Caterpillars belonging to a species of butterfly previously unknown as far north as Canada have been discovered in Montreal, in a sign that this country\'s cool climate is warming, researchers said Monday. The city\'s botanical garden and insectarium said the giant swallowtail butterflies (Papilio cresphontes Cramer) were recently found for the first time on a prickly ash plant there. \"The butterfly\'s arrival in Montreal is a very clear example of the impact of climate change,\" said a statement. \"In recent decades, milder temperatures in Nordic zones have enabled it to survive the winter and colonize new habitats. Giant swallowtails have gradually moved into Quebec, and the first native chrysalises are about to undergo metamorphosis at the botanical garden any day now!\" Giant swallowtails normally live in Central and South America. Starting in the late 1990s, they began showing up in North America as far north as the southern tip of Canada. While other butterfly species are also edging northward at a rate of 16 kilometers (10 miles) per decade, the giant swallowtail is moving into new habitats at a rate 15 times faster than average. Its range now extends a full 400 kilometers (248.5 miles) into areas previously too inhospitable to support a viable population. With a wingspan of up to 15 cm, or the size of a dinner plate, it is the largest butterfly in North America.