During the summer of 2018 there was a phenomena which illustrated how much there is to learn if you keep your eyes open. About the end of June I started to see some regal fritillary (Speyeria idalia) butterflies. It seemed a bit early, but May and June had been warm. The black samson (Echinacea angustifolia) they like to nectar on was beginning to bloom already, so the phenology was appropriate to the year.

The next week when I returned to my prairies all hell had broken loose. Everywhere I looked I saw regal fritillaries. They were feeding on a variety of blooms; they were wafting around at eye level, flipping past my head as I walked around; they were all through the sky as far as the eye could see. At any time I could look up and see twenty or thirty fritillaries across my field of vision. Where the hell did they all come from? What were the important weather events to allow excellent egg deposition and survival the previous fall, allow overwintering of early instar larvae, allow sufficient violet growth to feed those larvae during the spring and allow efficient pupation to create the clouds of butterflies I enjoyed that summer? What was the ultimate cause of the population explosion?

The cheap answer is that the flapping wings of a butterfly ultimately causes a typhoon in the Pacific, the chestnut from chaos theory. Everything is contingent upon everything, a chaotic system impossible to fathom. The other extreme we are prone to is to attribute a phenomena to a single, simple cause. A facile oversimplification is almost always wrong. The fritillary outbreak was undoubtedly due to more than one factor. So let’s go through the list.

First, late summer and fall weather was pretty gentle in 2017. There was enough rain and a warm enough fall for good plant growth. The winter was fairly open and gentle until a cold wet April added 20” of snow. While there are always some violets (Viola pedatifida and Viola nuttallii) in our hills, neither I nor my neighbors (I do a little trespassing to look around now and then) had an unusual amount. If you had asked my opinion that spring on the potential for a fritillary outbreak I would have guessed that populations would be down because of a lack of snow cover in midwinter and the crappy April. What happened?

Well, here’s my guess. What stood out in 2018 as unusual was that when it finally warmed up at the end of April it stayed consistently warm in May and June, with good moisture. Cool season plants that had been languishing on April 25th absolutely detonated in May. Temperatures at the nearest weather station near Watertown were 6.3 degrees above average in May and 4.5 degrees above average in June. Add in the moisture from the April snows and the spring rains, and even the gravel hills looked like gardens. Certainly other factors were important as well. Perhaps disease or parasitism or predation were less significant than average. Maybe the warm weather limited fungal disease of the larvae or the pupae. I don’t know. What I do know is that the weather conditions of 2019, when another cold, snowy April turned into a cold damp May, led to a dearth of regal fritillaries. They were hard to find this past summer, though I saw a few. Where did contingency lie? It is fun to consider

Postscript

As I have written earlier, one impetus for this project was to provide habitat for Dakota skipper butterflies. Providing habitat for regal fritillaries was not something I had considered in designing my seed list. After the fritillary outbreak I purchased prairie violet (Viola pedatifida) seed as well as whorled milkweed (Asclepias verticillata) seed (I had noticed adult fritillaries nectaring on whorled milkweed) to spread last spring. While the future for Dakota skippers is pretty dicey, regal fritillaries seem to have more resiliency, or perhaps less specificity in habitat requirements. It pleases me greatly to add another species of conservation concern to my habitat plan. Perhaps, if it is a better spring, I will see one using the restoration this summer.

Again and again it strikes me how much I have to learn, and that much of learning is simply spending time in the prairie with my eyes open. In the immortal words of Ferris Bueller: “Life moves pretty fast. If you don’t stop to look around once in a while you could miss it.”