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.
Strain is defined as to exert or stretch to the maximum or to injure by too much exertion. 1  An example of strain is for a spectator to stretch over his seat to see a concert. 2  An example of strain is for a football player to pull a muscle from playing too roughly.  to draw or stretch tight.