1. Many insect species are migratory. As the spring progresses, adults gradually depart from their over‐wintering habitats and arrive in northern zones where they reproduce during the summer. Understanding this transgenerational and highly adaptive migratory behaviour is crucial when interpreting life cycle dynamics of many insect pests.2. Origins of migratory silver Y moths, Autographa gamma (Linnaeus, 1758), captured from Finland, were studied with stable hydrogen analysis of their wings (δ2Hw).3. The difference between spring and autumn generation δ2Hw values indicate different geographical natal origins. The probability surface map shows that the spring generation probably emerged in central Europe (Benelux countries, Germany and parts of France).4. A negative correlation between the δ2Hw values and the migrants' capture year suggests that a warming climate may have driven the transgenerational migratory stages northwards during the last century.