MULHOUSE, France (Reuters) - Bees at a cluster of apiaries in northeastern France have been producing honey in mysterious shades of blue and green, alarming their keepers who now believe residue from containers of M&M's candy processed at a nearby biogas plant is the cause.

Since August, beekeepers around the town of Ribeauville in the region of Alsace have seen bees returning to their hives carrying unidentified colorful substances that have turned their honey unnatural shades.


A coloured honeycomb from a beehive …


Mystified, the beekeepers embarked on an investigation and discovered that a biogas plant (2.5 miles) away has been processing waste from a Mars plant producing M&M's, bite-sized candies in bright red, blue, green, yellow and brown shells.

"We discovered the problem at the same time they did. We quickly put in place a procedure to stop it," Philippe Meinrad, co-manager of the biogas plant, he said the company had cleaned its containers and incoming waste would now be stored in a covered hall.

As for the M&M's-infused honey, it might taste like honey, but there the comparison stopped.

"For us, it's not honey. It's not sellable."