Oregon Silverspot

Once found in coastal headlands from northern California to southern Washington, the Oregon silverspot butterfly (Speyeria zerene hippolyta) has disappeared from all but a handful of sites along the Oregon coast. The Oregon silverspot population at Cascade Head declined from 1,392 butterflies in 1989 to 57 in 1998. Development, pesticides, fire management, introduced plant species, grazing and off-road vehicles are all reasons for this butterfly’s decline. Since the first year of the program in 1999, nearly 500 larvae and pupae have been released at the Cascade Head and Rock Creek sites.

Oregon Silverspot Fast Facts

• Federally listed as threatened.
• Lab-rearing project at the zoo started in 1999.
• One female can lay hundreds of eggs.
• Caterpillars eat their own eggshell after hatching and immediately go into diapause (hibernation) from • October to May.
• Each silverspot caterpillar must be fed about 150 violet leaves before it becomes a butterfly.
• Average wingspan for adult butterflies is a little over an inch.

Silverspot Butterflies by the Numbers

Butterflies are collected from Mt. Hebo on the Oregon coast. They are fed a sugar mixture with egg white and water, and housed in paper bags with simulated leaf litter and temperatures above 85 degrees to encourage laying eggs. Eggs are collected and hatch after 10 to 15 days of incubation. The caterpillars are overwintered (put into diapause) in refrigerators. After they wake, the larvae are raised in jars and fed their host plant, Viola adunca. In 5 to 10 weeks, they grow from 1 to 35 millimeters. When they pupate, the chrysalids are taken to the coast where they emerge as butterflies.

Between 1999 and 2002, 200 pupae were returned to Cascade Head, and at least 112 butterflies emerged as adults.