Dia da Morte
Este é DeathDay por William Dietz. Sua sequela é EarthRise .
O detalhe mais notável é confirmado por TV Tropes :
In the Deathday and Earthrise duology, Earth is invaded by an alien race known as the Saurons. The Saurons have a Fantastic Caste System based on scale color: black-scaled Saurons (Zin) are the ruling class, brown-scaled (Kan) are the soldiers, and white-scaled (Fon) are the laborers. When the Saurons enslave humanity, they treat darker-skinned humans much better than white-skinned humans as a result, which sets the stage for racial strife among the humans even as they try to overthrow the Saurons.
A nota da Amazon a aparição do insectoide dos Sauron:
The huge, insect-like Saurons, nicknamed "chits" for their chitinous shells, kill billions.
Quanto às outras espécies, cito esta resposta :
The next closest example I can think of is William Dietz’s DeathDay/EarthRise duology (2001) which chronicles the invasion of Earth by Saurons aided by the Ra ‘Na, who are a slave race to the Saurons (the ‘pets’ are actively involved in the invasion, rather than being brought in later).