Type species: Formica umbrata Nylander
More subterranean than the subgenus Lasius, some build large earthen mounds.
Mostly honeydew derived from subterranean plant lice and mealybugs.
"Workers are mainly yellowish and rarely seen above ground. These are parasitic species, whose young queens ... don't found new colonies of their own. Instead, they try to overtake colonies of other Lasius species (like L. neoniger) after overwintering. Indeed, the name Chthonolasius means 'killer' Lasius." [comment by Richard Vernier]