the Phengaris rebeli, in which there exist slow-developing larvae (SDL) (75% of the total P. rebeli larval population) and fast-developing larvae (FDL) (25% of the total P. rebeli larvae population). The slow-developing larvae do not grow much during the first year, but grow rapidly during the early part of the second summer and remain a second winter within the ant colonies. On the other hand, the FDL complete their growth the following spring after they are taken into the ant nest. Sexual dimorphism Sexual dimorphism is the occurrence of differences between males and females in a species. In Lepidoptera, sexual dimorphism is widespread and almost completely determined by genetic determination. Sexual dimorphism is present in all families of the Papilionoidea and more prominent in the Lycaenidae, Pieridae and certain taxa of the Nymphalidae. Apart from colour variation which may differ from slight to completely different colour-pattern combinations, secondary sexual characteristics may also be present. Different genotypes maintained by natural selection may also be expressed at the same time. Polymorphic and/or mimetic females occur in the case of some taxa in the Papilionidae primarily to obtain a level of protection not available to the male of their species. The most distinct case of sexual dimorphism is that of adult females of many Psychidae species who have only vestigial wings, legs, and mouthparts as compared to the adult males who are strong fliers with well-developed wings and feathery antennae. Geographical polymorphism Geographical polymorphism is where geographical isolation causes a divergence of a species into different morphs. A good example is the Indian white admiral (Limenitis procris) which has five forms, each geographically separated from the other by large mountain ranges. An even more dramatic showcase of geographical polymorphism is the Apollo butterfly (Parnassius apollo). Due to the Apollos living in small local populations, having no contact with each other, but because of the strong stenotopic species and weak migration ability interbreeding between populations of one species practically does not occur; they form over 600 different morphs, with the size of spots on the wings of which varies greatly. Environmental polymorphism Environmental polymorphism, where genetic heritability plays no role, is often termed as polyphenism. Polyphenism in Lepidoptera is commonly seen in the form of seasonal morphs especially in the butterfly families of Nymphalidae and Pieridae. An Old World pierid butterfly, the common grass yellow (Eurema hecabe) has a darker summer adult morph, triggered