Harvard's Robobees are already pretty adroit for paper-clip sized drones; they fly around stably in calm air and hover like real bees (if real bees were tethered to power). Researchers have given them a new talent that even the insects don't have -- the ability to "fly" underwater. To do so, they make like ducks and transition from flight to swimming by crashing into the water, sinking a bit, then flapping their wings at a slower pace (9 Hz) than in the air (120 Hz) . That's already a feat that few drones can match, but the aim is to eventually build autonomous bots that could do search and rescue and other beneficial activities.
The team performed the feat sans any hardware modifications, though there are a few caveats. As mentioned, there still aren't tiny batteries powerful enough to let the bees soar on their own power (yet). That's because the smaller a drone is, the less flight endurance it generally has -- and at 100-milligrams (0.004 oz) Harvard's Robobees are pretty small. Also, the team needed to lubricate the wings, otherwise it's too light to break the surface tension and transition to swimming. The drone also needs extra energy to break free of the water, and flies badly for the first few moments afterwards due to water on the wings.
Harvard's scientists still need to sort those issues and others that don't phase real bees, like flying in a stiff wind. Once that happens, however, there will be no place that's safe from them on land or sea.