Thousands of dead bees have been found in an Oregon parking lot.  25,000 bees died in the largest known incident of bumble bee deaths to date. Pesticides may be at fault.

The dead bees were "raining from the trees", witnesses said. The 25,000 bees died in a Target parking lot in Wilsonville, OR.

Initial investigations point to the death of the bumblebees being possibly due to pesticides in the trees above them, said the Xerces Society, an Oregon environmental organization.

"I've never seen an incident on this scale," said Mace Vaughan, pollinator conservation program director for The Xerces Society. ,

"When I was here Monday, it was even more dramatic than it is today," Hatfield told press. "There were bees raining out of trees."

Bees fell from the trees, wriggling on their backs or writhing on the asphalt. Some honeybees and ladybugs were also found. Bees clung to trees and scattered around the lot in piles.

Initial findings say that the trees were sprayed with a pesticide called Safari. Tests are being conducted. Nets may be used to protect the trees.

Bees have been dying rapidly in the U.S. since 2005, and researchers are not sure why.  It may be due to a new kind of insecticide that reduces bees' ability to learn scents, making it hard for them to find food.

About a third of beekeepers in the U.S. lost their colonies last year alone in the epidemic, dubbed "colony collapse disorder".

Colony collapse disorder means there are many less bees to pollinate crops nationwide. Bees are critical to agriculture.

"[The dead bees found in the parking lot] brings it home," Hatfield said, "that we've got a lot of work to do to learn how to not harm these insects that are critical to our food supply."

The Xeres Society and the Oregon Department of Agriculture is currently working to determine the cause of the bees' death.