This is not a capability until we know how predictable it is

Dr Alan Rudolph, Pentagon researcher

One option under consideration is to place a trained hive near security checkpoints to raise the alert should a bomber try to cross.

Bees appear even better able than dogs to detect particular odours, and roam large distances from the hive in search of food.

Scientists already know that their behaviour can be conditioned by rewards such as sugar-water.

Combining the scent of the sugar solution with tiny residues of TNT means that bees associate the "molecular trail" of TNT with food.

When a bee carrying this information returns to the hive, it will pass the knowledge of the scent and its location to thousands of other bees.

High success rate

Pentagon scientists say they have already succeeded in persuading bees to swarm around explosives - even in preference to flowers.

The research team claims that after training, this happens 99% of the time.

Hives could be placed near to security checkpoints

They claim they can track the insects by attaching a tiny radio transmitter to certain individuals.

Bees have, if food is scarce, a range of up to three or four kilometres from the hive.

However, they have limitations, including being unwilling to go out of the hive at night, or during cold and stormy weather.

Dr Alan Rudolph, who is overseeing the programme, told the New York Times: "This is not a capability until we know how predictable it is."

Not so busy

A UK expert said that the plan was "feasible" - although it did have limitations.

Richard Jones, the director of the International Bee Research Association in Cardiff, Wales, told BBC News Online: "It's quite possible. You can train a bee.

If there is something else more tempting on offer, they will go for that instead

Richard Jones, International Bee Research Association

"If you put sugar-water outside your window at a certain time each morning, the bees will come back every day - but only at that time.

"So if you mixed the sugar-water with a hint of TNT, you would condition them to hunt for TNT.

"However, bees are pretty damn lazy, really. If there is something else more tempting on offer, they will go for that instead. They will go for the nearest source of food.