Wired summarizes destructive methods usable by micro robots and micro UAVs
Israel is developing a robot the size of a hornet to attack terrorists. And although the prototype will not fly for three years, killer Micro Air Vehicles, or MAVs, are much closer than that.
British Special Forces already use 6-inch MAV aircraft called WASPs for reconnaissance in Afghanistan. The $3,000 WASP is operated with a Gameboy-style controller and is nearly silent, so it can get very close without being detected. A new development will reportedly see the WASP fitted with a C4 explosive warhead for kamikaze attacks on snipers. One newspaper dubbed it "The Talibanator."
A MAV could put a truck out of action by destroying its tires. A MAV can do this by squirting them with few milliliters of a catalytic de-polymerization agent, causing them to disintegrate rapidly. An entire command center can be disabled by targeting the power supply. The MAV could do this by physically crawling inside like a wayward squirrel, or it might release a cloud of metal-coated fibers -- similar to the "soft bombs" the Air Force used to shut down power stations in Kosovo with a cloud of conductive whiskers.
This pdf discusses the use of poisons and stingers on MAVs