After he and his girlfriend were swarmed by fire ants one day, writer Justin Nobel set off to figure out how they got to the U.S. and why they’re spreading farther north each year. Also in this show: In a patch of eastern Ecuador's Amazon rain forest, a researcher has been looking for treehopper insects that communicate using sound; and we have another nice piece from the Memory Palace, this one on what inspired one man to invent the telegraph.