The mass death of more than 25,000 bumble bees in an Oregon shopping center parking lot has been disturbing enough that crews are now putting bee-proof netting around trees in an effort to prevent more deaths.

bumble bee death

This photo provided by the Xerces Society for Invertebrate Conservation shows some of the thousands of dead and dying bees found in the parking lot of a shopping center in Wilsonville, Ore., southwest of Portland. Oregon officials say their preliminary investigation indicates blooming trees in the lot were recently sprayed with an insecticide known to be toxic to bees. The pencil was placed in the frame by the source to show scale. (Photo: AP/The Xerces Society for Invertebrate Conservation)

What has been causing the insects’ demise near a Wilsonville Target store over the past week? So far, officials aren’t entirely sure.

The Oregonian reports that Agriculture officials are working with the Xerces Society, the city and the distributor of an insecticide to figure out the problem. State officials say tests to confirm the cause of the deaths could take two or three more days. They are checking for insecticides as well as possible natural causes.

“We’ve never seen anything like this, at this scale,” a man said in a Newsfix video about the event. Watch the clip:

At this point though, the dozens of linden trees around the Target parking lot are being covered in case any natural toxicity in the trees were a factor.

“We have to do this now and prevent any additional bumblebee loss,” Mace Vaughan, pollinator program director for the Xerces Society, told the Oregonian.

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The Associated Press contributed to this report. Featured image via Shutterstock.com