Bees can detect target chemicals in the air in concentrations as low as a few parts per trillion. In tests, scientists were able to train bees to respond to the smell of the chemical components used to make explosives such as dynamite, C-4, and liquid bombs. The bees are trained to expect nectar after detecting the chemicals, and so start extending its tongue (proboscis) and waving in the air, searching for nectar.
By containing the bees in an enclosed structure, such as small tubes, researchers can use monitoring equipment (digital camera combined with pattern-recognition software) to alert to the waving of the proboscises, which would indicate the presence of explosives in the vicinity. The portable structure makes it ideal for testing in airports, subway stations and at roadside checkpoints.