The Sandia researchers announced last year that they had been testing bees' ability to detect mines. There are about 120 million land mines strewn around the world.

Because bees have statically charged bodies they pick up explosive particles just as they collect pollen, but the amounts are small, which makes analysis difficult.

In a separate project the same team had been developing tiny nanospheres with extensive networks of pores that trap particles and concentrate the amount of explosives up to 500 times.

"Already having the spheres, the idea came that they could be like artificial pollen," says team leader Jeffrey Brinker.

So the researchers began sending out bees with the nanospheres to turn them into more sensitive detectors. Early tests have been promising, and the team will get to work again once their hive emerges from hibernation in about a month's time.

Because various molecules can be built into the spheres, Brinker says the next step will be to create spheres that indicate the presence of explosives chemically, for example by changing colour.

Other possibilities include using spheres to detect biological weapons. "All these things are cooking along," says Brinker.

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