Mass Migration of Monarch Butterflies

mass migration of monarch butterflies
massed monarch butterflies

Scientific Name: Danaus plexippus (Linnaeus).

Monarch butterflies (also known in Australia as Wanderer butterflies) are well known for their migratory journey across the North and South American continents. Millions of Monarch butterflies migrate south in the autumn (September/October) in order to avoid the cold temperatures of the north during winter. The butterflies need to escape winter for two main reasons: they are incapable of flight/movement at low temperatures and the supply of nectar, their main food source, is heavily reduced.

The Monarch butterflies cluster together at their overwintering sites, usually in the same trees as the previous season. Each butterfly hangs with its wings overlapping those of the butterfly beneath it, forming a blanket over the trees. Their close proximity to each other enables the butterflies to retain warmth and the weight of the cluster also prevents the butterflies from being blown away during their hibernation.

In February/March, when the winter months have passed, the butterflies will awaken from their hibernation to mate and make the return journey to their original locations in the north. The butterflies must return north because the larvae feed solely on milkweed plants, which are not found at the overwintering sites.

When the butterflies reach their northern destination, they lay their eggs and then die. The life span of a Monarch butterfly is approximately 6-8 weeks (excluding hibernation times), therefore the next three generations of butterflies remain in the north and it is the fourth generation (which reaches adulthood in autumn) that will migrate south for the winter.

Photos courtesy of Harry O. Yates III, USDA Forest Service. Image 4911056 and 4911050,