Probably the most iconic butterfly, the monarch (Danaus plexippus), in all its orange glory, has blazed its way onto the International Space Station (no kidding). Together with the painted lady (Vanessa cardui), it’s being studied to determine how and whether it can complete its life cycle in space. I don’t know what the astronauts were thinking, but one hopes this has less to do with caterpillar-flavoured space food, and more with the birds and the bees (for lucky space plants).
First described by Carl Linnaeus in 1758, North American monarch butterflies have since become famous for their annual mass migration from northern and southern U.S.A. and southern Canada to California, Florida and Mexico- a very smart move that we humans could certainly learn from, except that we’d probably cause traffic jams instead. Besides the cold, the lack of the food source for their larvae- milkweed plants- in the winter also drives them to migrate. They seek shelter in various roosts, including golf courses and lighthouses along the way, before settling in oyamel firs, elms, willows, mulberries, cottonwoods and a number of other types of trees at their destination. Although caterpillars only eat milkweed plants, adults feed on nectar from a number of different flowers, including that of asters, thistles, red clover, goldenrod, and many others. Here, in their overwintering sites, they procreate for four more generations, and offspring make the return trip in March. There are two possibilities to this: one being that they have inbuilt GPS systems that would make the best tech companies jealous; two that there exists a means of passing down information between generations, or communicating between butterflies, a butterfly whisper that we haven’t come to learn. The latter’s perhaps the more romantic explanation, although the former’s more likely to be true.
Monarchs take cues from the environment in deciding when to leave. In the autumn, usually September or October, they depend on the angle of sunlight, temperature, day length, and host plant abundance. Males and females are built differently, even in insects. Males are generally larger and heavier, but females have thicker wings to help make sure they don’t get damaged as easily. Due to a larger wing size to body weight ratio, female butterflies have an easier time flying than the males.
Although Mexico has enterprisingly designated monarch butterfly overwintering sites in Michoacan as a Monarch Butterfly Biosphere Reserve, its preppy website masks the sad truth: the migrating monarch butterfly population is in decline. According to reports, more than 700 million butterflies made the annual migration in the 1990s. By 2004, this number had dwindled to 550 million, and in 2013 only 33 million made the trip. Various studies have identified contributing factors to the monarch’s decline, including storms (which managed to blow down 100 acres of forest in 2016), climate change, decreased milkweed populations as a result of herbicide usage, and deforestation. Although some believe that decreased milkweed populations is the key factor, researchers in Cornell university discovered that populations actually declined only during the migration itself, building up again after their return trip North. They attribute this to a decline in clean and unpolluted landscapes along the route, providing fewer roosts, fewer flowers to feed on along the way, and a lack of habitats at their destination due to deforestation. As aptly put by Dr. Agrawal, the lead researcher, “this is a complex problem to which there are no simple solutions”.
But of course, given that there’s enough that’s messed up in the world already, I’ll end this on a more optimistic note: there’s a silver lining. People have been tagging and studying monarchs for years. One good thing about voices being raised for the butterflies is that efforts will hopefully be made to aid them.
- Stenoien C, Nail KR, Zalucki JM, Parry H, Oberhauser KS, Zalucki MP. Monarchs in decline: a collateral landscape‐level effect of modern agriculture. Insect Science. 2016 Nov 1