The Crawlers by Philip K. Dick

He built, and the more he built the more he enjoyed building. Hot sunlight filtered down; summer breezes stirred around him as he toiled joyfully. When he ran out of material he paused awhile and rested. His edifice wasn't large; it was more a practice model than the real thing. One part of his brain told him that, and another part thrilled with excitement and pride. It was at least large enough to enter. He crawled down the entrance tunnel and curled up inside in a contented heap.

Through a rent in the roof a few bits of dirt rained down. He oozed binder fluid and reinforced the weak place. In his edifice the air was clean and cool, almost dust-free. He crawled over the inner walls one last time, leaving a quick-drying coat of binder over everything. What else was needed? He was beginning to feel drowsy; in a moment he'd be asleep.

He thought about it, and then he extended a part of himself up through the still-open entrance. That part watched and listened warily, as the rest of him dozed off in a grateful slumber. He was peaceful and content, conscious that from a distance all that was visible was a light mound of dark clay. No one would notice it: no one would guess what lay beneath.

And if they did notice, he had methods of taking care of them.