There was a short-lived cartoon called Sectaurs in 1984 that got me thinking about what the proper way is to map people onto flies. I was quite fond of the action figures. Basically, an accident causes a kind of half human, half-fly creature to emerge. For some reason, the shock of this idea really caught my imagination at age 9. I still remember thinking some of this through on the long school bus ride home.One of the first things I realized about it was that the concept of "average" I had been taught was the wrong way to go about finding out the height and weight of the monster. Suppose a person is 100x as big as a fly. Then the monster, I reasoned, should be 10x as big as a fly, and 10x as small as a person. The concept I was groping towards was the geometric mean.
Later, as I learned more about evolutionary development (as a kid I also found pictures of fetal development fascinating and grotesque in exactly the same sort of way as crossing people with bugs) I learned that the eyes of a human are not developed from the same part of the embryo as the compound eyes of a fly. Human eyes are, morphologically speaking, an extension of part of the brain. Fly eyes, on the other hand, have more to do with skin and hair cells.
The other interesting fact from evolutionary development I learned more recently. In humans, our spinal column is in our back. In insects, it runs down the belly. But they are caused by the same sets of genes at the beginning stages of embryonic development. Basically, the vertebrate body plan and the insect body plan are upside down from each other: our backs are their bellies. I can't see how including these facts in the next remake of The Fly would make it any less successful at being a horror movie!
Here's a reference for that last bit about the dorsal/ventral flip.