D
David Gerrold
The War Against the Chtorr
Earth faces an alien invasion by the Chtorr, a rapidly evolving species that consumes all life. This series follows humanity's desperate struggle for survival against an enemy that adapts to every defense. It's a bleak military science fiction story about a war for the planet itself.
The series should be read in the order of publication, starting with A Matter for Men, followed by A Day for Damnation, A Rage for Revenge, and A Season for Slaughter.
A fifth book titled A Method for Madness exists, though it is often listed separately from the initial four-book sequence.