Extended Four-Bug Problem
This Demonstration extends the four-bug problem in several ways. Consider bugs placed equally on the circumference of a circle. With each step, each bug takes one step closer to its anticlockwise neighbor. You can vary the the number of bugs, the step length and the number of steps. Also, the bugs are locators that you can drag. If you move the locators, do not change their sequential order.
 M. Gardner, "Mathematical Games: Nine Titillating Puzzles, the Answers to which Will Be Given Next Month," Scientific American, 197(5), 1957 pp. 140–146.