Written by: Mason Hoffman (August 2023)
We often hear about or directly deal with harmful insects that eat our garden plants and our crops. I myself have been battling spider mites on my houseplants for almost two years now. If I don’t diligently scrape them off every few days, my basil plant will get sucked dry. However, the relationships between plants and the insects that eat or parasitize them are not always so damaging. In fact, they often lead to increased biodiversity and greater numbers of organisms within a given ecosystem. Let’s first look at a well known example, monarchs and milkweed.
All milkweed species native to Illinois serve as host plants for monarch eggs and caterpillars. Monarchs and milkweed co-evolved together. Monarch caterpillars are able to eat the somewhat toxic vegetation of milkweed, and they even turn it to their benefit by accumulating the cardenolides (heart toxins) the plant produces in order to become poisonous to most mammals and birds. In turn, milkweed plants defend themselves from caterpillar grazing by producing more latex, developing dense trichomes on the undersides of their leaves, and growing back vigorously after grazing. The relationship between monarchs and milkweed is complex and constantly evolving. Milkweed plants certainly don’t appreciate being eaten, but since the plants have been dealing with hungry caterpillars for millennia, they have enough adaptations that the monarchs never solely kill a milkweed plant. This is good for the caterpillars as well, because if the 2nd generation kills all the milkweed in an area, there will be none for the following generations to eat.
The arms race between the two is still going on, but it’s in a somewhat stable state. Because of the parasitism of monarchs, milkweed plants confer more value to an ecosystem than they could entirely on their own. The caterpillars provide food for plenty of other insects and the few animals that can eat them, and the adult butterflies pollinate a plethora of prairie plants, including milkweed. So milkweed is a great native host plant for people to include in their gardens and landscaping, but there are so many more host plants that support beloved and important insects!
Monarch caterpillar on butterfly milkweed
Chief among midwestern native host plants are the oaks! The white oak takes the cake as the most generous of midwestern plants, hosting over 200 species of insects. There are scale insects who eat the leaves and bark and whose honeydew (poop) attracts and feeds ants, bees, and wasps. There are gall forming insects who cause leaves to form around their eggs, providing food and shelter to the vulnerable larvae. There are dozens of moth and butterfly caterpillar species that white oaks host, which in turn provide food for birds. Caterpillars make up the majority of the diets of many nesting birds, providing food at a critical time in their life cycles.
White oaks are also just amazingly cool in their own right. They regularly live for hundreds of years and can even reach 500 years of age. They can soar to almost 200 feet tall in a competitive forest, but they really shine as part of a nearly lost midwestern ecosystem, the oak savanna. Their fire resistance and ability to resprout allowed them to grow in frequently burned areas where most other trees cannot, creating an oak savanna. Oak savannas are extremely biodiverse ecosystems, capable of supporting a wide variety of birds, mammals, and insects. This is due to the gradient that they create, where habitat exists for full-sun prairie plants as well as shade-preferring plants in the shadow of mighty bur and white oaks.
Restored Oak Savanna
Enough about host plants you likely already know about, or trees that take years to mature. I wanted to write this blog to share (and discover for myself) some lesser known native plants that host amazing organisms. Wild blue lupine, or Lupinus perennis, is the sole host of the Karner blue butterfly. The Karner blue is a small, spectacularly colored, and critically endangered butterfly found around much of the Midwest. Planting some wild lupine is one way we can work to save this beautiful butterfly. Wild blue lupine is also host to quite a few other butterflies, whose awesome common names include the frosted elfin, the wild indigo duskywing, and the clouded sulfur.
A Karner Blue butterfly gathering nectar from wild lupine flowers
There are many examples of prairie plants that support a surprising amount of biodiversity. The leadplant is a shrubby prairie plant that is known for being extremely drought tolerant and long-lived. It supports 35 species of caterpillars and its long-lasting blooms are magnets for native bees. The four species of goldenrod native to Illinois support over 100 species of insects! It also makes a great addition to any garden by providing some late-season color. Black oak, river birch, eastern cottonwood, and box elder are just a few examples of trees that are utilized by over 100 insect species each!
This blog could go on and on listing more species of native plants that support insects of all shapes and sizes. There are a few links below that you can click through to find expanded lists, growing regions, and ideal conditions for native plants and trees. If you like seeing birds, bees, butterflies, bats, hawks, frogs, deer, or any of the amazing wildlife we have here in the Midwest, planting natives is the best way to get to see more of them (plus removing invasive species when you can). It’s also a good step towards assuring that future generations will even be able to see them at all. Terrestrial insect populations are declining at a rate of about 1% every year. And they’ve been doing so for decades. And it’s not just insects. Global vertebrate populations have fallen by 69% since 1970! If you’ve ever wondered why you see less frogs and snakes and butterflies than when you were a kid, it’s because there are less. The extinction we’re facing can be terrifying, and it can feel hopeless. But we live during a critical period where complete disaster can be avoided. Pushing for sweeping climate policy reform, better city planning and more robust environmental protections is absolutely necessary if we want to avert total ecological collapse. But nothing can help quench that feeling of existential climate dread like seeing a baby caterpillar munching away in the garden you cultivated, or watching a pollen-laden bee traipse from flower to flower that you sowed, or watching birds raise their young in tree you decided to plant.
Helpful Links:
Wild Ones: http://wildonesrrvc.org/Native_Plant_Resources.html – A local native plant org. with excellent info as well as lists of native plant sellers and further resources.
DNR: https://dnr.illinois.gov/education/plantlists.html – The Illinois DNR provides lists of plants for various goals and habitats that would be an excellent starting point for any aspiring native gardener.
