A few butterflies and many moth species spin a silk case or cocoon prior to pupating, while others do not, instead going underground. A butterfly pupa, called a chrysalis, has a hard skin, usually with no cocoon.
4. tension - (physics) a stress that produces an elongation of an elastic physical body; the direction of maximum tension moves asymptotically toward the direction of the shear. natural philosophy, physics-the science of matter and energy and their interactions; his favorite subject was physics.
Muscle tension is the feeling that muscles are always tight or strained, sometimes to the point of frequent pain, or even persistent and ongoing pain. One can experience tension, pain or cramps in any of the body's muscles as a result of muscle tension. The common symptoms of muscle tension are listed on the right.