Quantum weather butterflies
These butterflies (Papilio tempestae) have wings of an undistinguished yellow with black mandelbrot patterns, and fractal edges of infinite length. A quantum weather butterfly can "create weather" merely by flapping its wings. It is possible that this is a sexual characteristic, that a male quantum weather butterfly will flap its wings and create, perhaps, a freak gale a few miles off, to show off its powers so to court a female quantum weather butterfly. Also, a quantum weather butterfly can make a small thunderstorm (usually about six inches across) over, for example, the head of a bird that is trying to eat this butterfly, so the butterfly can flee the place and the bird might remember not to pursue such butterflies another time.
The major appearance of the quantum weather butterflies is in Interesting Times, when the Lady uses a seemingly endless flock of them to create a storm over Hunghung and the plains around it, on the Counterweight continent.
The concept of the quantum weather butterfly is a parody, or a physical manifestation of metaphor (as so many others on the Discworld), of the "butterfly effect", of the chaos theory school of thought, that "the flapping of the wings of a butterfly may create a storm". (More accurately, the term was coined when Edward Lorenz discovered that minor changes in the initial condition of a weather simulation caused its outcome to differ greatly: "One meteorologist remarked that if the theory were correct, one flap of a seagull's wings could change the course of weather forever.")