For those who are interesting some information from Wikipedia: The ♀ lays eggs singly on the flowerheads of Cuckoo Flower, Garlic Mustard and other species of wild crucifers, all of which contain chemicals called glucosinolates. Selection of foodplants is triggered by the presence of mustard oils and their derivative glucosinolates, which (in Pierinae) are detected by chemosensory hairs on the fore-legs. Reproductive rate of ♀♀ appears to be limited by difficulties in finding suitable hosts. As a consequence, the species has evolved to use a wide range of crucifers.
The eggs are white to begin with but change to a bright orange after a few days before darkening off just before hatching. Because the larvae feed almost exclusively on the flowers and developing seedpods there is rarely enough food to support more than one larva per plant. If two larvae meet one will often be eaten by the other to eliminate its competitor. Newly hatched larvae will also eat unhatched eggs for the same reason. To stop eggs from being laid on plants already laid on the ♀ leaves a pheromone to deter future ♀♀ from laying. The green and white caterpillar is attacked by several natural enemies (notably Tachinid flies and Braconid wasps). Pupation occurs in early summer in scrubby vegetation near the foodplant, where they stay to emerge the following spring. Recent research suggests that the emergence of the butterfly may be delayed for as much as two years, thus insuring the species against unfavorable conditions in a given season.
* Canon EOS 5D Mark II, 100mm/f2.8; ISO-400, f6.3, 1/250s; -0.3 stop, hand held.
