Great news! Reports from the Monarch Butterfly wintering grounds in Mexico say that this will be another good year for Monarch Butterflies (Danaus plexippus) in our area! Monarchs of the Midwest and Northeast count on us to provide a big pulse of wildflowers with nectar to sip and lots of Milkweeds (genus Asclepias) on which to lay their eggs. Monarchs are very choosy! Their caterpillars can only become butterflies by eating the leaves of plants in the Milkweed family.
In February, Dr. Ben VanderWeide, our township stewardship manager, hosted an interesting and thorough presentation by Dr. Nate Haan of Michigan State University on the topic “Monarch Butterfly Ecology and Conservation.” So here’s a bit of what he shared with us that might help you and I be prepared for the arrival of these beautiful pollinators. My thanks to Dr. Haan for his presentation and to the photographers cited in the captions of some photos below for helping me tell the amazing story of our “super generation” of Monarchs.
The Life of a Monarch from Egg to Adult
One end of the Monarch migration starts each late summer/ autumn here in Michigan and other Midwest and Northeastern states. Monarchs that traveled here in spring sip wildflower nectar, mate and lay eggs on the underside of milkweed leaves. Their favorite milkweed is Common Milkweed (Asclepias syriaca), though any milkweed in the Asclepias species will do. More about that later.
Only about 2-10% of the Monarch eggs hatch in the fields, because they are food for a wide variety insects and spiders. But for the lucky few, small caterpillars emerge from these eggs. They begin by eating the egg itself and then going on to eat the leaves of the host milkweed plant. Milkweed has tiny silver hairs as a protection against predators, but over the eons Monarch caterpillars have learned to shave them off! They then attach their hind end to the leaf and move in a half circle eating, which prevents most of them from getting stuck in the milky latex that gives milkweed its name. Then the little caterpillar molts, shedding its exoskeleton to become an increasingly more colorful and larger caterpillar. It takes them five molts to reach full size.
The sticky, milky latex is the plant’s second defense against predators, because it can gum up a caterpillar’s mouth. But the fifth and last molt of the Monarch caterpillar has found an even more effective way to defuse the threat than the first instar did. The large yellow and black fifth instar’s technique is to make a quick bite into the main vein of the leaf, releasing pressure and waiting until the liquid drains out. Then they can continue to eat anywhere on the leaf. Here’s my photo of a fifth instar eating Butterfly Milkweed (Asclepias tuberosa) along the Paint Creek Trail.
It takes 10-14 days for the caterpillar to complete 5 molts. It then leaves the milkweed behind, finds a horizontal surface, attaches itself with a silk pad and molts again. This time the caterpillar creates an opaque green chrysalis with gold trim! The chrysalis hardens after a short time and the butterfly begins to develop inside. This pupal stage lasts for another 10-14 days.
Finally, the chrysalis becomes transparent and the the butterfly emerges to dry its wings before taking flight.
The Super Powers of our Monarch “Super Generation”
The Monarchs fluttering over our parks in August and September are gifted with two super powers: they live much longer than other Monarchs, and they can fly over 3000 miles to overwinter in Mexico. I’ve cited this quote from National Geographic before in discussing monarchs but it bears repeating. According to Dr. Pablo Jaramillo-López, a research scientist at the National Autonomous University of Mexico “…when fall rolls around …, a special ‘super generation’ of monarchs that can live up to eight months will make use of air currents to wing all the way back to Mexico—a seemingly impossible feat for such a delicate-looking insect.”
It can take up to two months for our Monarchs to reach the mountains of central Mexico. They spend the winter there, protected by the micro-climate created by Oyamel, or “Sacred” Fir trees (Abies religiosa).
In the spring, our “super generation” monarchs then start the journey back to Michigan by flying as far north as Texas. After mating and laying eggs there, they die, and their offspring carry on the migration north. It takes four or five generations of Monarchs along the way, each living only 5-7 weeks (instead of 8 months!) for the last of our super-generation’s offspring to land with such exquisite delicacy on the wildflowers in our parks. As Dr. Pablo Jaramillo-López says in National Geographic, “This makes the migrating monarchs so unique as they are the same species but for some reason live much longer.”
The Threats that Monarchs Face
Monarch numbers go up and down but sadly, over the last two decades the trend is generally downward as you can see above. So what’s the problem? As usual, there are multiple factors. Dr. Haan named five:
- Logging in their overwintering area in Mexico makes surviving in the mountains more difficult. The Mexican government and non-governmental organizations are working on finding sustainable projects that can support local economic alternatives for people living in the Monarch’s wintering grounds.
- Less wildflowers and more agricultural crops in the Great Plains and Midwest states. This leaves less nectar resources to feed the Monarchs and fewer milkweed stems on which to lay eggs for successive generations. Some farmers are changing their approach to their grazing and crop land to accommodate the Monarch’s need for milkweed.
