Zoo releases hundreds of rare butterflies at coast

Conservationists transport Oregon silverspot caterpillars to sites along coastal range

The Oregon Zoo bid a fond farewell to hundreds of its tiniest residents recently.

Zoo conservation specialists and their partners released 1,304 Oregon silverspot larvae as part of an effort to save this beautiful and threatened Northwest species. The caterpillars were reared at the zoo and will complete their transformation into butterflies this summer along the Oregon coast.

Once common in coastal grasslands from Northern California up into British Columbia, the Oregon silverspot remains today in just a few isolated populations. Wildlife biologists are currently working to establish additional populations at Nestucca Bay and Saddle Mountain, where a rare and delicate flower — the early blue violet — still blooms in abundance.

Early blue violets are the main food source for the silverspot caterpillars as they mature into adult butterflies, and the Oregon coastal range is one of the few remaining areas where these flowers grow in quantities large enough to sustain a butterfly population. Elsewhere, they have been choked out by invasive weeds and forest succession.

“Oregon silverspots can only thrive in certain environments, and much of their former habitat has been lost,” said zoo conservation propagation specialist Julia Low. “But we can still give them a fighting chance at survival.”

Each summer, a small number of female silverspots are collected by field biologists and brought to the zoo to lay eggs. The eggs hatch into tiny caterpillars, which are kept safe during their winter dormancy. In the spring, they wake up to a leafy meal and grow quickly. When the time is right, the zoo and its conservation partners transport the caterpillars to field sites for release.

About 80 caterpillars stayed behind this year — a “rear guard” of sorts that will complete their transformation into adult butterflies at the zoo, then breed and lay eggs for next year’s release. In 2019, the Oregon Zoo became the first facility to successfully breed silverspots, Low said.

The zoo’s recovery efforts are conducted in partnership with the Oregon Parks and Recreation Department, the U.S. Fish and Wildlife Service and Seattle’s Woodland Park Zoo. The Oregon Zoo has released more than 36,000 Oregon silverspot butterflies since the program began in 2000.