Rajah Brooke’s birdwing was named after the White Rajah of Sarawak, Captain Brooke, who ruled an English Province in northern Borneo in the middle of the 19th century (3). It is a striking species which gathers in groups of up to 80 individuals to drink from puddles. Newly emerged males must absorb mineralised water containing the sodium and potassium ions necessary to activate adult behaviour. Holding the wings in a V-shape, the butterflies drink and squirt the excess water from the abdomen in small jets or droplets. Rajah Brooke’s butterfly also drinks nectar from Bauhinia plant species (2).
It was previously thought that the sex ratio of this species favoured males, as females are rarely encountered, but there are now known to be equal numbers of males and females, although females are secretive and elusive. Courtship takes place in flight and the male will chase the female as she dives to evade him. If she accepts his advances, they will mate in flight; however, she may reject him, displaying her intentions by lying with the wings flat on the ground and the abdomen pointing upwards. Some males do not court the females, instead ambushing them in order to mate. Once the female is ready to lay eggs, she flies slowly and erratically in search of a food-plant, identifying the correct plant species using taste-sensitive chemoreceptors on the forelegs. Up to 50 small, round, white eggs are laid on the plant, hatching to produce caterpillars that rapidly consume the leaves, before pupating. In the pupa, metamorphosis occurs before an adult butterfly emerges (2).