25 September 2013
A week ago I saw my first and only monarch butterfly of 2013. Their sudden disappearance is both troubling and saddening. It’s now possible to imagine a world without monarch butterflies. We are nearly there.
Last winter’s monarch survey in Mexico showed their population was down 59%, a record low. There have always been population fluctuations but the trend has been running low and lower since 2004. Scientists believe that agricultural pesticides and herbicides have reduced available poison-free habitat for butterflies (similar to the bees’ problem), so this spring monarch enthusiasts encouraged people to grow safe-haven milkweed for the butterflies. It wasn’t enough.
Each species has an intrinsic value. If, or when, the eastern monarch butterfly goes extinct we will lose its pollination contribution, milkweed symbiosis, beauty, and the amazing adaptations that allow multiple generations to migrate from Mexico to Canada and back.
One of the adaptations that will disappear is this: Monarch butterflies have a sun compass in their antennae.
Their antennae have light sensors that track the amount of light each day. According to a study in 2009 by Merlin, Gegear and Reppert, this circadian clock “provides the internal timing device that allows the butterflies to correct their flight orientation, relative to skylight parameters, and maintain a southerly flight bearing, as the sun moves across the sky during the day.” Migratory monarchs without antennae fly in aimless directions. Monarchs with antennae always orient southwest.
The monarch’s sun compass was discovered only a few years ago. Now there are almost no monarch butterflies to study. The world will be a poorer place without them.
Click here for more information on the monarch’s amazing sun compass.
(photo credits: monarch by Marcy Cunkelman, 2008)