Oedaleus decorus is a widely distributed species over the Eurasian semi-arid territories, from the Atlantic coast to the Pacific one. In many semi-arid territories, O. decorus was and is the important pest. In the south-eastern part of West Siberian Plain, until the 1960s it was not considered a pest. We compared two sets of data on the acridid distribution in the region: until the 1950s and from the 1960s until 2019. Until the 1960s the species occurred mainly in the southern steppes. Since the 1960s its distribution changed significantly. Nowadays it occupies almost all local steppes and the southern part of the forest-steppes and was also found on the eastern side of the Ob River. These shifts may be explained by both climatic changes and changes in human activities. During upsurges the densities of O. decorus were often more than 1–2 adults per square meter. It was and is often abundant in the same habitats and in the same periods as the Italian locust (Calliptamus italicus) – one of the most important pest. This means during joint outbreaks these two species can simultaneously damage almost all spectrum of plants.