Oregon silverspot butterflies get new places to grow

ASTORIA, Ore. – To release an Oregon silverspot butterfly caterpillar, biologist Anne Walker takes it out of a little Tupperware container and sets it gently on its preferred food, the spade-shaped leaves of the early blue violet.

It’s not as precarious as it sounds.

“They’re very adapted to their environment,” said Walker, a biologist with the U.S. Fish and Wildlife Service and a silverspot expert. “They hide.”

She’s seen released caterpillars dive down and seemingly disappear in moments. Somewhere down there, she knows, they are starting to munch on the first of the roughly 200 violet leaves they will each need to eat to survive to adulthood.

This is the end point of a process called “augmentation” – an ongoing effort to reintroduce the threatened silverspot butterfly by releasing caterpillars at specific sites across the state.

The U.S. Fish and Wildlife Service recently announced it will release hundreds of caterpillars at two new sites this summer and next: the Nestucca Bay National Wildlife Refuge in southern Tillamook County and the Saddle Mountain area in central Clatsop County.

The small reddish-orange butterflies with their distinctive silver spots were once found on coastal grasslands from Northern California to southern Washington, but development, changes to the forest and invasive weeds and grasses reduced the silverspots’ preferred habitat.

The decline is linked primarily to a lack of early blue violets, normally the only plant on which the Oregon silverspot can successfully feed and develop as larva, according to Fish and Wildlife.

These plants are crucial throughout a silverspot’s life cycle. Their presence stimulates the female butterflies to lay eggs in the first place. Later, young caterpillars feast on the leaves.

By 1980, the butterflies had vanished from at least 11 different localities. That same year, U.S. Fish and Wildlife Service listed the Oregon silverspot as a threatened species.

No one has ever documented a silverspot at the Nestucca Bay site, but this area is within the butterfly’s historical range, according to Fish and Wildlife. Why silverspots abandoned Saddle Mountain is mystery. The violets are still there, and thriving. The butterflies are not. They haven’t been seen there since the 1970s.

Nestucca will be the first of the two sites to get this new influx of caterpillars. Next summer, it will be Saddle Mountain’s turn. If these sites are successful, as biologists expect they will be, they will bring the overall population that much closer to recovery. Currently, silverspots are established at five sites; the ultimate recovery goal is 10 self-sustaining populations.

The caterpillars that biologists, such as Walker, will release this summer come from labs at Seattle’s Woodland Park Zoo and Portland’s Oregon Zoo.

Scientists collect female butterflies from the large wild population at Mount Hebo in Tillamook County’s Siuslaw National Forest and bring them to labs at the zoos. Here technicians coax the females into laying eggs. When larvae hatch from these eggs, they are so small you could put them next to a penny and they wouldn’t even be as long as Abraham Lincoln’s beard, Walker said. By the time they are released, however, the caterpillars are about an inch long.

Adapted to the environment, biologists are optimistic that caterpillars at Saddle Mountain and Nestucca will succeed, but they also know not all the caterpillars will live long enough to become adult butterflies.

“We don’t expect them all to survive,” Walker said. But, she added, “Probably one of their functions within the ecosystem is to be food for other things.”

Biologists expect to release approximately 3,000 caterpillars this summer; most will go to the Nestucca restoration site. Some will seed established sites and the rest will go back to areas where their mothers were collected.