Grasshoppers have incredibly powerful legs that allow them to jump far distances when faced with danger. Tthe grasshopper's jumping ability is equivalent to a human leaping the distance of a football field or more.
When jumping, grasshoppers first bend their hind legs at the knee joint by contracting their big flexor muscles. Their knees contain a unique piece of cuticle that acts as a spring, releasing large amounts of stored energy. By relaxing their leg muscles, grasshoppers are catapulted through the air, ideally removing them from harm's way. Most grasshoppers have wings and are capable of flying, so their jumping skills aid them in taking off quickly.
Grasshoppers also use their legs to attract potential mates with courtship calls. Most grasshoppers rub their hind leg against their forewing to produce sounds – an act called stridulation. After mating with females, some grasshoppers ride on their backs for a day or more, in order to prevent them from mating with other potential partners.
Scientists believe that grasshoppers spit brown liquid to repel predators as a means of self-defense. Because of their association with the destruction of tobacco crops, the repellent liquid has been called "tobacco juice" due to its brown, tobacco-like color. However, there is no proof that the liquid is in any way related to tobacco crops.