The New York Times reports that monarch butterflies migrating from North America to central Mexico appear to be doing better than last year, when the over-wintering colony occupied just 1.7 acres. This year’s survey finds the butterflies have filled 2.8 acres, which seems like a solid improvement until you consider that the peak colony size, since record-keeping started, was 44.5 acres.
(Incidentally, 44.5 acres is more than 40 American football fields of forest covered with roosting monarch butterflies.)
The monarchs that migrate to Mexico aren’t the only population — there’s another migratory route on the U.S. Pacific coast, and there are non-migratory populations in Florida, Hawaii, and even New Zealand. But the Mexico overwintering site represents what used to be the single largest monarch population, butterflies that spend summer across most of North America east of the Rocky Mountains. Logging in Mexico and the loss of summer habitat to farming in the Midwest has been hitting the butterflies hard for years, and while this rebound is encouraging, it might still make sense to put the monarch on the Endangered Species List, as the U.S. Fish and Wildlife Service is considering.
Monarch butterflies (Danaus plexippus) are among the most widely recognized wild creatures in North America. Their distinctive orange-and-black wings, which warn predators that the butterflies are chock full of toxins from the milkweed they eat, make them easily spotted in backyard flower beds. They’re also known for a massive annual migration, flying thousands of miles between wintering colonies in central Mexico and summer sites across the United States and Canada. More recently, it’s been discovered that female monarchs infected by parasites respond by laying their eggs on food plants that can prevent the parasite from infecting their offspring.
Monarchs are also one of the more visible victims of the massive changes humans have made to the world around us. Increased conversion of farmland to corn production has reduced the supply of milkweed, the butterflies’ only food plant, across much of the Midwest. It’s gotten so bad the number of monarchs making the annual migration back to Mexico hit a record low last year, and while things were better in 2014, a nationwide campaign to encourage planting of milkweed in home gardens is only beginning.
For all our familiarity with monarchs, we’ve known remarkably little about their evolutionary history. That’s changing rapidly now, as evidenced by a paper published last month in the journal Nature, which uses a big new genetic dataset to trace the origins of some of the monarch’s most distinctive features.