Creatures from HP Lovecraft's scifi short story, In the Walls of Eryx.
The farnoth fly and ugrat were actually named by Lovecraft after personal adversaries of his.
This is part of a series of illustrations and concept work I plan to pursue about the short story, which has interesting similarities to Cameron's Avatar; namely that of mining groups going to a tropical alien planet (in this case Venus) where you'll die after breathing the air for a few minutes and the mining group's trying to mine for stones that power earth cities but are continually thwarted by pesky tribal natives. The main difference is these natives aren't sexy nine-foot tall humanoids but giant, tentacular lizard-like things.
Here's an earlier study of the lizardmen, with a slightly deviated skull morphology: