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. noun, Physics. 1. the elasticlike force existing in the surface of a body, especially a liquid, tending to minimize the area of the surface, caused by asymmetries in the intermolecular forces between surface molecules.