This post was sparked by our discussion in comments with reader JMC, who advocates replacing the Sutro Forest with Mission Blue habitat (disturbed grassland with lupines and other flowering plants).
Recently, a Mission Blue butterfly was spotted on Twin Peaks amid much jubilation. It seemed like a successful experiment in establishing an additional population of the endangered insect. (The main population is on San Bruno Mountain.) While one butterfly is certainly a lot better than no butterflies, it seems to us that the jubilation is premature. As we said in our response to the comments, we’re rooting for the Mission Blue, and admire the effort by the Parks and Recs staff and the volunteers who made this elaborate reintroduction. But we think it’s too early to celebrate.
This butterfly is the end result of extensive work and the input of 22 pregnant Mission Blues.
- It was a multi-year effort. First, lupine, the food plant, was planted (the caterpillars feed on three different kinds of lupine).
- Once that was established, 22 pregnant female butterflies were brought to Twin Peaks from San Bruno Mountain in April 2009.
- They were placed in net cages over lupine plants so they would lay their eggs there.
- According to the Draft Restoration plan, each female could lay “up to several hundred eggs.” This means 2-3000 eggs could have been laid. Maybe as many as 6,600…
Mission blue eggs hatch into caterpillars which eat the lupine, shedding their skins as they grow. The larger caterpillars are tended by native ant species, who protect them from predators while benefiting from “honeydew” – sugary caterpillar pee. When they’ve grown to their full size, they form their pupae near the base of the plants, or even on the soil beneath, and remain there for months. They hatch into butterflies in spring, sip nectar from a range of flowers, mate, and lay eggs on lupines.
With a life-cycle of about a year, April and May would be around the time for the hatching. Only a single butterfly was spotted. [Edited to Add: None were seen during the June 7th Butterfly Count, but it may have been too late in the year.]
Of course, spotting only one (male) butterfly didn’t mean he was alone. We hope there were more, with enough of each sex, so they found mates during their one-week lifespan. Otherwise, it’s going to be like that old joke: The easiest way to make a million dollars is to start with five million…
[Edited to Add (March 2011): We obtained a report from SF’s Parks and Recreation Department about the Mission Blue. Over nine surveys, they actually spotted 6 female and 11 male butterflies. The report extrapolates that the population could be 20-50 butterflies with the lower number more likely. The report recommends bringing in another 25 butterflies in 2011 to add genetic diversity. “the status of the population will remain tenuous until substantial population increases occur,” it notes.]
[Edited to Add (April 2012): Click here for an updated article about the Mission Blue Butterfly on Twin Peaks]
GARLON AND MISSION BLUES
If we have a win this year, it’s still not over. The fact that the 2010 batch succeeded (if it has) doesn’t mean that the next generation will make it. Though JMC believes Garlon used on Twin Peaks has “little to no effect“, one butterfly does not prove the point. And there’s no Garlon research on larvae; the insect research was on adult honey-bees.
The starter group of 22 Blues were caged over selected lupine plants, hopefully in a Garlon-free area. But will the butterflies make the same choice?
The butterflies may not be as vulnerable to Garlon, since they fly from flower to flower and only live a week or two anyway. But they may feed from nectar on Garlon sprayed flowers. We know it can cause birth defects in rats. We don’t know what it does in butterflies, because there haven’t been studies. Does it reduce the number of viable eggs? Does it decrease the number of healthy caterpillars hatched? We don’t know.
Even if hatched healthy, the caterpillars they live near or on the ground for months, and would be more vulnerable to toxins than the adult butterflies. Does the Garlon reduce the success rate of caterpillars? We don’t know that either.
We also don’t know about the impact of Garlon on the native ant species that “nurse” the caterpillars. Is Garlon favoring Argentine ants? And will Argentine ants behave the same way as native ant species? One student has observed them milking caterpillars of a different species of butterfly, so there’s hope. But they might also view the eggs and caterpillars as food.
And quite aside from the risks from Garlon, there are all the usual dangers: Weather conditions, predators (mainly birds) [ETA: rodents also prey on the larvae and pupae, apparently; and a parasitic wasp is also a problem], and just the normal variation in reproductive rates.
Even if the reintroduction is successful – as we hope it will be – we disagree with JMC on the value of destroying another flourishing eco-system in Sutro Cloud Forest. This region has other open spaces where lupine grows or could be grown, and Mission Blues reintroduced. That’s what diversity is about – having both the coastal scrub and the Sutro Cloud Forest.