: Because they're wearing human skins.
That's what I first thought as well. However, they're wearing human skins, not whole human bodies. How much blood is going to be left in a human skin after it's removed from its original owner?
On a related issue, what is the evidence that the Fetch are purely electrical beings? Based on the fact that they seem to spurt a lot of blood when you hit them, I contend that they are really flesh and blood, but that their form is still so alien that they wear the skins of human beings. Alternately, "wearing the skins of men" could be a metaphor for altering their appearance to assume the shape of humans. Whether this is because they have to or not is still an open question, IMO. Doesn't the unit flavour for Myth II saying that they wear skins out of necessity appear in quotation marks? When I first read that, I got the impression that it was some religious Journeyman who was really little more than conjecturing.
Thanks,
Wasp