- According to the Monarch Joint Venture website, OE (Ophryocystis elektroscirrha), a parasite can get on the wings of adult Monarchs, who then spread this parasite on the milkweed leaves when they mate or lay eggs. If caterpillars eat the leaves, they become infected with the pathogen that can cause a developing Monarch’s wings to be too weak to get out of its chrysalis and may shorten the lives of adult Monarchs. Tropical forms of milkweed sold by nurseries tend to be associated with this parasite and they should be avoided. Dr. Haan reported also that Monarchs bred from more tropical areas, like Florida, may carry OE, too.
- Insecticides used on garden plants can be lethal to butterflies, as well as other beneficial insects. Perhaps the greatest problem is milkweed loss in the Midwest, which is the core breeding habitat for Monarchs. Milkweed used to be much more common around and on farms.
- In the late 1990’s many farmers turned to Roundup Ready genetically modified seeds which makes their crops resistant to Roundup. This allows farmers to spray Roundup on their crops, which kills milkweed along with other unwanted plants without hurting their crops. As a result, Dr. Haan said, scientists estimate that 40% of the milkweed needed by Monarchs, is gone, maybe a billion stems in the last 20 years, which coincides with the decline in Monarch populations.
So How Do We Help Our Friendly Local Monarchs?
Well, we can use less insecticide and when we do use it, follow directions carefully. We can avoid growing non-native milkweeds that carry the parasite OE. We can plant milkweed to support developing caterpillars and nectar-producing native flowers to feed the adult Monarchs. Coneflowers, asters and goldenrods, and many other prairie flowers that prefer medium to dry soil and full sunlight flourish just when the super generation of Monarchs is beefing up for the long migration. Of course, lots of other butterflies, bees and other pollinators loves these flowers too!
Varied Milkweed Species Feed Young Monarchs and Add Color to Our Fields and Gardens
Maybe the biggest – and most beautiful – contribution we can make to the welfare of Monarch butterflies is to plant more milkweeds in our fields and gardens. Common Milkweed (Asclepias syriaca) multiplies both by the parachuting seeds we all loved as children and by its extensive network of roots. So it can spread too quickly to be a great garden plant. But it’s perfect in big sunny fields or natural areas.
If you are lucky enough to have Common Milkweed on your property, it will help, Dr. Haan told us, if you trim/mow down about a third of the milkweed stems on your property in late June or early July. He and his associate’s research shows that Monarchs prefer to lay more eggs on the tender stems that re-grow because they are easier to eat and more nutritious .
Since most of our milkweed plants are full grown by August, their leaves are old and tough and Monarch egg predators are present in large numbers. If you can trim or mow some of your milkweed plants in mid-summer, they will re-sprout and provide the softer leaves on which Monarchs like to plant their eggs in late July or early August for the migrating “Super Generation.” Those new stems also contain less predatory insects and spiders, meaning monarch eggs may have a better chance of surviving.
Luckily, If you’d like Monarchs in your yard or garden rather than a field, there are other kinds of milkweed for those settings. Butterfly Milkweed (Asclepias tuberosa) tends to stay in one place. It needs a dry to medium moisture level and lots of sun. And what a beautiful orange to match the Monarchs! Other butterflies and pollinators love them too, of course!
Swamp Milkweed aka Rose, Pink or Red Milkweed (Asclepias incarnata) also loves sun, but as the word “Swamp” implies, it likes “wet feet” or at least medium to moist soil.
If you have a shady area with medium to dry moisture levels, try planting the graceful Poke Milkweed (Asclepias exultata) with its cascade of bluish-white blossoms.
Native plant nurseries (see the list in an earlier blog) can show you other native milkweeds as well. If possible, find ones that are Michigan genotypes since they will grow most easily and serve admirably as host plants for our Michigan Monarchs.
So Rewarding to Make a Difference, Isn’t It?
Who knew, when I was a child, that milkweed plants would begin to diminish and the Monarchs would begin to decline as a result? And now we know, according to the recent summary of a biodiversity report, that as many as a million other species worldwide are in the same situation.
It’s easy to despair, I know – but let’s not! The best antidote to despair is always doing what you can in your own corner of the world and supporting others who share your concern for nature.
And in the case of the Monarch butterfly, it can be as simple as planting milkweed! Or it’s as easy as planting native flowers, grasses, shrubs, and trees in our yards instead of exotic plants. With no recent shared history, these exotic plants don’t always feed butterfly caterpillars and other beneficial native insects. Or, if you’re feeling adventurous, it’s changing the non-native turf of your own lawn into large gardens filled with colorful native plants with paths of mowed turf leading from one to the next. Or it’s maybe creating a native prairie out of an old agricultural field like our township stewardship crew and some nature-loving homeowners are doing.
All it takes is just caring, learning and getting started. I’ve begun. The township parks stewardship crew has begun. Many of you have already begun. What we can hope is that others will join us.