Common blue  (Polyommatus icarus)

Bivoltine: (also known as ‘double-brooded’). Insect life cycle that takes 12 months to be complete, but involves two generations in that time. The first generation adults lay eggs that give rise to those of the second generation. The second generation overwinters either as an egg, larva, pupa or adult.
Pupae: stage in an insect’s development when huge changes occur, which reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis.
Pupation: the process of becoming a pupa, the stage of an insect’s development, when huge changes occur that reorganise the larval form into the adult form. In butterflies the pupa is also called a chrysalis.
univoltine: (Also known as ‘single brooded’). Insect life cycle that takes 12 months to be complete, and involves a single generation. The egg, larva, pupa or adult over winters as a dormant stage.

1. National Biodiversity Network Species Dictionary (September 2003):
   http://www.nhm.ac.uk/nbn
   
2. Carter, D. (1992) Butterflies and moths. Dorling Kindersley, London.
   
3. Carter, D. & Hargreaves, B. (1986) A field guide to caterpillars of butterflies and moths in Britain and Europe. William Collins & Sons Ltd, London.
   
4. Asher, J., Warren, M., Fox, R., Harding, P., Jeffcoate, G. & Jeffcoate, S. (2001) The Millennium Atlas of Butterflies in Britain and Ireland. Oxford University Press, Oxford.
   
5. Still, J. (1996) Collins Wild Guide: butterflies and moths of Britain and Europe. Harper Collins Publishers, London.