Reuters reports that bees have been sucessfully trained to smell out explosives:

By exposing the insects to the odor of explosives followed by a sugar water reward, researchers said they trained bees to recognize substances ranging from dynamite and C-4 plastic explosives to the Howitzer propellant grains used in improvised explosive devices in Iraq.

“When bees detect the presence of explosives, they simply stick their proboscis out,” research scientist Tim Haarmann told Reuters in a telephone interview. “You don’t have to be an expert in animal behavior to understand it as there is no ambiguity.”

If you have to get close enough to see their proboscis sticking out, you might be too close to the bomb to do much about it.

Now if they could just be trained not to get so angry and sting. Or, alternatively, maybe they could be used to swarm and attack anything that smells like a bomb. Imagine stopping a suicide bomber in his/her tracks by covering them with attack bees.

EDITED TO ADD (06 Dec 2006): Curiosity was getting the better of me so I found a source that describes how bee communication can be interpreted by humans from a distance. An optics.org report from August 2005 explains that trained bees will alter their behavior when flying over landmines, which can be detected by horizontal LIDAR:

The co-polarised LIDAR system uses a frequency-doubled 532 nm Nd:YAG emitting 100 mJ pulses at a repetition rate of 30 Hz. The back-scattered light is passed through a receiver with a linear polarisation parallel to that of the emitted light.

To test the feasibility of the approach, the team carried out an experiment on a live mine field. Using tens of thousands of bees, the researchers conclude that the scanning LIDAR consistently detected a higher bee density near most of the significant chemical plumes. But there is still a lot of work to do.

[…]

“The primary limitation was identifying bee-specific signatures from grass and other interfering objects,” said Shaw.

I love the details in optics.org. Ok, so let’s say that bees would be flying around checkpoints with LIDAR sensors. Could anyone stung by a bee, or that bees hover by, be reasonably assumed to have trace amounts of explosives? Not only does this present a very interesting partnership with nature and science, but imagine all the side benefits like military checkpoints planting flowers and selling honey on the side.