By Pepper Fisher
PORT ANGELES – One of North America’s most recognizable butterflies is having a banner year this summer, appearing at local gardens and flowerpots in huge numbers right now.
The large, bright yellow and black wings of the Western Tiger Swallowtail are hard to miss, often compared to the better known Monarch butterflies. David James is an Associate Professor of Entomology at Washington State University. Part of his work is to track Monarchs with the help of citizen sightings, and he faces a problem with people confusing the two.
“It’s interesting you mentioned the Monarch, because so many people on the west side, in Seattle in particular, confuse Monarchs with Western Tiger Swallowtails. And that’s been a particular problem this year because we do actually have a reasonable number of Monarchs this year, more than we’ve had for the last four years. But I have to be careful on the reports because most of them turn out to be Western Tiger Swallowtails. People just see a yellow and black butterfly and automatically think it’s a Monarch. And of course, Monarchs are orange and black. So, I’m forever telling people, it’s orange and black for a monarch and yellow and black for a Western Tiger Swallowtail.”
Another big difference between the two is that Monarchs are famously migratory butterflies. Many of them breed here in the northwest, but they fly thousands of miles south every year for the winter. Tiger Swallowtails spend the winter right here where they were born. In fact, the ones you see in your garden were likely born very nearby, as their range is generally only a mile or two.
So, why are we seeing so many this summer?
“The issue of why they are so common this year, it basically is, I think, down to the fact that the summers on the west side are a lot better these days, or for the last couple of years anyway, then they historically may have been. And these butterflies thrive on sunshine and relatively warm temperatures, and they need those conditions to reproduce and lay their eggs and produce a population. And this is in contrast of course, to a lot of butterflies that are not doing very well, their numbers are declining. And so, it’s good that this butterfly, that is one of the largest in the western US, is actually doing very well.”
With the butterflies breeding now, their eggs will soon grow into large, green caterpillars with two yellow spots on the front, meant to mimic eyes and scare off predators. They’ll overwinter as a chrysalis on the trunk of a tree or even on the side of your house, and we’ll see a new population next year.
James says, more butterflies this year will obviously produce more big, plump caterpillars, and because they’re so big, they’re a very good meal for birds and other predators, so we can expect the usual fluctuation in the population.
Before we ended our call, we asked Dr. James about recent reports of the decline of Monarch butterfly populations, less common in western Washington than on the east side of the state where he lives.
“They’re actually doing very well this year, and I did predict that myself a year or so ago, that they were going to rebound again. And they’ve done that with gusto. I mean the numbers are higher in the Pacific Northwest than they’ve been for four years. So yeah, it’s great. Great news. And we’re getting a few from the west side too, where they’re always much less common because you don’t really have much milkweed over there. But yeah, there’s a few around on the west side too. So you might have one turn up in your garden as well.”
The bottom line is, things appear to be looking up, at least for these two high-profile visitors to our flowerpots. So, let’s enjoy them while they’re here.
“It’s rare for the butterfly to be as common every year. You know, it fluctuates. As you said, some years it will be common and next year may go down a bit, and then they’ll come back again. So, but overall it does seem that they’re doing very well in western Washington now, compared to what they were doing maybe ten, twenty years ago.”