Another Example of the Value of Thistles

Two painted lady butterflies compete with a digger bee for the bounty found in a native tall thistle (Cirsium altissimum) flower.

Thistles are among the most disliked plants in the world. Sure, they’re spiny, and some species have become invasive after being transported outside their native range. But thistle flowers are gorgeous, provide incredible resources for pollinators, and their seeds are nutritious wildlife food. American goldfinches even nest a little later than many other songbirds just (apparently) so they can feed thistle seeds to their kids.

So why do people hate thistles so much? Don’t tell me it’s because they’re spiny. The thorns of roses don’t seem to have hurt their popularity. In my neck of the prairie, a lot of people dislike our native thistles because they assume all thistles are invasive, or at least weeds. But even when they learn that species like Flodman’s or wavy-leaf thistles (Cirsium flodmanii and C. undulatum) are native, most people aren’t impressed.

A few years ago, I tried to get some momentum behind the idea that thistles are important for pollinators. That movement didn’t get far, despite it’s catchy (I thought) slogan. I still try to convince people they should be more open minded about thistles, but I don’t really have much hope of success. Despite that, I’m going to present one more piece of evidence on the side of thistle value. Stick with me – the story doesn’t start with thistles but I promise it’ll get there.

This past weekend, I spent two afternoons cutting eastern red cedar trees out of our prairie. For the most part, we catch and cut those trees while they’re still small enough to nip off with loppers. This weekend, though, I was working on the ones that had flown under the radar long enough to grow bigger than loppers can handle. As a result, I was using my noisy chainsaw to knock them down.

As I worked, I started noticing big clumps of grass and other material – mouse nests – embedded in the branches of a few trees. Some were at the bases of the small trees and others were a few feet up the trunk. All were empty, and it took me longer than it should to realize that they were probably vacant only because my noisy saw was scaring the inhabitants off before I got close. I felt bad about disturbing the nests but also really needed those trees to die before they started producing seeds and swarming over the whole prairie. I tried to keep the nests intact as I laid the trees down, hoping the little critters would move back in once I left.

As I neared one particular draw, I started finding a higher percentage of trees with nests in them, and the composition changed from mostly grass to mostly white fluff. Looking more closely, it was clear the fluff was from thistle seeds. I’m pretty sure most of the seeds came from a patch of bull thistles (Cirsium vulgare) I’ve been keeping track of. (Bull thistle doesn’t tend to be very invasive in our area, despite being non-native, so I’m pretty tolerant and just monitor them to make sure they aren’t going crazy.)

I don’t know if the higher abundance of nests in that area was due to the availability of thistle seeds – or even if they really were more abundant versus just being more visible because of their pale color. Regardless, they looked extremely cozy; the insulating value of thistle fluff has to be pretty incredible. Some of the nests were nearly the size of volleyballs and pretty hard to miss, even when obscured by branches full of dark green needles.

So, add one more attribute in the positive column for thistles – they provide great insulating material for winter shelters of mice. And don’t tell me you’re anti mouse and try to spoil my argument. Even if you don’t think mice are cute little critters, which they objectively are, the prairie ecosystem would fall apart without them. Among other things, they’re key food sources for many larger animals and important consumers/transporters of seeds.

Speaking of transporting seeds, the biggest mental image that sticks with me from seeing all those thistle seed nests is not the volleyball-sized masses of fluff. Instead, I’ve been obsessively thinking about those poor mice hauling all that fluff several feet up into those trees. First of all, that’s a tremendous amount of work – gathering the seeds from the tops of spiny plants, hauling it down the plants, across the prairie, and up into the trees. Over and over.

But they’re not carrying those seeds in their paws… they’ve got to be carrying them in their mouths! Imagine stuffing your mouth full of thistle seeds and then scurrying over the ground and up a tree before trying to spit all that stuff out again. Think about what it feels like to have a hair in your mouth and the sound and faces you make as you try to dislodge it. Now imagine the same sounds and faces on an adorable little mouse trying to spit out an entire mouthful of thistle fluff, which has to be far more worse than hair. This is the lasting imagery in my head, and I can’t tell whether I should be laughing or feeling regretful for screwing up the results of all that effort.

I really do feel badly about disturbing all those mice, though at least the weather was really nice as they sought shelter elsewhere. Hopefully, all the mice made their way back to those nests and didn’t mind that the host trees were now oriented horizontally instead of vertically. But while I feel bad about (temporarily?) dislodging them, and while I know it’s not nice of me at all, I’m even more distracted by what sound those mice must have made when they tried to spit out all those fluffy seeds…

‘Phleh! Phleh! Phleh!!’

Originally posted in The Prairie Ecologist.