The "butterfly effect" is used to explain a piece of Chaos Theory. It's meant to present the idea that events are entirely dependent on their initial conditions. Essentially it comes down to the idea that something as simple as a butterfly flapping it's wings could have a far-reaching ripple effect on subsequent events. So much so, that it might be able to ultimately accelerate, alter the path of, delay, or prevent a tornado. The flapping wing represents a small change in the initial condition of the system, which causes a chain of events leading to large-scale alterations of subsequent events.
I had wanted to do a graphic based on this for a long time, but finally forced myself to take the time to do it. I used a luna moth as the general shape and just kept plugging in other things until it filled up. Not an easy one.