Why Did Minnesota Polyphemus Moths Emerge in August?
It’s fun to raise polyphemus moths. I hadn’t done it for years but a friend gave me some cocoons last fall so I decided to rear a generation and share the experience with my granddaughter.
At first all went according to plan: The moths began to emerge May 27. Some laid eggs on the 28th and caterpillars hatched 12 days later. I kept a dozen and fed them oak leaves until July 21 when they began to spin cocoons.
Saturday, August 20, 2016
After that I put the cocoons in a safe place where they would be exposed to outdoor conditions until it was time for the moths to emerge in 2017.
However, the plan went awry on August 16 when I discovered a newly hatched male moth in the cocoons’ winter place and another two days later. I hadn't expected this.
According to experts at the University of Florida, “the polyphemus moth is univoltine (one brood per year) from Pennsylvania northward (Holland 1968) and bivoltine (two broods per year) from the Ohio Valley southward (Tuskes et al. 1996).” By this standard, the moths that emerged in August were totally out of line.
Unable to account for this, I asked my friend whether moths from southern stock might have inhabited the cocoons he gave me but he assured me they were Minnesota natives. He also noted that a few of his cocoons sometimes hatch in August but not every year.
So are Minnesota polyphemus moths truly single brooded? If so, why do some emerge prematurely? Do any of these breed successfully? Will climate change affect the life cycle of Minnesota polyphemus moths? Has it already?
Puzzle: Why Did Minnesota Polyphemus Moths Emerge in August?
