The Forgotten Planet by Murray Leinster

They had food for days. They had brought mushroom from the isolated thicket not too far beneath the clouds. There were the ants that Dik and Tet had distributed grandly, and not all of which had been used to secure escape from the canyon of the millipede. Had they found other food immediately, they would have settled down comfortably in the fashion normal to creatures whose idea of bliss is a secure hiding-place and food on hand so they do not have to leave it. Somehow they believed that this high place of bright light and new colors was secure. But they had no hiding-place. And though they did accept with the unreasoning faith of children and savages that there were no enemies here, they still wanted one.

They found a cave. It was small, so that it would be crowded with all of them in it, but as it turned out, this was fortunate. At some time it had been occupied by some other creature, but the dirt which floored it had settled flat and showed no tracks. It retained faint traces of a smell which was unfamiliar but not unpleasing, -- it held no connotation of danger. Ants stank of formic acid plus the musky odor of their particular city. One could identify not only the kind of ant, but its home city, by sniffing at an ant-trail. Spiders had their own hair-raising odor. The smell of a praying-mantis was acrid, and all beetles reeked of decay. And of course there were those bugs whose main defense was an effluvium which tended to strangle all but the smell's happy possessor. This faint smell in the cave was different. The humans thought vaguely that it might possibly be another kind of man.