It may be that monarch butterflies and fireflies (“lightning bugs”) are among the general public’s favorite insects. Unfortunately, these popular warm-weather visitors are both under siege, with human fingerprints all over their declining numbers.
I’ve written about monarch butterflies before, in August 2022: “First, the devastating statistics. Eastern monarchs (OUR butterflies), covering most of North America, dropped 84 percent between 1996 and 2014, a startling statistic, unfortunately not very current. Update in July 2022: ‘This population shrunk by between 22% and 72% over the past decade.’ Realizing this is a huge statistical range… these numbers are SIMPLY DREADFUL.” (emphasis mine).
The question is why? My review then indicated it was a blend of factors… climate change, loss of essential milkweed plants, and habitat destruction of overwintering areas, in Mexico, which was halted years ago. Now, NEW insight from a study on butterflies in the Midwest, published June 20th (very current). Agricultural insecticides exerted the biggest impact on the size and diversity of butterfly populations in the Midwest between 1998 to 2014. Quoting the New York Times: “Especially detrimental, researchers found, was a class of widely used insecticides called neonicotinoids… absorbed into the tissues of plants.”
Researchers in the new study integrated multiple data sets and used statistical analysis to make comparisons between different potential drivers of decline across 81 counties in five states, including Iowa. They found that in the median county over the 17-year study period, pesticides were associated with an 8 percent decline in butterflies. For monarchs, however, this drop was a much larger 33 percent.
Climate change isn’t the only factor that appeared less significant in this research than might be expected. In a result that seems surprising (it was to me), the study did NOT find new declines in monarchs from the use of glyphosate, a herbicide commonly sold under the brand name Roundup. Glyphosate eradicates milkweed, the only food source for monarch caterpillars. Its use is a primary cause of monarch declines. However, the authors note that beginning in the early 2000s, the impact from glyphosate “largely disappeared since the largest decline in milkweed had already occurred.” Basically, this impact is already baked into the numbers, but is not behind the more recent drop-off.
So now, fireflies (technically beetles, not flies), where some of the same factors are in play. It’s challenging to get a sense of declining firefly numbers, in part because there are an estimated 2,400 species and they haven’t been studied as extensively as monarchs. According, some sense of falling numbers is anecdotal. Nevertheless, most experts think the firefly population is diminishing, varying greatly based on location. For example, if you live next to a hayfield adjacent to a stream, probably your numbers are fine. On the other hand, if you’re in a housing development with manicured lawns, your numbers are likely to be off.
According to Eric Day, a Virginia entomologist and a firefly expert, habitat destruction – primarily housing and commercial development – is the greatest cause of firefly loss. A surge in artificial lighting is another negative factor… and yes, climate change is also problematic. But, according to Day, there’s some good news regarding fireflies. “I would say fireflies are THREATENED due to habitat loss, but they are not going extinct. Some are adapting in different regions.” In other words, hey, it could be far worse.
Several closing thoughts. Monarchs and fireflies are two different “canaries in the coal mine;” if their populations are diminished, what lesser-known insects might also be imperiled? Furthermore, it seems obvious if modern society will not or cannot ensure their long-term survival, the guilty finger must be pointed back toward ourselves.
Finally, more optimism, from Anna Walker, part of the International Union for Conservation of Nature: “When there’s a will to protect species, we can be quite successful, especially with insects because they reproduce very quickly. As long as you can protect or restore their habitats, we’ve got a really good chance of reversing firefly declines.”
I trust something similar can be said for monarchs. For both insects, let’s both hope… AND act.
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I’m pleased to be part of the Iowa Writers’ Collaborative. These are my colleagues:
Thanks for pointing out the loss of habitat for insects. For monarchs in particular, their over-wintering sites are in great jeapardy. And while we plant milkweeds in our ditches, if they are planted next to agricultural fields, the chemicals will be absorbed into the milkweeds and poisoning the catepillars who eat them. It's such a wide-rainging subject.
Neonicintinoids are also implicated in a decline of aquatic invertebrates which is detrimental to the web of life, including one of Northeast Iowa's blessings; trout fishing. some states are beginning to recognize the threat of "neonics" and New York, New Jersey, and Maine have total or partial bans on them. Thanks for your awareness.
Steve M.
Decorah