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.
tension. n. 1. the act of stretching or the state or degree of being stretched. 2. mental or emotional strain; stress. 3. a situation or condition of hostility, suspense, or uneasiness. 4. (General Physics) physics a force that tends to produce an elongation of a body or structure. 5.