Mobile animals cannot afford such structural freedom. You can see that members of every species follow a basic body pattern. Staying alive is a challenge for every organism. Self-Defense Running away is not the only defense against being eaten. Plants grow thorns and prickles, and animals may grow spines like porcupines, or armor, like crabs and insects.
Skunks use odor to protect themselves, and octipi hide themselves in dense clouds of ink.
Bees and wasps have stings, and many animals can bite. Some animals hide, or take refuge in burrows in the ground. Another form of self defense is protective coloration, which allows an organism to become nearly invisible by blending into its surroundings. Many plants, and some animals, reproduce and grow so quickly that their species can survive even if individuals have short lives. Another problem is dealing with interruption of essential needs.