Simultaneously , a protective layer builds up and forms a cocoon , which aids in protection of the vital organs of the fly .
In this stage , there are many transformations that occur , such as the formation of legs , head , and wings .
, a protective layer builds up and forms a cocoon , which aids in protection of the vital organs of the fly .
In this stage , there are many transformations that occur , such as the formation of legs , head , and wings .