Space-Eater

"As for the droning that we heard and the shape we thought we saw above the burning forest—that was the horror seeking to make itself felt, seeking to break down barriers, seeking to enter our brains and clothe itself with our thoughts. It almost got us. If we had seen the white arm, we should have been lost."

- Howard, explaining what he and Frank had seen.

The "Space-Eaters" are a type of higher-dimensional alien life which has been present on planet Earth for millennia, and feed upon the brains of human victims. Under ordinary circumstances, their actual form and color are too eldritch to be perceived by human senses. Once one is able to assign a definite shape to them, it is a sign that the alien has already taken up residence within the victim's brain and is manifesting itself within their conscious thoughts.

Biology
For unclear reasons, the Space-Eaters have shown an affinity towards trees, and usually dwell in parks and forested areas. They're also associated with dense fogs and droning sounds, both of which often signal their nearby presence. They consume brains; possibly to extract knowledge from them. An indescribable sensation and agonizing pain are felt by the victim, as the unseen creature bores its way into their head to reach up and take residence in their brain. People who manage to survive an encounter with them may be found with deep wounds on their heads, as if they had been shot; except that the wounds are clean and parts of the victim's brains are inexplicably missing. Repeated attacks may leave the victim acting in an animalistic manner, entirely devoid of reason. At this point the victim is hopelessly doomed, as the parasite has already taken over what's left of their brains. A doctor who tried to operate on a man in such condition was left in a state of shock because of what he saw when he peeked inside the patient's wound.

Victims have also described seeing things that appear as long, white, thin arms, complete with hand-like extremities, coming from the trees. Although these structures resemble arms, they are impossibly thin, and have also been linked to something like a wire or string. It has been explained that the vision of such things is actually caused by the infected victim trying to interpret what they're seeing. As Howard put it: "of course Wells didn't really see the arm objectively, but the horror that is without form or color had already entered his brain and clothed itself in human thought".

In extreme circumstances (as seen when the woods were burning in flames), the Space-Eaters may also appear as a vast, formless shape moving over the tree tops across the sky; accompanied by a droning noise. Under these circumstances, one is advised to not look and to "pray that it remains without form"; otherwise it would mean that the alien presence is already inside one's mind.

The sign of the cross is the only thing that can repel these creatures; speculated to have been used since primordial times by mankind to fight back against the dimensional invaders.

Appearances

 * "The Space-Eaters", by Frank Belknap Long (1928)
 * Monsters, s03e15, "The Space-Eaters" (1991)