The Butterfly Effect

Late last September I noticed a cloudless sulphur butterfly ovipositing on a privet senna. (Privet senna used to be called Cassia ligustrina, but now has been reclassified as Senna ligustrina). Not long afterward I found 4 big healthy caterpillars busily eating the flowers, and one small caterpillar on a privet senna around the corner. I'm always excited to see caterpillars, but this time was special because it was the first time I had seen sulphur caterpillars in our yard since Hurricane Charley gave us a near miss in 2004! (We weren't quite so lucky with Wilma in '05, and Irma in '17).

Cloudless Sulphur Caterpillar on Privet Senna

I've seen only the occasional large sulphur in our yard since Charley, and certainly none none laying eggs.  At the same time, I have cast many an envious glance across the canal, where sulphurs frequently visit the red flowers in that neighbor's yard. And I haven't seen the gorgeous orange-barred sulphurs at all for years.

Orange-Barred Sulphur
Female: Top & Middle; Male: Bottom

Sulphurs don't have it easy. Once as I was sketching a newly-emerged cloudless sulphur dry its wings, an anole jumped out of nowhere and snatched it right off the chrysalis shell. The caterpillars don't seem to be toxic, so they would be vulnerable to birds. Years ago I observed a tiny spider -  sucking on a hapless sulfur caterpillar many times its size. I went back a few hours later to see how much the spider had expanded, but couldn't find it or any traces of the caterpillar. The spider either stowed its prey somewhere better hidden, or perhaps both got taken by a bird. I didn't see how the spider could injest the whole caterpillar in one go without exploding!

You Can Just Make Out the Spider in the Top Right
Cloudless Sulphur Caterpillar on Bahama Cassia

I've always blamed the hurricanes along with habitat loss for the disappearance of the sulphurs in our yard. And indeed, the entire insect population visiting us has declined significantly in both numbers and number of species over the years. But that really doesn't explain why there are sulphurs across the canal, and not here, or why I still get other butterfly species reproducing in the yard. It also doesn't explain why I got plenty of the smaller barred yellow sulphurs once I introduced their larval host, pencilflower. (Stylosanthes biflora).


A little reading and a little web surfing has led me to something of an aha! moment, and a no-brainer at that. I came across a post by Florida wildflower specialist Craig Huegel, in which he commented that he never had seen sulphurs ovipositing on cassias that weren't blooming. He also wrote that he preferred Bahama cassia over privet senna because it blooms more regularly, while privet senna blooms in sporadic flushes. It turns out that the orange-barred sulphurs prefer Bahama cassia over privet senna as well. (Bahama cassia now seems to be classified as Senna mexicana var. chapmanii).

Newly-Emerged  Female CloudlessSulphur(I think)
Blue Porterweed, Stachytarpheta jamaicensis

As the photo with the spider shows, I had Bahama cassia at one time, but it wasn't in a good place. Over time it declined, and then died. Once you've had privet senna in a no-lawn yard like ours, you'll always have it, due to its vigorous self-seeding. I like the plant for the bamboo-like effect its dark green, pointed leaflets, as well as its striking deep yellow flowers.

It's supposed to be drought-tolerant, but it is short-lived for me. Maybe it is just too hot, sunny and salty for it here, or maybe I just don't love it enough. Over the years I've pretty much abandoned it as a garden plant, letting it grow in the waste places in the yard where nothing else thrives. Of course, it gets ratty quickly, and then I cut it down. If I were a sulphur butterfly I wouldn't lay any eggs on its desiccated leaflets either. So without thinking about it consciously, I've stopped providing reliable host plants for the large sulphurs.

Privet Senna - Senna ligustrina

Another thing that I did along the way was remove a large firebush (Hamelia patens) that was growing in absolutely the wrong place. It was a great favorite of the sulphurs, who like the same flowers that hummingbirds do. It also gave cover for birds, and mockingbirds and red-bellied woodpeckers loved its berries.

There's no guarantee that I'll get a resident sulphur population again, but it's worth trying. I can't do anything about hurricanes or the overbuilding, but I can get a Bahama cassia, take care of the privet senna, and see about finding a place for another firebush. It's so easy for one seemingly small action to set a chain reaction in motion. As former Florida senator and governor Lawton Chiles once said, "The knee-bone's connected to the jawbone."(He really did say that).