This butterfly is famous for its vast migrations across the North American continent and its communal roosts in Mexico. It also crosses the Atlantic Ocean in small numbers and regularly turns up on the south western coasts of the UK. Like the Clouded Yellow, there are irregular good migration years and it can be found around the Cumbrian coast.
Where to look
Anywhere on the coast, historically the best area is the Furness peninsula.
When to look
Mid-September to mid-October in a good migration year.