This past Saturday was a stellar day at Severson Dells. It was the latest in our Science Saturday series, and we focused on monarch butterflies. The weather was perfect, and visitors came out in droves.
If you didn't make it, here's what you missed:
The Animal Farm Band performed in The Grove to a roving audience of parents and adults. Their music was engaging, and we even had families doing yoga and dancing to some of the tunes! After the show, they invited the kids to come up and play a couple of the instruments - what fun!
The Southern Wisconsin Butterfly Association had a table set up in our classroom and they were able to answer not only all sorts of questions about butterflies in general, but were also able to share dragonfly information with visitors, for one of them has authored a dragonfly ID book.
But the day really was a focus on monarchs, a species that is facing a variety of obstacles for survival. We had a handful of live caterpillars and chrysalises on display, which we collected and are raising inside so visitors can see the process up close and in person. Visitors were able to plant swamp milkweed seeds in newspaper pots that they made, to take home and plant, and we were also giving out local wildflower seeds, so visitors could create their own pollinator patches at home.
Why are monarchs in distress? There are so many factors contributing to their decline: habitat loss (wintering habitat in Mexico is falling to timber harvesting, and all along the route north, milkweed patches are disappearing - more on this in a moment); increase in disease; and, dare I say it, climate change.
Let's take a look at the one that we as individuals can all have a hand in controlling: milkweed. As every grade school child knows, monarchs are completely dependent on milkweed - it is the only food the caterpillars eat. That said, there are many different species of milkweed, each adapted to specific habitats. The most common one is, well, common milkweed (Asclepias syrica). This is the one that we used to find in every field and along every roadside. If you find yourself in wetter areas, you've probably encountered swamp milkweed (A. incarnata), with its brighter, more magenta blossoms. In our prairies and grasslands, butterflyweed (A. tuberosa) stands out with its brilliant orange flowers and its shorter, almost bushy, form.
These three are the milkweeds most people have seen, but our part of Illinois is home to a few others, like poke milkweed (A. exaltata), which is our only woodland milkweed and has flowers that remind me of an old-fashioned firework; sand milkweed (A. amplexicaulis); woolly milkweed (A. lanuginosa), a state threatened species (it's rare); purple milkweed (A. purpurascens); prairie milkweed (A. sullivantii); whorled milkweed (A. verticillata), which has such thin, thread-like leaves that at first glance you would dismiss as a milkweed until you looked at its beautiful cream-colored flowers; and short green milkweed (A. viridiflora). So many different colors, and all glorious.
The thing about monarchs and milkweed is that whichever species the female lays her eggs on, that is the species the caterpillars must eat, so there needs to be plenty of it around for the larvae to visit in order to get enough food to survive. Also, if you collect the eggs or caterpillars to raise indoors, you need to have a source of the milkweed species you found them on so you can continue to feed them while in captivity.
When I collected the caterpillars three weeks ago to have on hand for this program, I had no idea how difficult it was going to be to find enough common milkweed to keep them fed. I've been involved with raising monarchs indoors for a number of years, and milkweed has been incredibly easy to find - after all, it does grow along roadsides! But this year I had to scour the roads and fields near Severson Dells to find enough young plants to harvest to keep our larvae fat and happy. And I only had eight caterpillars!
Why is this? One of the reasons is directly related to the change in agriculture. With large-scale farms growing huge monocultures of corn or soybeans, we find less and less milkweed on the landscape. Once upon a time, milkweed grew alongside these crops - it wasn't too much of a competitor and the butterflies were able to find enough to carry on. Modern farming practices, however (and this is just in the last few years), have turned to crops that have been genetically modified to be "Round-Up Ready." This means that they are resistant to the herbicide Round-Up, so after the crops are planted, the farmers can go through and spray the fields with this herbicide to kill off all plants that are not their crop plants. This keeps the competition down and increases their yield. Unfortunately, this means there is no milkweed in the fields or on the field margins any more, which is problematic for monarchs, especially as they migrate north.
You see, monarchs have a bit of an unusual life cycle. Let's start off with the ones that are here right now. We are part of the northern range of these butterflies, and the ones that are emerging now are the last of this year's cycle. This generation is the one that flies all the way down to Mexico to for the winter. Those that survive the winter start to head northward the next spring. They stop in Texas, or some other southern location, where they mate, lay eggs and die. Those eggs hatch, and the caterpillars that successfully become butterflies fly the next leg of the Journey North. They, too, stop part way north, mate, lay eggs, and die. It takes four generations to make it to The North. The fifth generation is the final one, and that is the one that then heads back to Mexico in the fall. So, you see, if there isn't milkweed all along the routes these butterflies take as they fly northward, then there is no food for the caterpillars, and that means there won't be a next generation.
Disease and parasites also contribute to the decline in monarchs. One disease is called OE, which is short for Ophryocystis elektroscirrha, a protozoan parasite that the caterpillars ingest as they eat the milkweed plants. Not all milkweed is infected, but the infections are on the rise. The spores are spread by the adults, and as more and more monarchs are raised in captivity in butterfly houses and to sell to classrooms and brides, the more it spreads, for the spores are often contained in the captive “ecosystems,” and when the butterflies are released, they take the spores out into the wild with them. And thus the contamination spreads.
A “newer” disease is called Black Death, or NPV (nuclear polyhedrosis virus). If your caterpillars seem to suddenly “deflate” and then turn black, you have NPV. Well, YOU don’t, but your caterpillars do, which means your enclosure is infected (if you are rearing them indoors). This is a virus that is commonly found out in the wild, but in “normal” situations, it isn’t too much a problem. More on this in a moment.
Monarch caterpillars also have to contend with other parasites: chalcid wasps, which lay eggs in the chrysalises before they harden, and tachinid flies, which lay eggs on the caterpillars. The larvae of these parasites consume the host – they live and it dies. And then there are assorted fungi that can kill the caterpillars, as well as pesticides, such as Bt. Bt is Bacillus thurigiensis, a bacterium that is sprayed on crops to prevent pests from eating the plants. But the bacterium doesn’t just fall on crop plants when the fields are treated. If it lands on milkweed, then the monarch caterpillars ingest it, and, like the “pests,” they are infected by the bacterium and die within three days.
I mentioned climate change – how can this be affecting monarchs? Let me take you back to NPV for a moment. This virus, in the wild, is often kept in check by the chill of winter. However, with good old-fashioned cold winters on the wane these days, NPV is surviving in greater quantity than before.
Climate change is also affecting migration. Two things tend to trigger migration in animals: day length and temperature. While day length is unaffected by climate change, temperature is not, and studies have shown that the monarch’s fall migration has been delayed by as much as six weeks in recent years. If the butterflies do not leave when they should, then the chances of them finding enough food (flowers for nectaring) as they head to Mexico becomes slim. In other words, that fifth generation may starve before reaching the wintering grounds, which means there will be no (or fewer) monarchs to head back north come spring.
It's a complicated thing, life is. And the more we learn just how intertwined each component is on this planet, the more we see just how prescient John Muir was when he said "When we try to pick out anything by itself, we find it hitched to everything else in the Universe."
So, plant more milkweeds! Plant all kinds – find out which one(s) is/are right for where you live. (Don’t plant the tropical milkweed – it isn’t native and comes with its own host of problems.) And while you are at it, plant other native flowering plants – provide food for other insect pollinators who are facing a genuine food desert out there.
And come join us for our next Science Saturday (September 30), when we will be going crazy over more insects. It will be Insect Insanity, and who knows, you might even get to sample some edible insects…yum!