Has there been a drop in the Eastern Black Swallowtail population this year?
I am in upstate New York. The last three years, a friend of mine has been raising Eastern Black Swallowtail butterflies from caterpillars and eggs she finds in her garden. In 2019, she found lots of them in July and August, so much so that she had to buy extra dill at the farmer’s market just to keep them all fed! Last year, she found a few, but nowhere near as many.
This year, she has not found a single black swallowtail egg or caterpillar in her garden, despite providing plenty of dill and other food plants, as well as flowers for nectar.
My observations while out in our local nature preserve seem consistent with this: Last year, for most of the summer I would spot at least one and often several black swallowtail adults on the wing almost every time I went out for a hike. This year, I have seen huge numbers of spicebush swallowtails in flight, but very few black swallowtails. (Since they are both large, dark swallowtails, they can be hard to distinguish, but I have learned to tell the difference as long as I can get a good look at the upperside as they fly past.) (It is possible I’m overestimating the number of black swallowtails I saw last year–I was not as good at distinguishing the two back then.)
We hope our unscientific observations are not an indication of a larger-scale drop in the black swallowtail population, but we’re wondering if there have been any other reports of a lack of black swallowtails this year?