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!
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.
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?
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.