We know monarch numbers have declined drastically in recent years. Estimates are down by 80 to 90% from a population size of about one billion in the early 1990s.
It’s long been thought that the big reason behind this is the loss of milkweed throughout the farming regions of the U.S. Midwest. With the introduction of GMO crops in the mid-90s, and pesticides and industrial farming practices, the milkweed has disappeared. No milkweed, no home for eggs or food source for caterpillars.
But according to Dr. Tyler Flockhart a post-doctoral fellow at University of Guelph, the number of monarchs coming from that region has stayed steady at around 38% for almost 40 years.
By looking at a collection of more than 1,000 preserved butterflies, he was able to determine that over 60% of monarchs have come from outside the U.S. Midwest.
So to what can we attribute the steep decline of monarch numbers? Flockhart says that milkweed has been lost from across the monarchs’ range, but that temperature and climate are contributing factors as much as farming practices.
He believes that knowing more about where they originate can help in conservation efforts, i.e. more focused planting of milkweed.