Monarch butterfly populations have plummeted to a historic lowthis year, according to UC Davis professor Arthur Shapiro, who has been monitoring butterfly numbers regionally since 1972. Shapiro would normally have spotted up to 5,000 monarchs by late summer but reports seeing only 40 to date in California's Central Valley. He says disease, several years of drought, this year's wet winter and natural cyclical population patterns all may have played a role in the low numbers throughout the West. "There's no reason to think human activities have any role in this," Shapiro says, "but if you find them, you should leave them alone so you don't slow their recovery." Many schoolteachers collect the large orange butterflies with black-veined wings and white spots and their caterpillars for classroom illustrations of metamorphosis and the insect life cycle -- an exercise that might be good to skip this year.