Butterflies: They flutter best when the heat’s on

Published 12:05 pm Friday, June 10, 2016

The swallowtail had its wings spread out on the orange marigold, a not particularly safe place given the bird feeder a few feet away. Resting? Injured? At any rate, it wasn’t in a protected place. Had I been inclined, I could have reached out and touched it. Butterflies generally fly away at the first sight of danger, a moving body, a shadow.

It was a pale swallowtail. Butterfly books generally describe the upper surface of the wings as black and creamy white. This one, however, was black and white, the same as in many other photographs. It has been described as the only black-and-white butterfly in the Northwest.

One of the largest butterflies in this area, the pale swallowtail has a thick black wing border, black stripes, a pointed forewing and a few tiny blue and reddish-orange splashes of color toward the rear.

Butterflies are cold-blooded, which means that internal temperatures vary with external temperatures. Their own metabolism doesn’t generate enough heat/energy to fly. Like snakes, cooler weather turns butterflies sluggish, and it’s that sluggishness that makes them more vulnerable to predators such as birds, lizards, wasps, frogs and even spiders.

Dragonflies will eat butterflies, too. Many predators also eat the eggs and caterpillars.

Let’s return to the pale swallowtail on the orange marigold on the east side of the house. The temperature was about 60 degrees in the early evening. While I was taking a photograph, it slowly raised its wings vertically as if to take off, but they remained upright, then returned to flat a minute later.

My unscientific conclusion: the pale swallowtail had to land because the temperature had dropped to a level where flying wasn’t an option. The prey-vulnerable site might have been the best it could do as muscles failed to deliver it to a protect place. Raising the wings while I was there may have been an attempt to fly away from perceived danger.

In the morning it was still there, but shortly after the sun’s rays hit its spot, it flew away.

Here’s a sample of temperature-related butterfly science:

Danish researchers have found that butterflies in Greenland are shrinking in size in response to increasing temperatures. They measured the length of about 4,500 individuals collected between 1996 and 2013 and found that wing length has decreased significantly, at the same rate in two test species, and whether male or female.

Recent British research has shown that certain species of moths and butterflies are becoming more common, and others rarer, as they are affected by climate change. Conservationists had assumed that a warming, drier Britain would be good for butterflies and moths but research shows that some species of the 155 studied may already be declining.

Butterflies are emerging in spring more than 10 days earlier than they did 65 years ago, a shift that has been linked to regional human-induced climate change in an Australian study. It establishes, for the first time, a causal link between increasing greenhouse gases, regional warming and the change in timing of a natural event.

Columnist Sharon Wootton can be reached at 360-468-3964 or www.songandword.com.