Phenotypic plasticity refers to the ability of a genotype to develop into different phenotypes in response to environmental cues. In many instances, this ability is an evolved adaptation to enable organisms to adapt to predictable but variable environments in time or space (West-Eberhard MJ, Developmental plasticity and evolution. Oxford Unversity Press, New York, p 794, 2003; Stearns SC, BioScience 39 (7) Here I provide a review of the literature that has explored how environmental variation, in particular seasonal variation, impacts eyespot size in African satyrid butterflies of the genus Bicyclus. Plasticity in eyespot size is undeniably the most conspicuous effect of seasonal variation on the appearance of Bicyclus species, and perhaps because of this, its ecological and physiological bases have been under investigation since 1984 (Brakefield PM, Reitsma N, Ecol Entomol 16:291-303, 1991; Brakefield PM, Larsen TB, Biol J Linn Soc 22:1-12, 1984). Much subsequent research on members of this genus, and in particular on the model species Bicyclus anynana, uncovered, however, many other morphological, behavioral, physiological, and life history traits that are equally impacted by seasons and, in particular, by rearing temperature (Bear A,