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.
The surface contracts and results in surface tension. surface tension definition The tension in the surface is the force per unit length that must be applied parallel to the surface as to counterbalance the net inward pull Force per unit length existing at the interface between two immiscible liquids