A Tough, Adaptable Survivor

In North America, there are lots of prairie species of conservation concern. Plants and animals that used to be more abundant and widespread than they are today are being squeezed by habitat fragmentation and degradation. On the other hand, there are also prairie species that are adapting very well to recent changes in the landscape and climate. We spend a lot of time worrying about the former. Let’s spend a few minutes celebrating one of the latter!

Orange sulphurs are more abundant today than they were 100 years ago.

The orange sulphur butterfly, also known as the alfalfa sulphur (Colias eurytheme), is one of the most abundant butterfly species in North America. It can be found through most of Mexico and all the way through much of Canada and Alaska. The species is variable in its appearance and there are many other yellow butterflies that look similar, are closely related, and that may even hybridize with the orange sulphur. That makes identification in the field very difficult.

If there’s any orange color in the wings, that’s probably an orange sulphur. If not, good luck. I think all the photos here are of orange sulphurs but I won’t be surprised or upset if someone points out that one is a clouded sulphur or something else.

The patch of orange on the top wings is a nice characteristic to look for when trying to identify orange sulphurs.

Getting away from mundane identification characteristics, the orange sulphur is a survivor and should be given credit for that. As other butterfly species have lost population size, the orange sulphur has increased its continental population significantly. Other species are found in few places than they used to be. The orange sulphur has apparently expanded its range (especially to the east and north) to fill up the continent. It doesn’t overwinter well up north, but can move northward each year from the south. Climate change seems likely to make that even easier in the future.

Why is the orange sulphur doing so spectacularly well? One reason is that its larva like to eat legume species, including lots of new ones we have introduced to North America. A big example is alfalfa (Medicago sativa), which the caterpillars really love – to the point where the orange sulphur is sometimes considered an agricultural pest in alfalfa production fields. Larvae also like to feast on sweet clover (Melilotus sp) and white clover (Trifolium repens), among many others.

There has to be more to the success story than just lots of food, though. Lots of other butterflies have abundant food sources but are experiencing population declines. Several prairie skippers that are rarely seen anymore use common grass species as larval hosts. Those grasses are everywhere – the butterflies are not. What else is the orange sulphur doing to thrive in a rapidly changing world?

I don’t know the answer to that. If we could figure it out, it might help us understand how to help other butterflies that aren’t doing as well as the orange sulphur. Habitat loss and fragmentation seem like obvious drivers of butterfly population declines, but again, those rare skippers – and other declining butterfly species – are often doing poorly even in parts of the continent where their prairie habitat seems relatively intact. Something else must be going on.

Pesticides are often listed as a major contributor to insect declines, and that seems fair, but a lot of orange sulphurs live directly in and around agricultural crop fields, where those pesticide effects should be highest. They also feed on white clover, which is abundant in urban yards where pesticide use can be very intense. Why are orange sulphurs still flourishing?

Here’s looking at you, orange sulphurs!

Regardless of the reasons, the orange sulphur seems to be doing great and we should be happy about it. It’s an objectively gorgeous butterfly, after all, and easy to spot and admire in the field. Despite that, I’ve occasionally caught myself occasionally thinking “Oh, that’s just another orange sulphur” when one catches my eye. A totally unfair response. Birders do the same thing, I know, with species like northern cardinals, American robins, or other species that have adapted well to our contemporary landscapes. We get numb to the beauty we see everyday.

We should be lauding the resilience and adaptability of these abundant native species. The fact that they’re common is a good thing, right? I guess white-tailed deer might be an exception to that rule. Their population numbers have skyrocketed since the early 1900’s and they are now causing considerable damage to ecosystems (and cars). Ok, fine. We have too many white-tailed deer. To my knowledge, no one has ever had to buy a new car after hitting an orange sulphur on the interstate. Let’s give these handsome butterflies a break and acknowledge their achievement!

In the movies, the tough, adaptable, resilient characters are the ones we root for. We should probably root for them in prairies too, huh? Abundance is a good thing. It’s not like orange sulphurs are stepping on the heads of other butterflies as they fight their way to the top. At least, not as far as I know. (Are they? Surely not.) Assuming they’re just finding ways to survive and doing it well, let’s all agree to celebrate their success. Maybe we can even figure out how orange sulphurs are doing it and see if there’s anything we can apply toward the conservation of species that aren’t thriving.

