Monarch Butterfly

Today we will learn about an insect that smells things with its antennae, tastes things with its feet, and has no ears but can hear ultrasound. If all that was not odd enough, they also have a compass in their antennae.


Monarch butterflies (Danaus plexippus) are fascinating uber-travelers. And they are struggling in our modern age.

Female monarch butterfly (Kenneth Dwain Harrelson) CC BY-SA 3.0

Monarch migrations
  

You might think it impossible, but delicate monarch butterflies travel 50 to 100 miles daily when migrating. Researchers recorded one overachiever clocking in with 265 miles in a single day! 



And it takes four generations to reach their destination. You read that correctly - four generations.



While some western variety monarchs have North American overwintering sites, eastern monarch butterflies migrate more than 3,000 miles to get from their winter homes in Mexico to their summer homes elsewhere. Monarch butterflies have also been raised on the International Space Station. I can only imagine what their internal navigational systems had to say about that.

Monarch identification


Often mistaken for viceroy butterflies, iconic monarchs have a 4-inch wingspan with orange panels and black and white markings. Viceroys have additional black lines across the rear wings. Monarch butterfly wings change shape and color at the start of migration, the same way salmon alter their bodies during migration. Like other butterflies, monarch butterflies pollinate your garden, flitting from flower to flower in search of nectar.

Viceroy butterfly (Benny Mazur) CC BY 2.0

Monarch populations


Traditionally, easter monarch butterfly populations have been measured by how many acres of land they cover when they overwinter in Mexico. In 1996-97, they covered more than 18 acres, which translates into approximately 1 billion butterflies. By 2014, that number dropped to only 1.6 acres. In simple terms, this indicates a 96% drop in population. Before jumping to conclusions, it is important that we understand there have not been comparable drops in summer populations, and scientists do not know why. 



Monarch butterfly feeding and breeding grounds


Monarch butterflies lay their eggs on certain types of milkweed because those are the only plants the larval/caterpillar stages can eat. Popular rhetoric blames herbicides for killing these particular types of milkweed, but many regular monarch habitats are flush with milkweed - and there have been no monarchs. There are mixed opinions on why this is and what it means.



As monarch numbers dropped, people became worried and started planting milkweed and nectar plants to provide global food and habitat corridors for the lovely monarch butterfly. In less than one year, news agencies announced that monarch populations had risen from 1.6 acres to 2.8 acres as a direct result of these actions. Sounds great, but it is not that simple. 



More monarch populations are appearing in previously unused areas. Some Monarchs are not migrating at all. Instead, they stay where they are and feed on popular tropical milkweeds that grow year-round. Sounds great, right? Well, it is, and it isn’t.



In “normal” eastern monarch cycles, winters are spent in a state called “reproductive diapause” which means the butterflies are not sexually active. Since native milkweed plants go dormant in the winter, everything was in balance. The tropical milkweed (Asclepias curassavica) does not go dormant in winter, so monarchs can stay in the same place year-round and forego the migration. The only problem with this is that continuous feeding has led to the emergence of a microbial parasite, called OE for short, that can weaken significant numbers of an already stressed species.

Monarch butterfly larva on milkweed (Kate Russell)

What is a gardener to do?


If you would like to help the monarch butterfly on its road to recovery, you can plant milkweed and nectar plants in your yard or on your balcony. Cosmos, marigolds, and zinnias are very easy-to-grow flowers that provide nectar, but you will still need to provide the proper type of milkweed to support monarch caterpillars. When shopping, look for native milkweed plants, not tropical varieties. If you already have tropical milkweed plants, you have two choices: rip them out and replace them, or trim them back 3 or 4 times a year, to interrupt the parasite’s lifecycle.

UPDATE (3/6/2016): Due to conservation efforts, the 2015-16 winter count of monarch butterflies reached 10 acres.

​UPDATE (11/20/2016): I added milkweed to my garden and now have half a dozen monarch butterfly caterpillars munching away on the leaves and what looks like a few more eggs getting ready to hatch - and all that is on a single plant!

UPDATE (1/3/2017): Frost has killed the aboveground portion of my milkweed and there is no sign of Monarch caterpillars or chrysalis.

UPDATE (4/13/2019): The milkweed is coming in strong!