The “Mi-go” are large, pinkish, fungoid, crustacean-like entities the size of a man; where a head would be, they have a “convoluted ellipsoid” composed of pyramided, fleshy rings and covered in antennae. According to two reports in the original short story, their bodies consist of a form of matter that does not occur naturally on Earth; for this reason, they do not register on ordinary photographic film. They are capable of going into suspended animation until softened and reheated by the sun or some other source of heat. They are about five feet (1.5 m) long, and their crustacean-like bodies bear numerous sets of paired appendages. They possess a pair of membranous bat-like wings which are used to fly through the “aether" of outer space (a scientific concept which is now discredited). The wings do not function well on Earth. Several other races in Lovecraft’s Mythos also have wings like these. (x)
"Something black in the road, something that wasn’t a tree. Something big and black and ropy, just squatting there, waiting, with ropy arms squirming and reaching… It came crawling up the hillside… and it was the black thing of my dreams – that black, ropy, slime jelly tree-thing out of the woods. It crawled up and it flowed up on its hoofs and mouths and snaky arms."
—Robert Bloch, “Notebook Found in a Deserted House”