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.
surface tension. n. 1. A property of liquids arising from unbalanced molecular cohesive forces at or near the surface, as a result of which the surface tends to contract and exhibit properties resembling those of a stretched elastic membrane.