Caterpillars are Foolish Creatures to begin with. Apparently, they save up all of their ugliness for their first stage of life, and then stick with being glamorous butterflies after they leave their cocoons.
For the Large Blue Butterfly, the strangeness doesn't stop there. Apparently, as a caterpillar, the Large Blue Butterfly masks itself in the chemical scent of other ants, and then ensures that it gets escorted back into their hive. Once in the hive, the caterpillar blissfully starts munching away at everything in the nest, including the ants themselves. Over a period of about a year (two if the caterpillar rations its delicious ants), the caterpillar grows immensely, and then even spins its cocoon under the protection of the ant colony.
Finally, the Large Blue Butterfly emerges, leaving what's left of the colony to wonder what exactly just happened.
