The answer to this question is that crane flies are insects that undergo complete metamorphosis.
The larvae of crane flies look like small, legless grubs with a brown or blackish color.
During the next stage of their development, they exist as a pupa - which is also called a "chrysalis" if it's butterfly or "cocoon" if it's moth. The pupa doesn't have any legs or wings and its head is usually hidden beneath its body.
Finally, the adult crane fly emerges from the pupa case through a hole in one end of it.