Mexican jumping beans' jumping ability is not caused by the beans themselves. Instead it's an insect called the bean moth (Carpocapa saltitans) that creates this phenomenon. The moth lays its eggs around a bean flower or in the seed pod of the spurge. Then the egg will hatch within the shell and a caterpillar or larva will be living within the shell. Then, when the bean is exposed to heat, such as the heat of your hand, the insect will start to become annoyed and begin moving.