‘Very active’ yellow butterfly boom in Washington state

A yellow butterfly with purple wildflowers in the background.
This tiger swallowtail’s tail was probably snipped off by a hungry bird. (Photo by Shelly Hanks, WSU Photo Services)

By Linda Weiford, WSU News

PULLMAN, Wash. – Yellow butterflies almost half the size of a human hand have transformed parts of the Evergreen state into a big garden party.

They’re called tiger swallowtails. And while they’re commonly seen in our region this time of year, more of them are flitting about than usual this summer, said Washington State University entomologist Richard Zack.

“Tiger swallowtails are perhaps our most recognized and beautiful butterflies and they are very evident this summer,” he explained.

Though not as famous as the orange and black monarch, the tiger swallowtail butterfly displays striking black markings across large yellow wings and is a spectacular sight as it flutters alongside roadways or sips nectar from flowers.

An abundance of these colorful winged giants has been reported in parts of the Inland Northwest and on the opposite side of the Cascade Range in the Seattle area, said WSU butterfly expert David James.

Warm sunny summers for breeding and a lower number of predators such as birds and wasps probably boosted their population, he said.

With those conditions working in the butterfly’s favor, “they do very well in urban areas, which they navigate with ease using their five-inch wingspan and they can usually find all the flowers and host plants they need in the suburbs,” said James.

Numerous yellow butterflies on flowers.
Swallowtails gather to feed on common milkweed July 23 on Kamiak Butte near Pullman. (Photo by Robert Hubner, WSU Photo Services)

Unlike the migratory monarch, the tiger swallowtail remains at home base, traveling within a five-mile radius.

“It is a very active butterfly that never seems to rest except when feeding on backyard flowers,” he said, adding that the males are fluttering about looking for females, and the females are looking for host trees to lay their eggs.

The tiger swallowtail is a master illusionist, using its tail-like projection to fool birds into attacking the hind area of its body instead of its critical head. That’s why it’s not unusual to see otherwise perfectly healthy swallowtails missing tails snipped off by bird beaks, James explained.



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