A Tough Plant, Not A Weed

I blame whomever named the plant.  Giving a plant the name “ironweed”, apparently – according to Google – because of its tough stem, creates an unnecessarily negative connotation right from the start.  It’s an unfair connotation for a plant that is both beautiful and important.  It’s also a big favorite of butterflies; something I can attest to after spending a couple hours last weekend chasing monarchs and others around ironweed patches at our family prairie.

Ironweed at our family prairie, growing abundantly in a smooth brome-filled draw.  The abundance of the plant goes up and down each year, but it never spreads beyond the draw or shades out the grass around and beneath it.

There are three species of ironweed (genus Vernonia) in Nebraska, and two that are common in the prairies I am most familiar with.  Both of those – V. fasciculata and V. baldwinii – seem to act in similar ways, but the first likes a little wetter sites than the second.  Both species can occur as scattered plants across a prairie, but are also often found in fairly dense patches where conditions favor them.  That patchy local abundance is the first mark against them by people who don’t appreciate their value.  The second mark is that cattle absolutely refuse to eat them.  This both helps them stand out (especially when blooming) in heavily grazed pastures and helps them spread across those same sites since they gain a strong competitive edge when surrounding plants are all being grazed hard.

Like many other plant species I tend to admire and write about, however, ironweed is not an invasive plant – it’s an opportunist.  It takes advantage of soil and management conditions that favor it, but doesn’t just spread aggressively across pastures.  If you look online, it’s not hard to find websites that encourage its control in pastures.  I dispute that.  At least in my experience, ironweed has its favorite locations (often in draws or other low spots where moisture and nitrogen are high) and pulses in abundance within those locations as grazing treatments and weather vary from year to year.  At our family prairie, ironweed is fairly abundant in some of the low draws where high nitrogen also strongly favors smooth brome, but while there are years when those patches are thicker than others, the overall patch sizes and stem densities of ironweed aren’t any higher today than they were 15 years ago.  That matches what I see elsewhere in central and eastern Nebraska.

(I found a university website online that blamed ironweed for making cattle have to look harder to find grass, thus reducing grazing efficiency.  Give me a break.  That’s the same attitude that leads to people spraying pastures to remove everything that isn’t grass, and then wondering why they need to fertilize their grass and supplement their cattle’s diet.  The same people blame others for the lack of wildlife and pollinators on their land.  …Ok, I’m done ranting – let’s talk about butterflies.)

When I arrived at our family prairie last weekend, I immediately noticed monarch butterflies flying all over the place.  I’d seen a surprising number of larvae back in July, so figured we might have a good August, but I was still impressed with how many adults I saw.  I’m guessing there were 40-50 or more across our 100 acres of prairie.  They kept moving, so it was hard to count them…

Almost every monarch I spotted was either flying or feeding on ironweed.  A few other flowers got attention too, including wild bergamot (Monarda fistulosa), Flodman’s thistle (Cirsium flodmanii), and some early tall thistle blossoms (Cirsium altissimum), but ironweed clearly monopolized most of their attention.  I started stalking monarchs with my camera and eventually found a couple that let me get close enough for to capture reasonable photographs.  While I was doing that, I also spotted myriad bees, along with quite a few other butterfly and moth species.

Here are some photos of the butterflies and moths that were kind enough to let me get close.  I didn’t ever get a good shot of a bee, though there were at least a dozen species feeding on the ironweed flowers, and I also never caught up to one of the many silver-spotted skipper butterflies that were all over the place.

This is one of many monarchs that were floating from plant to plant across ironweed patches last weekend.
I haven’t looked up this moth yet. Maybe one of you can save me the trouble? Thanks in advance.
I’ve been seeing a lot of adult swallowtails around lately, including this tiger swallowtail , which was pretty easy to spot, even from across a large draw.
Ok, this black swallowtail wasn’t on ironweed when I photographed it, but it went to ironweed after feeding on this native thistle.  I was taking bets (in my head) about whether or not the crab spider on that thistle would be able to take down the big butterfly. The butterfly eventually moved within striking distance, but the spider didn’t attack, so I’m guessing it decided to wait for something a little smaller.
Thanks to Neil Dankert, I can tell you that this gorgeous little brown skipper butterfly is a tawny-edged skipper.

Ironweed is too beautiful and important for its name.  Maybe we need a campaign to rename it, and maybe that campaign would help convince people, including those at a certain unnamed university, to leave this plant alone to do its job.  Either way, it might be fun to think about potential names.  Any ideas?

Photo of the Week – August 26, 2011

I photographed these butterflies (numerous photos below) last weekend at our family prairie.  Besides being very pretty, they and the flowers they’re feeding provide an interesting insight into the way biologists sometimes see the world.

Painted lady butterfly near Stockham, Nebraska.

Painted lady butterflies are very common and ubiquitous species found on several continents.  They’re found equally often in prairies and urban gardens, so they’re considered to be habitat generalists.  There’s nothing wrong with painted lady butterflies, but they’re not as exciting for a biologist to see as, say, a Ottoe skipper, which is a rare butterfly that is restricted to native prairies.  There’s an extra thrill in seeing a species like that because of their rarity, but also because the presence of specialist species like the Ottoe skipper can be an indication that a prairie has sufficient size and ecological function to maintain even the most sensitive of species.  Painted ladies are very pretty, but don’t provide that extra little adrenaline rush for biologists.

The butterflies in these photos are feeding on Baldwin’s Ironweed (Vernonia baldwinii) which is similar to the painted lady butterfly in terms of its abundance and generalist habits.  Ironweed is rarely grazed by cattle and so is common in prairies that have been chronically overgrazed to the point where most other wildflowers have disappeared.  It also moves across the landscape easily, so it is often found in old fields (crop land left idle) and other “weedy” habitats.  Many people, in fact, consider ironweed to be a weed, which isn’t really fair since it’s not aggressive at all – it’s just good at filling open space left by intensive grazing, tillage, drought, and other events that reduce the vigor of dominant prairie plants.  While ironweed can exist in prairies that are full of much more specialist and rare plant species, its ability to grow almost anywhere else as well means that its presence is not a good indicator that a prairie is in “good shape” ecologically.

While neither painted lady butterflies nor ironweed are great indicators of whether or not prairies have a full complement of species and ecological processes, both are important components of prairies.  Ironweed can provide nectar and pollen, for example, in prairies that are missing most other wildflower species.  Similarly, painted lady butterflies can provide some pollination services in prairies that might be missing many other pollinator species.  In addition, both species are aesthetically pleasing!  Sometimes it can be hard for biologists to remember how valuable generalist species are – and to step back and enjoy their presence, rather than dismissing them as somehow less important or exciting to see than other species.  There’s clearly much to be admired about generalists.  They’re successful in a world that makes it difficult for many other species to survive.  What’s not to like about that?

Some people probably have a hard time understanding why biologists would have this almost dismissive view of generalist species.  Here’s my best explanation.  Few people would pay to go to a zoo full of species such as squirrels and robins.  Those species can be seen almost anywhere.  Zoos make money because they can show people species like polar bears, pandas, and crocodiles that can’t easily be found elsewhere.  That’s kind of what it’s like for biologists when we see generalist species.  It’s not that we don’t appreciate them (I like watching squirrels in my yard – except when they’re stealing apples from my tree) but we see them all the time.

One of the great things about being a photographer, as well as a scientist, is that I get the opportunity to see the natural world from two different perspectives.  Each helps balance and inform the other and, I think, makes me better as both a scientist and photographer.

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