The Apollo butterfly shows a great deal of individual variation in the appearance, with an evident colour polymorphism.

[8] The wings are shiny, with slightly transparent edges;[9] some individuals are darker (sphragismelanistic), a general phenomenon common in many butterflies.

[10] The drastic climate change of the Pleistocene era forced a separation of the red Apollo butterfly population.

Still within these isolated populations the butterflies migrated westward into portions of southern Europe where they settled and reproduced.

It is said that the red Apollo is an "atypical glacial invader" and that with the warming of the climate in mountainous regions is causing the butterfly to not readily adapt to such an uncomfortable environment.

This is because the outcrop of the nectar plants are the sight of reproduction and if the spatial structure is too far for the butterfly to migrate to the dynamics of the population is in danger.

[3][7] When the caterpillar is fully grown it will pupate on the ground, forming a loose cocoon from which the adult butterfly emerges following metamorphosis.

A common predator, nesting water pipits, have evolved a strategy to avoid the poor taste of the butterfly; the bird will remove the wings before consuming the body.

While over-collecting is believed to have caused populations to decline in some areas, such as in Spain and Italy, habitat change is thought to be a far more significant threat to this species' survival.

In Sweden, it is now restricted to areas that have limestone in the ground, suggesting that the decrease could hypothetically be related to acid rain.

It was the first butterfly to be protected by law; the German Emperor Wilhelm I leading efforts to secure the species.

[19] The Apollo is on the IUCN Red List of Threatened Species,[1] in Appendix II in CITES,[2] and is mentioned in annex IV of Habitats Directive.

However, these laws focus on the protection of individuals, rather than their habitat, and so may do little to mitigate the greatest threat that populations face.

A conservation programme in Pieniny National Park saved a subspecies of the Apollo butterfly that had declined to just 20 individuals in the early 1990s, through a combination of captive breeding and habitat protection.

[20] In south-west Germany, conservationists are working with shepherds to ensure favourable conditions for the butterflies, which share their grassland habitat with sheep.

For example, grazing periods have been shifted to avoid the Apollo butterfly larvae stage, which is vulnerable to being trampled.

This is mainly caused by habitat destruction, air pollution affecting the insect's food plants, and butterfly collectors.

This article incorporates text from the ARKive fact-file "Apollo butterfly" under the Creative Commons Attribution-ShareAlike 3.0 Unported License and the GFDL.