Females lay eggs on the host plant in late July and early August. After a few days, the tiny caterpillar crawls at the bottom of the egg into the ovary of the plant. The caterpillar will eat for ten days and thus start a growth spurt.
Once the caterpillar is 3–4 mm long, it drills a hole to crawl out of the flower and drop to the ground, right next to the host plant. The caterpillar is a master of chemical disguise and imitates the smell of the ant larvae. The ants of the genus Myrmica are not aware of any harm and think that one of their larvae has fallen out of the ant nest and urgently needs to be brought back inside.
When the caterpillar is in the ant nest, they feed the caterpillar as if it were one of their own ant larvae from autumn to the following spring with prey (e.g. other insects) that they collect outside the nest. As soon as pupation approaches around end of June - beginning of July, the caterpillar crawls to the top chamber of the ant nest where it pupates and later emerges from the chrysalis.
Haste is required because the butterfly no longer resembles an ant larva and must escape quickly before the betrayal is discovered and the ants see juicy prey in the emerging butterfly.

The larva lives on Gentiana pneumonanthe and is attended by ants of the genus Myrmica.