Honeybees can be trained to locate landmines with an accuracy of better than 97.5%. Tracking them with laser-based radar could provide a fast and effective means of clearing the world’s minefields.
Landmines kill and maim tens of thousands civilians a year, 30–40% of whom are children. Moreover, although it costs only a few dollars to lay a landmine, it can cost many hundreds of dollars to find and remove it. Faster and cheaper methods for clearing minefields are desperately needed. Writing in Optics Express, Joseph Shaw and colleagues1 report progress in the use of lidar — a detection and ranging technique similar to radar that uses laser light instead of radio waves — to locate the position of honeybees that have been trained to find explosives buried in a minefield.
Landmines leak trace amounts of explosive chemicals into the soil and air around them. The ability of sniffer-dogs to distinguish such chemical signatures at concentrations down to one part per trillion and below, provides one means of locating buried mines. But it’s costly and time-consuming to train the dogs, and their potential to inadvertently trigger a mine while conducting a search puts them and their handlers at significant risk. In contrast, recent work by the same group2 suggests that honeybees — which posses a similarly sensitive sense of smell to that of dogs — could be just as effective at locating mines, but at lower cost, in greater number, and with minimal danger.
Honeybees can be trained to seek out a given chemical by adding it to their syrup feed. This encourages the bees to form an association between the scent of the chemical and a source of food, which in turn causes them to fly towards and around any source of that chemical that they find in their natural foraging behaviour. To take advantage of the bees’ mine-finding talent, it is vital to be able to locate them remotely.
To track the movement of bees over a minefield, Shaw and colleagues have developed a scanning lidar system based on one that had previously been designed to locate fish. The authors’ system consists of a pulsed laser mounted beside a photomultiplier tube, both of which are scanned horizontally back and forth across the field in question. Individual bees are located by synchronizing the detection of scattered light with the timing of the emitted laser pulses and the position of the scanned beam. By detecting where many bees congregate over time, Shaw et al. are able to map the location of active (but unfused) mines in a 44×24 m field at a distance of 83 m.