February 7, 2007, Mary Jo Anderson spoke to the WBA membership about the trials and tribulations of raising silverspot caterpillars. Here is an update on the project.
OREGON ZOO RELEASES RARE SILVERSPOT CATERPILLARS INTO WILD
Zoo and conservation partners hope to increase Oregon silverspot population
PORTLAND, Ore. — For the first time, Oregon silverspot caterpillars raised in the Oregon Zoo’s butterfly conservation lab have been successfully released into the wild, marking a significant milestone in the effort to save this endangered Northwest butterfly.
“In the past, we have released pupae at the various sites, but this is the first time we’ve released Oregon silverspot caterpillars,” said Mary Jo Andersen, zoo butterfly keeper. “Within seconds of being placed on a western blue violet leaf, many caterpillars immediately started eating, despite the rain and wind!”
The release took place Thursday June 28 at a site south of Newport, Ore. The zoo hopes that releasing the large larvae instead of pupae will allow the butterflies to pupate and eclose on their own in a natural setting.
The zoo has been rearing endangered Oregon silverspot butterflies in its conservation lab for seven years in hopes of stabilizing the declining population. Each year, female silverspots are collected from Mount Hebo and induced to lay eggs at the zoo’s butterfly-breeding facility. Last fall, the zoo got more than 8,000 eggs from 32 female silverspot butterflies. These eggs hatched into more than 6,000 tiny larvae/caterpillars, which were kept in refrigerators over the winter.
This spring, the caterpillars were removed from their winter hibrination/diapause containers and have been fed thousands of blue violet leaves propagated by zoo horticulturists. Each caterpillar needs up to 200 leaves to grow and pupate.
“The zoo has an army of summer interns and volunteers who are feeding and cleaning the thousands of caterpillars!” says Andersen. “It is a massive undertaking at a critical time for this species’ survival.”
The Oregon silverspot butterfly is listed as threatened under the U.S. Endangered Species Act. It was once found in coastal grasslands from northern California to southern Washington, but has since disappeared from all but a handful of sites along the Oregon coast due to habitat loss and the disappearance of its host plant, the western blue violet.
“This conservation effort is serving as a model for rebuilding an ecosystem,” said Tony Vecchio, Oregon Zoo director. “Through the combined efforts of Seattle’s Woodland Park Zoo, the Nature Conservancy, and the U.S. Fish and Wildlife Service, we hope to stabilize the butterfly population and bring it back from the brink of extinction.”
During the preceding decade, monitoring at Cascade Head revealed a dramatic decline in the number of butterflies seen flying. In years prior to 1992, average numbers exceeded 1,000 adults, but in 1998, only 57 of the butterflies were found.
In 1999, in response to the dramatic decline in the butterfly population, the Oregon Zoo, Woodland Park Zoo, Nature Conservancy, Washington Department of Fish and Wildlife,
U.S. Fish and Wildlife Service and others took action to save the threatened species and its habitat.
Currently, the Nature Conservancy, working collaboratively with U.S. Forest Service, is restoring the native butterfly’s habitat through small, controlled burns. Scientists hope that by bringing back the western blue violet — which silverspot caterpillars depend on for food — the butterfly population can return to its historic numbers and natural habitat.
“Our cooperative conservation efforts are being seen more and more as part of the new zoo ethic,” said Andersen. “It’s becoming quite common for zoos to work outside their traditional captive programs to aid in the protection of species in their natural habitat.”
The zoo is also involved with conservation projects involving Taylor’s checkerspot butterflies and Mardon skipper butterflies.
According to Vecchio, butterfly populations throughout North America are in decline with 22 butterfly species listed as either endangered or threatened. To address this problem, the Oregon Zoo has supported the Association of Zoos and Aquariums’ Butterfly Conservation Initiative, which includes nearly 50 national zoos and aquariums. The initiative is designed to bring together government and non-government agencies to aid in the recovery of imperiled North American butterflies.
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