Is a butterfly apocalypse descending on Evanston?

“I don’t see as many butterflies as I did when I was a kid” is a complaint Doug Taron hears all the time. He sometimes feels that way himself. But as an entomologist (an insect scientist) and the curator of the Istock Butterfly Haven at the Notebaert Nature Museum in Chicago, Taron has to treat the issue rigorously. Is there evidence that butterflies are in severe decline, along with many of the insects at the base of the food pyramid that wild things depend on?  Or do people just remember a few really good days for butterflies when they were young?

Taron leads the Illinois Butterfly Monitoring Network, a citizen science project that has run for nearly 40 years, building a data set that backs up a pessimistic answer. In 2018, the New York Times called the idea of an insect population crash “the insect apocalypse.”  Taron is worried that we’re seeing it play out here in Evanston and across Illinois.  

Taron spoke on May 14 to an audience of more than 50 as part of Nurturing Nature, a series of monthly speakers on environmental topics co-sponsored by Natural Habitat Evanston, Rotary International, Evanston Public Library and the Evanston Ecology Center. He offers some reasons for optimism – a single butterfly can have dozens or even hundreds of offspring. A small winter population of monarch butterflies in Mexico can rapidly build back its numbers if weather is favorable and milkweed plentiful as they migrate to the Midwest in the spring. This spring, species like red admirals and painted ladies are having boom years.

There are even examples of species reliant on narrow or vanishing ecological niches that have reversed their declines. One is the regal fritillary, a gorgeous black, white and orange butterfly that thrives in recently burned prairie but needs an unburned refuge.  Only large expanses offer this balance of habitats. Once widespread, it had nearly vanished east of the Mississippi River. But a small, fragile population in northwest Indiana surged after restoration of prairie lands there. From that base, it is recolonizing Illinois prairies.

Yet the overall trends are worrisome. Monitoring network volunteers walk fixed routes for a measured amount of time in dozens of preserves and parks in the area. They’ve amassed nearly 1 million butterfly sightings. Each year, they collectively walk monitoring routes more than 1,000 times, providing so much data that the results are more than anecdotal. The declines they show are real.

Smaller booms, bigger busts

Boom year populations for most species are smaller than they were. Bust year declines are steeper. From 2000 to 2018, the average number of butterflies a monitor saw in an hour of searching went from 44 to 30.  Almost every year, one fewer butterfly than the year before.  

The early part of the last decade seemed to be a turning point locally.  At Bluff Spring Fen, a preserve near Elgin that Taron monitors, populations bounced up and down till 2010.  But every year since then, his counts have been below the long-term average for the preserve. In Kane County, the trend turned uniformly downward in 2014. Across the Chicago metro area, 2013 was the pivot. Taron has pulled the data apart in various ways. He looked at the cabbage white, the most common butterfly in the area, accounting for 35% of all butterfly sightings. And he looked at all species except the cabbage white.  Was an unusual decline in this one species skewing the results? In fact, cabbage white sightings have been falling at about 3% per year, closely matching the decline in other species.

What can be done?  Taron sees no easy answer. He believes there are multiple causes for the decline, notably widespread loss of high quality prairie and other habitats. But he suggests starting simple. People who develop a special interest can think about “host plants,” the particular species that a given caterpillar requires, like milkweed for monarchs. But anyone with a yard can add native wildflowers like asters or coneflowers to provide nectar for butterflies and pollen for bees and other pollinators.

The Nurturing Nature speaker series will continue 6:30 p.m. on July 9 at the Rotary Center, 1560 Sherman Ave. (also on Zoom), when Larry Heaney, the Negaunee Curator of Mammals at the Field Museum, will speak on “Urban rats: How to manage them and let wildlife thrive.”

Climate Watch is a series of occasional articles about what climate change means for Evanston and what we are doing locally to make a difference.