Pace Michael Behe and William Dembski, bacterial flagella are not irreducibly complex. Here is Ian Musgrave’s clear explanation, “Evolution of the Bacterial Flagellum.”
Dr. Musgrave points out, “The specification of “ an outboard motor,” which provided the IC [irreducibly complex] system description of motor, shaft, and propeller, is a flawed human analogy to the actual flagellar system.” He also points out that Behe’s own definition of irreducibly complex systems excludes flagella, whose original function was not motility but secretion. Dembski, by building on Behe’s flawed description, in my opinion goes further astray into “Why bumblebees can’t fly” territory.
There’s much more! Read the article.