Rare butterfly caterpillars are back on the slopes of Saddle Mountain for the first time since they completely disappeared from the area years before.

Government and private partners released 500 Oregon silverspot caterpillars on the mountain’s rocky meadow slopes recently as part of an ongoing effort to rebuild the threatened butterfly’s population at key sites. 

“It was a culmination of so much work and it was almost a celebration,” said Trevor Taylor, manager for the reintroduction project at the Oregon Parks and Recreation Department.

Last year, teams reintroduced caterpillars at the Nestucca Bay National Wildlife Refuge in southern Tillamook County with plans to release caterpillars at Saddle Mountain this year — a site Taylor describes as “prime real estate” for the red-orange butterflies marked with distinctive silver spots.

Elsewhere, the small butterfly’s decline has been linked to a decline in habitat but its disappearance from Saddle Mountain is more mysterious. There are several theories for the decline: past chemical spraying practices on surrounding timberland may have impacted the butterflies, or perhaps the butterflies were unable to weather especially rough winters. People who searched for silverspots on the mountain in the 1970s saw them; when people went looking again in the early 2000s, they were gone.

“We don’t know when the silverspots disappeared, we don’t know why they disappeared,” said Mike Patterson, a contractor for the U.S. Fish and Wildlife Service on the reintroduction project. “We can only speculate about why they disappeared and that’s speculation — there’s no way to prove it.” 

Saddle Mountain remains one of the few sites where the Oregon silverspot’s main source of food — another rare organism, the early blue violet — blooms in abundance. Other wildflowers also flourish there. The variety of blooms make the mountain a popular destination for hikers. For the butterflies, these flowers will provide additional sources of nectar, Taylor said.

Over the summer, many of the silverspots will die. Some will be eaten before they pupate, others will be eaten while they pupate or when they emerge as butterflies.

At the Nestucca site, Patterson could account for only 9 percent of the nearly 1,000 caterpillars released along his survey route. It was a number that concerned others involved, but not Patterson.

“Being able to account for only 9 percent doesn’t mean only 9 percent became butterflies,” he said. 

And he feels confident about the caterpillars’ success on Saddle Mountain.

“My guess is we’ll see butterflies,” he said. “The habitat is certainly ripe for them up there.”

Of the 500 caterpillars now chomping away at plants on Saddle Mountain, 280 larvae came from the Oregon Zoo’s butterfly conservation program, which raises as many as 10,000 Oregon silverspot and Taylor’s checkerspots in its lab at any given time to supplement wild populations. Larvae also come from labs at Seattle’s Woodland Park Zoo, the children of wild female silverspots collected from Mount Hebo in the Siuslaw National Forest in Tillamook County.

“Numbers are dictated year to year by (the Fish and Wildlife Service) but it is highly likely we will continue to operate at or near capacity over the next several seasons at least,” said Travis Koons, who oversees the Oregon Zoo’s butterfly conservation program. “We will continue to release high numbers of larvae at the various sites.”

The silverspot caterpillars were placed on early blue violets in three different areas on Saddle Mountain. Over the next few weeks and throughout the summer, Patterson and others will check different survey points, counting any adults they see. Though Patterson is confident this first reintroduction will find some degree of success, he said, “At the same, it’s not a one-time quick fix kind of deal. This is just the first of probably quite a few efforts to go up there and release more caterpillars.”

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