In the 1960s, Stanford Biology Professor Paul Ehrlich began a long-term study of the Bay checkerspot butterfly in what is now Carol Boggs, professor (teaching) of biology at Stanford. 

But by 1998, the Bay checkerspot had gone extinct on Jasper Ridge. Today it is federally classified as “threatened” throughout its range. In 2005, the Woods Institute awarded Boggs, Ehrlich, and their colleagues an Environmental Venture Projects (EVP) grant to determine why the extinction had occurred and whether the butterfly could be reintroduced to Jasper Ridge. 

Native to the San Francisco Bay Area, the Bay checkerspot’s lifecycle is specifically suited to its natural habitat. Each spring, it lays its eggs in clusters on a native plant called the dotseed plantain, or Plantago erecta. When the eggs hatch, caterpillars emerge and develop until they are big enough to enter diapause, a hibernation-like state that usually occurs before the onset of the summer dry season. “The trick for the butterfly is to get there before the plant dries out from underneath it,” says Boggs. She points out that 90 percent of checkerspot mortality is due to the inability of caterpillars to reach diapause before the spring rains stop. 

Climate is crucial, Boggs adds. “The butterflies really like the Goldilocks solution,” she explains. Too much rain causes the caterpillars to eat too slowly because of lack of sunlight. Too little rain causes the plantains to dry up fast. In either scenario, the caterpillars are unable to consume enough plant material to enter diapause. The likelihood of an extremely wet or an extremely dry year is much greater today than in the past. According to Ehrlich and his colleagues, this increasing variability in rainfall since 1970 is one of a combination of factors that led to the decline in checkerspot populations. 

The butterfly’s habitat also has been limited by competition from invasive grasses. Today, dotseed plantains are only found in serpentine soil, which has an altered magnesium-to-calcium ratio that’s not conducive to most non-native grass species. In addition, human encroachment has paved over some serpentine soils, further limiting habitat for the butterfly. 

Restoration hurdles 

Reintroducing a threatened species is challenging enough from an ecological viewpoint, but the legal aspects of reintroduction have raised a whole new set of problems for the researchers. Buzz Thompson, a professor of law at Stanford and co-director of the Woods Institute, served as the research team’s legal expert and discovered a number of regulatory barriers to a full reintroduction. For example, to conduct experiments with a species listed as threatened by federal and state governments, permits must be acquired from the U.S. Fish and Wildlife Service and the California Department of Fish and Game. But according to Boggs, state Fish and Game officials initially would not allow the checkerspot experiment to proceed unless researchers were able to guarantee that the butterfly population would persist—an extraordinarily difficult condition to meet. And Thompson points out that if wetlands are affected, permission to conduct the experiment also must be secured from the U.S. Army Corps of Engineers. 

Because of these and other legal and scientific hurdles, it is unlikely that reintroduction will begin any time soon. However, the EVP research team has made important strides in understanding the complex environmental challenges facing the checkerspot. With the help of two team members from the Stanford History Department, Professor Richard White and graduate student Jon Christensen, the researchers discovered that the decline in checkerspot populations coincided with the removal of cattle from the butterfly’s habitat. One possible explanation is that the cattle consumed non-native grasses that competed with the butterfly’s plantains. In another finding, biology graduate student Tim Bonebrake, working with Boggs and other team members, showed that the mineral content in serpentine soils may not be as important to the plantain’s success as soil drainage.            

For Boggs, the longevity of the reintroduction project is a primary concern. The next step is to acquire external funds to create an artificial serpentine habitat for experimentation–a multi-year project that, once completed, could keep graduate students busy for years to come.          

“The Bay checkerspot reintroduction effort is exactly the type of project that the Woods Institute wants to encourage,” adds Thompson. He points out that EVP grants are, by definition, interdisciplinary, and the butterfly project has brought together a unique team of researchers from the sciences, humanities, and law. “Biologists and lawyers have sometimes worked together in the past, but we don’t know of any situation where historians have been brought in to this type of ecological reintroduction program,” Thompson says. “More important is the possibility of real change resulting from an EVP project like this one.”       

Nate Sulat was a writer-intern at the Woods Institute for the Environment in summer 2008. 

Professor Carol Boggs discusses habitat restoration for the endangered Bay checkerspot butterfly. (20:31)