How did fleas adapt to parasitism?

The oral apparatus is adapted for tingling the skin and sucking blood
The wings are reduced
The body is flattened laterally to make it easier to move into the animal’s fur.
The head is rounded to make it easier to spread the coat
All outgrowths of the body – bristles, antennae, spines – are turned back so as not to interfere with movement among the hairs and there are corresponding depressions for everything on the flea’s body.
The segments go over each other, like a tile, smoothing the protrusions of the body
Hind legs are jumping