The Monarch is one of the largest butterflies in Canada and possibly the most well-known. It is entirely migratory, which means that it does not spend the winter here in any stage of its life cycle, but instead flies from areas much further south. Most of the butterflies arrive in June, then pass through two or three generations before the bulk of the population leaves in September. Numbers vary greatly from year to year due to weather conditions, which affect not only reproduction and migration, but also their survival rate over the winter.