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 Definition. Muscle tension refers to the condition in which muscles of the body remain semi-contracted for an extended period. Muscle tension is typically caused by the physiological effects of stress and can lead to episodes of back pain. Stress may change the body's nervous system by constricting blood vessels and reducing blood flow to the soft tissues, including muscles, tendons, and nerves in the back.