This article examines the history and usage of a specific type of phraseological units with the components “raven” and “crow” in Bulgarian and Polish. These phraseological units have a common origin related to the ancient cultural heritage of European nations and initially shared a close meaning. However, their development in the two languages takes different paths, leading to the emergence of interlinguistic asymmetry. The conducted research demonstrates that interlinguistic equivalence relationships in phraseology are dynamic and can change over time depending on the characteristics of intra-linguistic developmental processes.