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LEPS & ODES: Butterflies have 'dynamic' population fluctuations

The 1,020th and final Painted Lady was also the last butterfly of the 2017 season at the University of Minnesota Biological Station at Itasca State Park. Painted Lady was the most common species in 2017, but none were observed in 2018. (Photos by John Weber/For the Enterprise)1 / 2
The 3,508th and final Clouded Sulphur was the last butterfly of the 2018 season. It was the most common species this year. 2 / 2

Now that white snowflakes have replaced the green leaves of summer, I'm pausing to reflect on what I witnessed during the 2018 butterfly season. To use the song title, "It was a very good year."

On the one hand, the total 9,227 butterflies in 2017 dropped ever-so-slightly from the 9,253 I had in 2016. A dramatic surge to 13,914 happened this year. There was an impressive gain of 4,687 individuals — more than 50 percent higher than 2017.

I'll try to convey the impression these 13,914 butterflies made on me using relative few words and numbers. I feel looking at the butterfly families largely explains the dynamics at play in 2018, so I'll proceed along those lines.


These five butterfly families accounted for 2018's net increase:

• Checkerspots/Crescents. Northern Crescents were a major contributor to the 301 individual increase for this family.

• Fritillaries. The 466 increase was divided among the Speyeria (genus of larger fritillaries) and the smaller Meadow Fritillary.

• Skippers. European, Northern Broken-Dash and Dun Skippers contributed the majority share of the 1,036 increase.

• Monarchs. They enjoyed an even greater increase — going from 321 in 2017 to 1,370 adults this year. In my Oct. 20 column, I had projected 1,569 would be exceeded in 2018. Though they fell short, it was still an impressive increase. Their season that had been sizzling, suddenly fizzled to an abrupt, early end.

• Sulphurs. Clouded Sulphurs propelled an amazing 3,174 increase for this family of yellow butterflies. They were the most common butterfly of the 2018 season. In fact, by late season they were almost as numerous as falling autumn leaves! This was especially true at alfalfa hay fields, where their number were virtually uncountable. Though mind-boggling, I did give it my best shot!


The above five families produced a gain of 6,026 individuals compared to 2017. This was offset, somewhat, by two families with a combined loss of 1,331.

• Satyrs. A decline of 377 was largely attributable to fewer Eyed Browns and Little Wood-Satyrs.

• Vanessas/Ladies. There was a decline of 954 because no Painted Ladies were present in 2018. I had tallied 1,020 in 2017, making them, by far, the most common butterfly species on the wing last year. They were the most common butterfly that fall, far outnumbering migratory monarchs. (Not a great feat given the few monarchs I witnessed flying south to Mexico in 2017.)

So what happened to Painted Ladies? Spring rains in southwest U.S in 2017 produced an abundance of flowers that fueled a flood of Painted Ladies spreading northward. By this spring, drought returned to the southwest. (Even wild mustangs there had a tough time finding forage.)

So I'm not surprised I had no Painted Ladies in 2018. Afterall, no stage of their development can withstand freezing temps. They have to originate from elsewhere where it remains a bit warmer.

Absent 2017, present 2018

These 11 species showed up: Checkered White, Western White, Henry's Elfin, Melissa Blue, Greenish Blue, American Snout, Bog Fritillary, Pearl Crescent, Tawny Crescent, Question Mark and Two-Spotted Skipper. These were the hidden gems of the 2018 season. Altogether, only a total of 21 individuals were observed. Though few in number, they produced a season of surprises, as I termed our 2018 count season in my overview that ran Aug. 18 in the Enterprise.

Butterflies, as insects can and do, have very dynamic population ups and downs. These butterfly families that a so-so, lukewarm season in 2018 could have a breakout year in 2019: Swallowtails, Whites, Coppers, Hairstreaks, Elfins, Anglewings, Tortoiseshells and Admirals.

Who knows? Stay tuned.