We all know that April showers bring May flowers. But what do May frosts bring? I don’t know but I know May frosts do not bring butterflies! Two years in a row our normal June bump in the butterfly population did not happen. I have been thinking about why the bumps did not happen. I was suspecting late cold fronts had something to do with it. So, I plotted our butterfly data against Columbus, Ohio weather data and think I have made a discovery.

Above is a chart that shows our June butterfly transect count (in blue). It also shows the number of May days in which the overnight low temperature was under forty degrees (brown bar). As you can see, years in which there were zero May days under forty degrees led to much better butterfly numbers in June. The year 2021 eventually ended up being our best butterfly year of all, as the population rebounded strongly in July. In 2020, the butterfly population did not really rebound until August of that year and finished the year fourth of the five years represented.

Total butterflies counted each year:

2017 - 280

2018 - 392

2019 - 531

2020 - 355

2021 - 544

What Do We Do About It?

There is not a whole lot we can do about this phenomenon. Of course, we have no control over weather. For folks with smaller butterfly garden plots, you can cover beds to give a little protection from these late cold fronts for any caterpillars or chrysalises in the bed. With large tracts of land dedicated to butterfly habitat, like Butterfly Ridge, pray is about the only thing that you can do.

As humans, we have become so accustomed to defying the consequences of weather. We have air conditioners for when it gets too hot, and furnaces for when it gets too cold. We can make snow when the ski resorts need a topcoat. We can seed clouds when it gets to dry. I think the negative effect that late cold fronts have on butterflies is something we are just going to have to tolerate.