What he saw descending from the black chasm weren't men. They were alien — from some other world, some other dimension. Sliding through this slit, this break in the shell of the universe. Entering through this gap, winged insects from another realm of being...

(Aliens/Stingers from 'The Hanging Stranger' by Philip K. Dick)

... The shape, the manshape, had abruptly fluttered up and flapped after the others. It flew to the sidewalk and came to rest among them.
Pseudo-men. Imitation men. Insects with ability to disguise themselves as men. Like other insects familiar to Earth. Protective coloration. Mimicry.

He heard the buzz. And dropped instantly, the long butcher knife out. Sickened, he saw it coming down the stairs at him, wings a blur of motion as it aimed itself. It still bore a vague resemblance to Jimmy. It was small, a baby one. A brief glimpse — the thing hurtling at him, cold, multi-lensed inhuman eyes. Wings, body still clothed in yellow T-shirt and jeans, the mimic outline still stamped on it. A strange half-turn of its body as it reached him. What was it doing?
A stinger.
Loyce stabbed wildly at it. It retreated, buzzing frantically. Loyce rolled and crawled toward the door. Tommy and Janet stood still as statues, faces blank. Watching without expression. Loyce stabbed again. This time the knife connected. The thing shrieked and faltered. It bounced against the wall and fluttered down.
Something lapped through his mind. A wall of force, energy, an alien mind, probing into him. He was suddenly paralyzed. The mind entered his own, touched against him briefly, shockingly. An utterly alien presence, settling over him — and then it flickered out as the thing collapsed in a broken heap on the rug.
It was dead. He turned it over with his foot. It was an insect, a fly of some kind. Yellow Tshirt, jeans.t