Usually we think of islands as delicate ecosystems, sensitive to change because of the few numbers of species there and their complex interactions that can be upset by the loss (extinction) or addition (invasion) of a species. However, through the introduction of a couple of milkweed plant species, Maui, as well as Oahu and the big island of Hawaii, seem to have become a refuge for Monarch butterflies, whose populations are crashing in various parts of mainland North America.
In the town of Kapalua on the northwest shoreline of Maui, a very hilly and abandoned golf course has become a refuge for all sorts of exotic plants and animals like the Monarch butterfly.
Dozens of Monarchs flitted about us as we walked. I don’t think I have seen this many Monarchs in an entire summer (or two) in Minnesota, but here they are thriving with plenty of the balloon milkweed leaves for the caterpillars to feed on and the nectar of this and other flowering plants in the overgrown golf course to sustain the adults.
It’s possible that Monarchs have become established on the Hawaiian islands by founding individuals from California, but that is a 2400 mile journey, and the wind generally blows from west to east, not the reverse. Unlike the California population, island Monarch butterflies are not migratory, so once they have found isolated patches of milkweed, populations thrive and increase. In addition, several butterfly “farmers” in Hawaii market their Monarchs for weddings, with additional individuals being released to the island as the couple pronounce their vows.
So here’s a rare story of how an introduced plant species benefits the survival of a species that is threatened in other parts of its range. It’s a wonder how the butterflies find their milkweed hosts (needle in a haystack?), but impressive when they do.