming sight in a country with a rapidly declining bee population.

At more than two inches long, they're the world's largest hornets with a sting that can kill humans if stung multiple times, according to experts at the Washington State University. The giant insects are nicknamed "murder hornets."

"They're like something out of a monster cartoon with this huge yellow-orange face," Susan Cobey, a bee breeder at the Washington State University's department of entomology, said recently, according to CNN.

The Asian giant hornet was first spotted in the state in December, and scientists believe it started becoming active again last month, when queens emerge from hibernation to build nests and form colonies.

"Hornets are most destructive in the late summer and early fall, when they are on the hunt for sources of protein to raise next year's queens," Truscott said on the WSU's Insider.

"They attack honey bee hives, killing adult bees and devouring bee larvae and pupae, while aggressively defending the occupied colony," he added. "Their stings are big and painful, with a potent neurotoxin. Multiple stings can kill humans, even if they are not allergic."

Washington state agricultural officials are asking beekeepers and residents to report any sightings of the Asian giant hornets. But don't get too close. Its sting can penetrate a regular beekeeper's suit, and state scientists had to order special reinforced suits.

"Don't try to take them out yourself if you see them," said entomologist Chris Looney of the state Department of Agriculture. "If you get into them, run away, then call us! It is really important for us to know of every sighting, if we're going to have any hope of eradication."

State officials are asking people in Whatcom, Skagit, Island, San Juan, Jefferson and Clallam counties to be especially vigilant.