The wonders of butterfly metamorphosis are well-known to many people. The Brenton Blue is a particularly interesting member of the Lycaenid family. Like many of the species in this family, the Brenton Blue is myrmecophilous. This means that, during some stages of their lifecycle, they have a strong association with a particular species of ant. The Brenton Blue lifecycle occurs twice in every year.

This plant is called Indigo (scientific name Indigofera erecta), a member of the legume (pea) family, with small, pink flowers that look like miniature sweet peas.
In November and February, Brenton blue butterflies begin life as an egg, carefully laid on a leaf of their food plant. A tiny caterpillar emerges from this egg ten days later and begins to feed on the leaves, growing with every mouthful. The caterpillar is covered in tiny hairs and is now called the "first instar".
Male butterflies set up territories to attract females. After mating, the female lays her eggs on the leaves of the foodplant, and the whole cycle begins again. As the caterpillar grows, it sheds its skin (moults) twice, reaching the stage known as the "third instar". It is now about 10 days after hatching and crawls down the stems of the plant, to seek out members of the ant species, Camponotus baynei. It depends on these ants for food and protection.
The adult butterfly emerges about 10 days later (late October and November). The caterpillar attracts the ants by secreting pheromones, which prompt the ants to protect and feed the caterpillar, rather than attack it. The ants protect and nurture the butterfly larva and, in return, receive a sweet substance from special honey glands on the caterpillar's skin.
The caterpillar spins a cocoon (chrysalis) around itself, attached to the root of the plant, and the process of becoming a butterfly (metamorphosis) begins. At this stage, the larva needs to feed on the roots of the plant and the ants help it by excavating a hole around the plant's roots. The caterpillar continues to grow, reaching the final stage, or "fourth instar". It is now about 40-50 days since hatching and the larva is 12-20mm long. The caterpillar is ready to pupate.