The Monarch Migration
As I write this, we are in the midst of the southern migration, which generally starts around the middle of August, according to the U.S. Fish and Wildlife Service. It’s time for the butterflies to begin the overwintering process and proceed to their winter homes. Why? Because they cannot live through the colder temperatures. Cold to a butterfly is not the same as a human. Butterflies are “ectotherms,” that is, they cannot generate their own body heat. Once the temperature drops to around 57 or so, they are too cold to fly and will die.
In the U.S., there are two distinct monarch populations. The western population are those that eclose (leave their chrysalis and become butterflies) west of the Rockies and the eastern population which are those that eclose east of the Rockies. The western population overwinters in California where they hibernate in the eucalyptus trees. The eastern population will got to Mexico to the oyamel forests. This journey can be as much as 3000 miles! They are guided by the sun for about 50 miles per day, watching for feeding and nesting sites as they go. Between the two populations, nearly every part of the U.S. is visited by monarchs. This is why I think of it as America’s butterfly. It is also the most recognizable of all the butterflies.
If you’ve heard that most butterflies live for only about 4 weeks, and this is true for most monarchs. The early season monarchs live only for a short time and basically do nothing but eat and procreate. But those that eclose after the end of August are special. This is the “Super Generation,” the fourth or fifth generation of the season. These monarchs live up to 9 months, long enough to make the tough migration, overwinter and begin the flight north. Unlike previous generations, the super generation is not fertile until after overwintering. This is to help them preserve fat and energy for the many miles they must travel.
I cannot emphasize enough what a treacherous journey this is, both going north and going south. Why? Lack of food is a problem, especially if they leave their wintering grounds too early. This year, the migration started too soon because of the unusually warm weather. The monarchs started their migration, but the milkweed hadn’t grown in, so starvation was prevalent. There are always predators along the way. While you may have heard that they are protected by their vibrant colors, which indicate that they are poisonous, that doesn’t stop birds, lizards, etc. from eating them. They may only try it once, but once still counts.
According to Andy Davis, research scientist at the Odom School of Ecology, University of Georgia, monarchs are often not able to make the distance over huge lakes and may drown. They get caught in storms. The southern migration takes place in the heart of hurricane season. The biggest single cause of death during migration is roadways! He estimates that around 25 million monarchs per year are hit by cars.
There’s not a lot we can do about traffic, but we can help in other ways. Planting milkweed and nectar flowers to provide food is one of the best things we can dod to help them along the way, both north and south. But in order to make this work, we must shun pesticides and herbicides. Even pesticides labeled as “organic,” such as BT (Bacillus Thuringiencis) is lethal to monarch larva, along with ubiquitous RoundUp which is against the law in many other countries but still in common use here in the U.S. So, when you’re planting or taking care of your lawn, please thing of our butterflies! This of course applies to all pollinators, such as bees, birds, moths, etc. Remember that every third bite of food you eat has needed a pollinator to get it to market. IF YOU WANT TO EAT, YOU MUST SAVE OUR POLLINATORS!