Photos of the Week – November 11, 2022

Back on October 29, I spent a lovely couple hours across town at Lincoln Creek Prairie. I arrived a little before sunrise and had a little time to scout before the light arrived. That meant that when the sun finally popped above the horizon, I had a couple different subjects picked out to put in front of it. After that, I wandered around trying to find insects (there were a few, including some I photographed but didn’t include here). In between insects, I challenged myself to find other interesting compositions.

I had a great time.

Common milkweed (Asclepias syriaca) pod and seed at sunrise. Nikon 18-300mm lens @300mm. ISO 320, f/14, 1/500 sec.
Tall thistle (Cirsium altissimum) at sunrise. Nikon 18-300mm lens @300mm. ISO 320, f/14, 1/500 sec.
Switchgrass (Panicum virgatum) at sunrise. Nikon 18-300mm lens @300mm. ISO 320, f/9, 1/1000 sec.
Stinkbug on Canada goldenrod (Solidago canadensis). Nikon 105mm macro lens. ISO 500, f/10, 1/100 sec.
Fly and morning dew. Nikon 105mm macro lens and Raynox 250 magnifier. ISO 500, f/16, 1/60 sec.

The sunlight quickly became intense enough that it was hard to do much with it. That bright light means extreme contrasts and less color saturation, among other issues. I wasn’t ready to head home, though, so I fell back on an old trick. I worked along the edges of the skinny prairie patch, using nearby trees as a kind of diffuser. The dappled light coming through those branches was softer and more pleasing and the scattered shadows helped provide clean backgrounds for macro photos.

Common milkweed seed and morning dew. Nikon 105mm macro lens. ISO 500, f/13, 1/100 sec.
Canada goldenrod (Solidago canadensis). Nikon 105mm macro lens. ISO 500, f/11, 1/160 sec.
Canada goldenrod (Solidago canadensis). Nikon 105mm macro lens. ISO 500, f/9, 1/800 sec.
Canada goldenrod (Solidago canadensis). Nikon 105mm macro lens. ISO 500, f/9, 1/800 sec.
Wild lettuce (Lactuca sp.) Nikon 105mm macro lens. ISO 500, f/14, 1/160 sec.
Lead plant (Amorpha canescens). Nikon 105mm macro lens. ISO 500, f/10, 1/500 sec.

Insects certainly weren’t abundant, but they weren’t absent either. Flies were the most common, but I saw several stink bugs, a milkweed bug, a little larva I couldn’t identify, and even a little skipper. I was seeing a lot of spider silk caught on plants but I didn’t find an actual spider until I was almost back at the truck and ready to go home. I got to watch it work on the beginnings of a small web. I wonder if it finished the web or caught anything. Given the scarcity of insects around, its chances of catching dinner seemed low.

Common checkered skipper. Nikon 105mm macro lens. ISO 500, f/13, 1/160 sec.
Common checkered skipper. Nikon 105mm macro lens. ISO 500, f/13, 1/125 sec.
Stink bug on pitcher sage (Salvia azurea). Nikon 105mm macro lens. ISO 500, f/11, 1/200 sec.
Tiiny spiderling on pitcher sage (Salvia azurea). Nikon 105mm macro lens. ISO 500, f/14, 1/125 sec.

There are insects and spiders active all winter, but not very many. Every time I go out this fall, I see fewer and fewer. This is a challenging time of year for photography, at least for the kinds of subjects I like best. In addition to a drop in insect numbers, the color of vegetation is fading from gold to a duller brown and there’s no been no snow yet, and precious little frost.

Even with all that, I spent more than two hours exploring a tiny sliver of prairie a couple weeks ago and am looking forward to doing it again soon. It’s supposed to be pretty cold this weekend, with temperatures getting down to about 15 degrees Fahrenheit. It’s not supposed to be windy though… Sounds like great conditions for a prairie hike! Who’s with me?