Lots of subsequent science fiction - most notably, Jack Finney's The Body Snatchers (1955), and four subsequent movie adaptations - picked up on aspects of this theme. And so has Falling Skies.
The twist with Falling Skies is that the insect aliens attach a mechanical-organic device to the backs of human children, which turn them into zombie slaves, and at this point result in the death of the carrier if the device is removed. One of Tom's sons has been so harnessed, and his burning desire to get back and free his son - which any parent would have - is one of the mainsprings of the plot.
A doc may have a way of removing the alien spine without killing the carrier, but the process is untested, and Tom has no love for the doc, given that the doc earlier left Tom's wife to die so the doc could escape. In one of the best lines of the episode, the doc says to Tom that the doc's survival at the expense of Tom's wife may be the factor enables Tom to get back and free his son, so Tom's wife may not have died in vain.
But this assumes that the doc's procedure actually works, and, as we see in the last scene, it may work but not in the way that we humans hoped ...
See also Falling Skies 1.1-2 ...
Special Discount Coupons for Angie's List, Avis, Budget Car, Garden.com, eMusic
The Plot to Save Socrates
"a Da Vinci-esque thriller" - New York Daily News
"Sierra Waters is sexy as hell" - curled up with a good book
And check out my short history of science fiction, from The History Channel -