Michel Costa had become a frustrated veteran of an obscure yet devastating war in Europe. The enemy: invasive Asian hornets, which had been massacring his honey bees. When Costa, a retiree and avid beekeeper, discovered a new weapon with the potential to change the course of the entire war, he was intrigued. Several companies had begun selling so-called "electric harps," which they claimed could kill the hornets in droves by electrocuting them as they flew through. Although the harps take different forms, each one is made of some sort of large frame, which is then "strung" with conductive metal wires. These are then connected to a source of electricity, often solar panels, so that the wires conduct simultaneously positive and negative charges. When a hornet flies through, its wings touch the wires on either side, completing a circuit, and thereby delivering a fatal current of electricity. Beekeepers then place the harps around their hives in positions along the hornets' frequent flight paths. The harps can reduce predation pressure by 89 percent " enough to give hives the chance to replenish their stores. In one study only 56 percent of unprotected hives survived through winter, while 78 percent of those protected by harps did. Harps are also cheaper than other methods for beekeepers to install and operate. Beekeepers can buy them in complete kits that cost around $300 ... as Costa did. When combined with solar panels, maintenance costs are minimal.