Thousands of striking orange and black Monarch Butterflies began arriving to their winter home in Central Mexico in their annual migration.

The 3,000-mile mass migration of monarch butterflies in North America is one of the insect world’s fantastic feats, with millions embarking on the arduous journey from as far North as Canada down into Mexico and the California coast each autumn.

The number of migrating monarchs has been under strain in recent years. Experts said while an estimated one billion monarch butterflies migrated to Mexico in 1996, that number stood at about 35 million last year. Threats to them include habitat loss due to human activities, pesticides and climate change, experts say.