Return of the Checkerspot
March 2, 2018
The text came at 8:11 am. A week of late winter storms in Northern California had put the mission in jeopardy, but we had a window of clear weather. By 9:00, a squad of Presidio Trust naturalists and interns were rolling southbound in a van.
Behind the wheel, Jon Young, a Wildlife Ecologist with the Trust, announced that we were picking up Liam en route — Liam O’Brien, the go-to lepidopterist in the San Francisco Bay area. The mission sounded simple enough. Collect 200 caterpillars, and redistribute them in San Francisco’s Presidio.
The biologist E.O. Wilson called our destination, San Bruno Mountain, one of eighteen biodiversity hotspots on the planet most in need of preservation. To me, the phrase “biodiversity hotspot” conjures pictures of dense jungles and exotic orchids, raucous birds and buzzing insects, and maybe some screaming monkeys. San Bruno mountain is nothing like that. It rises abruptly from the San Francisco peninsula’s flatlands, a green island surrounded by industrial parks, cemeteries and freeways. The coastal scrub environment seems uniform from a distance, but up close, there’s a dense mixture of plants, fungus, insect and bird species. And as the elevation changes, the mix of species shifts, revealing more diversity.
But we haven’t come for any of the endangered species on San Bruno Mountain. We’ve come for one of the most common butterflies in the American west, found in abundance from New Mexico to Alaska. We’ve come for the Variable Checkerspot.
This butterfly is everywhere, but it’s been missing in the Presidio since the 1970s. Why? Loss of habitat. Butterflies, and especially, their caterpillars, are conservative in their habits. Monarchs prefer milkweeds. In California, Variable Checkerspots are looking for bee plants — Scrophularia californica. That’s what local baby Variable Checkerspot caterpillars eat, period. Not daisies, not English ivy, not Cheesy Puffs. We’re gathering caterpillars from bee plants, and we’ll move them to other bee plants in the Presidio, where they’ll eat more bee plant, settle down to become pupae, and in a few weeks, emerge as adult butterflies.
A brutal wind is blowing straight off the Pacific on the mountaintop. As we pile out of the van, everyone starts pulling on gloves and caps. Liam’s fur trooper hat now seems like a wise move. The interns (Darryl, Caileen, Sierra, Emily) Bridgette Haggerty, a Presidio Trust Biological Science Technician, and I trail behind Jon and Liam. Liam stops every few yards to point out different species of lichen here, a rare manzanita in bloom there.
Once we’re out of the wind, Jon points out the bee plants. “We’re looking for patches of Scroph,” abbreviating the plant’s Latin name. He scans a bit and shows us a caterpillar curled up on a leaf. About as big as a gummy bear, the caterpillar looks like an undersized bottlebrush, covered in black bristles. A row of bright orange spikes line its back. “There are nine of those spikes, Zip,” says Liam, “you’ll want to get that right when you sketch them.”
Jon hands out yogurt containers and stuffs a paper towel in each one. “You can just brush the larvae into your cup. If you find one, you’ll probably find more nearby. Keep count of how many you collect.”
Soon, I’m focused on the search. Spot a bunch of bee plants, scan them slowly for caterpillars. When I see one, I kneel down and scoop it into my yogurt bucket, and mentally add to my total. Where I find one larvae, I’ll find a half dozen more. I move, I look, I scoop…58, 59, 60, 61, 62 larvae. A white cup full of bristly black caterpillars.
Jon calls out to everyone — “How many larvae do you have?”
60…52… Jon adds everyone’s haul, and comes up with 560 caterpillars. Way more than today’s target; time to pack it up. The clouds were gathering and the wind was still blasting at the summit. We get in the van and head back towards San Francisco. I’m thinking about the focus of the volunteer work I do in the Presidio — habitat restoration. I ask Liam: what role does the Checkerspot play in the local ecology?
“They’re food for everyone else. People talk about pollination, but that’s because it sounds nicer than ‘host for parasitic wasps.’” And Liam lays out the “80% of 20%” principle.
“When a butterfly lays its eggs, only 20% of those eggs will hatch. The other 80% get eaten. Of those caterpillars who hatch, another 80% will get eaten. So 20% of 20% of the eggs make it to the pupa, or chrysalis, stage, and only 20% will survive to hatch as adult butterflies. And only 20% of those butterflies live long enough to mate.”
The percentages aren’t exact, but the principle is clear — it takes 100s of eggs to ensure that each pair of mating butterflies is able to replace itself. It isn’t just butterflies; most life on earth takes this “long odds, big numbers” approach to survival. Frogs lay lots of eggs. Every dandelion head contains dozens of seeds. If you’ve ever squeezed the fungus called a puffball, you’ve seen spores by the thousands.
Mammals and birds have a different strategy. They have just a few offspring at a time, and invest a lot of care into shepherding them to adulthood. Fewer bets, but better odds.
We returned to spots in the Presidio to finish the relocation process. First El Polin, then Wherry Corridor, and finally, Presidio Hills. We spread out and reverse the process, gently picking caterpillars out of the yogurt cups, and placing them on the leaves of bee plants. After years of restoration in the Presidio, bee plants are plentiful and widespread, so reestablishing the Variable Checkerspot stands a good chance of success.
In April, David Harrelson, another Trust naturalist, began patrolling the areas where caterpillars have been deposited and counted adult checkerspots on the wing. The results are excellent. For example, in 2017, 87 butterflies were seen at El Polin, over a full season of surveying. This spring, David counted 68 Checkerspots at El Polin — in a single day. It means that the Checkerspots let loose in 2017 are thriving, and beating those “80% of 20%” odds. As David says, “there’s lots of mariposa love here.” After a 40 year absence in the city, it looks like Variable Checkerspots are making a strong comeback.
Wait, there’s more!
Prefer video to words? Get another perspective on the Presidio Checkerspot reintroduction.
Learn even more about Checkerspots
All art by the author. see more at instagram.com/bigstickcharcoal
