While most butterfly species in the genus Polyommatus Latreille, 1804 (Lepidoptera, Lycaenidae) exhibit strong sexual dimorphism, several species in the subgenus Agrodiaetus Hübner, 1822 are monomorphic, with males and females having a similar brown coloration. It is also known that this monomorphic complex of Agrodiaetus butterflies consists of morphologically very similar cryptic species that are almost identical in coloration and wing pattern, at least to the human eye, which, unlike that of butterflies, does not perceive ultraviolet (UV) light. However, these species can be reliably distinguished by karyotype and molecular markers. In this article it is demonstrated that cryptic species of the monomorphic complex are quite variable in wing pattern coloration in the UV spectrum. Unexpectedly, a very high level of intraspecific morphological variability was found, which concerns the degree of UV reflection and absorption by the wings or their parts, as well as the presence or absence of various elements of the wing pattern. This variability far exceeds those few variations of a single plan that is seen in the visible spectrum. At the same time, it is important to note that all these differences are intraspecific rather than interspecific; that is, the butterflies are morphologically polymorphic, but the species themselves do not differ. In this work 13 types of UV pattern are described, their distributions analysed across species and populations as well as differences in UV pattern between allopatric and sympatric populations. Variability in UV coloration in butterflies within the Agrodiaetus monomorphic complex and its probable relation to caterpillar food preferences are discussed.