This is Phengaris Arion, or the Large Blue butterfly. As a caterpillar its behaviour is rather interesting as a metaphor

The caterpillar, red in colour, if fallen from its rope of silk, can become prey to scavenging red ants, whereupon it is ferried to their lair. It then proceeds to do something very curious - it protects itself from being devoured by the ants by mimicking the pheremonal scent and clicking sound of their queen, pretending to be one of them. The deceived ants cannot do enough for the grub, cleansing it from parasites and dirt and nourishing it. The ants get nothing in return, but they nurture and protect the caterpillar as one of their own.

It continues like this even as it forms into a chrysalis, but once it is ready to emerge, it stops pretending to be an ant and stops emitting these pheromones. The butterfly, exposed, it has but one chance to escape from the lair of the ants, who remain unaware that they had been used and tricked like this.