Agelastica alni, the alder leaf beetle, is a species of leaf beetle (Chrysomelidae) in the genus Agelastica. Agelastica alni is distributed in Europe, the Caucasus, Siberia, north-eastern Kazakhstan, and in the 19th century was introduced to the United States. Previously rare, and considered extinct in the UK, since being found in Manchester in 2004 it appears to be on the increase in the North West of England. Its range has been extending and it was found in Nottinghamshire and Hampshire in 2014 and in North Wales in 2018.