WHIT GIBBONS’ ECOVIEWS: Are butterflies disappearing?
Q: A tornado took down all the shade trees in my yard. Since that time I have had two successful seasons of wonderful butterfly gardens frequented by as many as 20 different butterflies at a time. This year, however, I have only seen six all season. I know that some butterflies are endangered, but I never expected such a significant and precipitous decline.
Our climate has been very odd this year, with unusually cool and cloudy weather far into the spring and even summer. Many of my flowers have bloomed an entire month later than normal. Now, many of the plants I set out specifically to attract butterflies have run their course and, still, no butterflies. On two recent trips to south Alabama, I made careful notes of the few butterflies that I saw. Very few. So, it’s not just my area. What insights do you have about this situation?
A: An environmental paradox is that on average about half of the populations of any native species decline in number each year. The reason is that the size of a local population of any organism (deer, turtles, dandelions) depends on how many individuals are born or immigrate to the area versus how many die or emigrate. Since, under natural conditions, no species (other than humans) remain in a state of overpopulation for many generations, declines in animal and plant populations must be in proportion to their increases. Thus, constantly fluctuating population numbers are the norm, although the reasons may be undetermined. Ecologists often speculate about the whys and wherefores of declines or unusual abundances of particular species, with the weather being a common explanation, but sometimes we are just guessing about causes.
Last month I heard that fireflies were declining. Apparently some people think they are not as common in certain areas as they have been in recent years. After I was asked about the possible lightning bug decline, I began to wonder if it were true. That night, my backyard was full of them for the first time in the season. As for butterflies, I checked with an entomologist colleague to see if a butterfly decline has been noted in the Southeast or elsewhere.
I asked Karl Espelie, University of Georgia professor of entomology, if butterflies were thought to be disappearing. According to him and several other faculty members “the general consensus is no: butterflies are not disappearing. Joe McHugh has been teaching insect taxonomy at UGA for 20 years and has seen no change in the diversity of butterflies in the collections that the students turn in.” However, Karl noted that “the disclaimer would be that there are certainly areas where the habitat has changed dramatically, and in those places there may be fewer butterflies, as well as other species, than there were a few years ago.” Some species of butterflies “feed on a very narrow range of host plants.” Butterflies “might be more likely to suffer when those plants they depend on decline or disappear.” Also, “various factors” implicated in the “colony collapse disorder in honey bees could certainly be affecting other species of insects as well.”
Karl pursued the butterfly question with scientists outside of the UGA entomology department. “Jerry Payne, a retired USDA entomologist in Byron, Ga., takes part in butterfly counts each year and says that the changes are regional and dependent on habitat destruction. Jim Porter in the UGA School of Ecology claims that some of the butterflies that he collected when he was a kid in Ohio are no longer there or at least that some of them are not as common.”
So, even among the experts, the status of butterflies is equivocal. Although extinction of most or maybe any butterfly species may not be imminent, signs of permanent declines are suspected at some localities as a result of environmental changes. Whatever the long-term situation in your region and nationwide, let’s hope butterflies will be back in full force next year or perhaps even this autumn.
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Whit Gibbons is an ecologist and environmental educator with the University of Georgia’s Savannah River Ecology Laboratory.