Monarch butterflies migrate north from Mexico in early spring and go through three or four reproductive generations on their way to the northern US states and Canada. In the spring, the migratory individuals transform to a reproductive phase and mate before departure. As the migratory females fly north they deposit eggs only on milkweed in southern Texas and die within two weeks. The eggs hatch in four days and the larvae grow over two weeks eating milkweed leaves before spinning a chrysalis and entering the pupa stage. The adult emerges after another two weeks and lives on the nectar of several flowering wildflowers as it moves further north to continue the progression of successive generations. Spring and summer adults live only a few months but the last and migrating generation enters a non-reproductive diaphase stage that lives up to eight months enabling it to migrate back to Mexico, over winter and begin the return journey north.
A number of factors contribute to the reduction of the Monarch populations. The loss of milkweed from the agricultural areas of the mid-west United States, southern Ontario, Quebec and the Maritimes have had the most drastic impact on Monarchs. The use of herbicides on and mowing of roadside corridors and shoulders also reduces milkweed. Illegal logging and tourist invasion in the Michoacan sanctuary have reduced the wintering habitat. Changing climate patterns of more extreme temperatures and rainfall are affecting survival of migrating and over wintering butterflies and impairthe reproduction of successive generations traveling north.
MOSAiC Article – Mosaic – Monarchs – Fall 2014
Some interesting links:
Life Cycle of Monarchs
Migration of Monarchs
Donald Barber – Tagging Monarchs
Dr. Chip Taylor – Challenges Ahead