Many butterfly watchers across Pennsylvania, even those with pollinator or butterfly gardens or fields packed with butterfly-attracting wildflowers, have reported a noticeable decline in the big showy butterflies like monarchs and swallowtails, this summer.
Some have seen a bit of a resurgence in their backyard butterfly numbers later than normally expected in the past couple weeks. But overall summer 2020 has seen fewer butterflies in many parts of Pennsylvania.
The drastic decline in monarchs was expected after the Center for Biological Diversity announced that the winter 2019-20 population of the species in the central Mexican mountains where all monarch butterflies east of the Rocky Mountains spend the winter was less than half of what it was the previous winter. They also noted that it was less than half the population that scientists believe is needed for the species to avoid extinction.
Monarch butterfly on butterfly weed. (Photo by Jerry Hassinger)
But species like the eastern tiger swallowtail, great spangled fritillary, red spotted purple and orange sulphur do not migrate. Any decline in their populations in Pennsylvania would be caused by conditions right here at home.
“The people I spoke with concur that there was definitely a drought of butterflies for most of the spring and summer,” agreed Hazleton’s Rick “The Butterfly Guy” Mikula, president of Butterfly Rescue International and consultant to both the Association For Butterflies and The International Butterfly Breeders Association, of which he was a co-founder and president.
“Then about three weeks ago we had an amazing explosion of all butterflies to the point that our garden looks like a Disney movie. "
He believes the “overly hot summer” may have played a part.
“Many species, including monarchs, will go into a shut down when temperatures get too warm. Monarch eggs do not hatch in very dry conditions and dry weather can also kill milkweed.
“There are several studies that have shown that temperatures above approximately 95 degrees Fahrenheit can be lethal to all stages of development and adults are incapable of mating. So that could explain a slow start. Now the sudden explosion of butterflies makes you wonder about the validity of the studies.”
Spicebush swallowtail (Photo by Jerry Hassinger)
Jerry Wiedmann, lead organizer of the Ohio Lepidopterists Butterfly Monitoring Network, the second oldest network in North America, noted, “This has been a bad year for butterflies in our area. The late cold spring is one reason. The ongoing downtrend in butterfly populations is another.
“Certainly, habitat loss and habitat fragmentation are contributors to the long-term downtrend. Plant timing due to global warming may have a negative effect on some species.”
He cautioned, “Butterfly populations are cyclic and if several of the big, visible species all have a bad year at the same time it really looks even worse than it is.
“Numbers have been way down in all of the survey work that I am aware of this spring/summer. Weekly monitoring and July 4 (one day) counts as well. I am seeing some evidence of recovery in the last couple of weeks with second and third brood butterflies emerging now.”
Michael Skvarla, assistant research professor of arthropod identification at Penn State, offered a somewhat contradicting view, at least for the short-term.
“As far as a decline in butterflies,” he said, “this is the first I’ve heard anyone asking about it. I haven’t noticed any decline in State College and am seeing perhaps more butterflies this year compared to years past. They’ve been going absolutely nuts for the joe-pye weed we have for the last two weeks or so.”
But, he cautioned, “That being said, there does appear to be a worldwide decline in insects and specifically drops in the number of moths in eastern North America. The reasons for these drops are multifaceted and including things like habitat loss and fragmentation, use of pesticides, and climate change.”
Red spotted purple butterfly on buttonbush. (Photo by Jerry Hassinger)
Looking forward from conditions this summer, Mikula said, “It would be almost impossible to project if this is a blip or long-range effect. There are too many factors to take into consideration.
“Next year’s recovery of monarchs depends mostly on the temperature in a 10-14-day period in southern Texas next spring. If it is too hot or too cold, they can’t lay eggs when returning from Mexico. A few years ago, the spring stayed too cold for milkweed to flourish early enough for the returnees to find anything to lay their eggs on. So, to project a recovery is stifled by too many variables such as snowstorms or continued habitat destruction in the over wintering sites.”
Wiedmann said, " I would really like to see a warmer April and May next year to see how much of an improvement that would bring. We have had several cold springs in a row.”
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Contact Marcus Schneck at mschneck@pennlive.com.