Twin Peaks and the Mission Blue Butterfly: Why it’s Still Uncertain


Last year, journalists were celebrating the return of the Mission Blue butterfly to Twin Peaks. From the SF Chronicle of 7 May 2010: “Everyone comes back to San Francisco, including, on a bright morning on Twin Peaks, the endangered mission blue butterfly.” It went on to say, “Last seen within city limits 30 years ago, the iridescent blue butterfly was spotted Thursday morning flitting about a Twin Peaks hillside…”

Leaving aside the issue of when the Mission Blue was last seen at Twin Peaks (1997 actually and one each in 2001 and 2004),  we wondered whether the single butterfly proved anything much.

The butterfly used to live on Twin Peaks, but it’s not clear how stable the population was. By 1997, only ten butterflies were seen. After that, hardly any were until the recent reintroduction attempt. Some blame the warm wet El Nino conditions of 1998 for a fungus that nearly wiped out the silver lupine, a key host plant for its caterpillars.


This “return” was the result of a complicated reintroduction, starting in 2008 with establishing patches of lupine, the host plant on which this butterfly lays its eggs. In spring 2009, the reintroduction team (which was led by SF Rec & Parks — SF RPD) brought in 22 pregnant females, and caged them over suitable lupine plants to lay their eggs.

We recently got SF RPD’s October 2010 report on the Mission Blue reintroduction. The team had counted 147 eggs laid in 2009. Over the following months, through end-May, they actually saw a total of 17 butterflies: 6 female, 11 male. Extrapolating, they thought there could be perhaps 20 butterflies this year; the number was unlikely to be as many as 50. [ETA June 2011: Before releasing the 60 butterflies in April 2011, they did check to see if any butterflies descended from the previous release were around. They spotted 2 males. ETA Feb 2012: We asked SFRPD for their observations. They actually spotted 7 butterflies pre-release, 5 males and 2 females.]

Is that success? The report considered it so, mainly because it demonstrated that the butterfly could go from egg to adult on Twin Peaks.


Mission Blues can’t reproduce without lupine, the only plants their caterpillars will eat. This plant (actually three varieties of it) grows best in disturbed areas. Once the area settles down, natural succession converts it to chaparral, or other invasive plants take over. Patches of lupine are generally on the move.

The Natural Areas Program (SF NAP, the part of SF RPD that’s responsible for Twin Peaks) is maintaining a lupine-friendly habitat by removing shrubs, including the native coyote-brush. The implication, though, is that this intervention will be permanent and ongoing. They will always need to garden for lupine.

While the lupine is critically important to the caterpillars of the Mission Blue, the adults need nectar sources. The butterflies are short-lived (7 days on average for males, 8 days for females) and don’t fly far. Fortunately they aren’t as picky as their larvae, and one of their key nectar sources is an invasive non-native Italian thistle: Carduus pycnocephalus. This grows widely on Twin Peaks, and SF NAP is not trying to remove it for now, until they can plant enough native nectar sources.

In attempting to maintain this lupine habitat for the Mission Blue, SF NAP has been using toxic herbicides: Garlon (triclopyr) and Roundup or Aquamaster (glyphosate). Both have been used all over Twin Peaks.  (Our article about the effects of Garlon is here.)


Notices: Mission Blue Habitat, Garlon spraying, and No Smoking

We have to wonder whether the success rate (egg to butterfly) will be similar to the 2009 batch — around 14% of the eggs becoming butterflies.   Though SF Rec and Park believe that Garlon isn’t harmful to insects, there really isn’t any way to tell. The studies on triclopyr relate to adult honeybees. Whether the chemicals — both the triclopyr and the “inert” chemicals used with it — will be non-toxic to caterpillars, we don’t know.

[ETA, March 2012: A study of the effects of Triclopyr and other herbicides on Behr’s Metalmark butterflies indicated adult butterfly emergence fell by 24-36%. Is it the same for Mission Blues? We don’t know.]

Mission Blue caterpillars hatch from eggs laid on lupine leaves (new leaves are preferred). They eat the leaves, then climb down into the dead leaves or ground beneath the lupine plants, and go into a sort of hibernation, called “diapause.” After emerging from diapause, they continue feeding, then pupate and emerge as butterflies between March and June. This life-cycle takes a year and brings them into contact with the soil. If that’s been contaminated with Garlon (which can remain in dead vegetation for up to two years) it could poison the caterpillars and reduce the chances of success.

There’s an additional effect possible: Garlon’s unknown impact on ants.  The main threats to Mission Blue larvae are parasites (like wasps and flies that lay eggs on the caterpillar) and predators. Ants tend the caterpillars, which emit honeydew, a sugary pee that ants use for food. The caterpillars benefit because the ants defend them. At least, the native ants do. But Argentine ants are moving into many habitats, and no one knows whether they will tend the caterpillars or eat them instead. One study in Marin suggests that Argentine ants tend the caterpillars of a similar species of butterfly, the Acmon Blue. But another from Florida suggests that Argentine ants use the honeydew but run off when the caterpillar is threatened.

What we don’t know is whether the use of Garlon favors Argentine ants by having a negative effect on ant pupae — thus giving the more competitive ants a clearer field. [ETA: Just read an interesting post on the blog Golden Gate Park: Views from the Thicket about an ant study conducted in 2008 conducted in August-Sept 2006, published in 2008. Argentine ants were present but not invading the parks. Hope it’s still that way. The study is here (as a PDF): argentine ants san francisco research – Clark Fisher- LeBuhn]


We find the numbers interesting, and perhaps indicating less success than the optimistic journalistic stories.  The report suggested that the imported females may have already laid half their eggs back home on San Bruno Mountain, so the 20 or so butterflies came from only the second half of the eggs. (So maybe if they’d laid them all at Twin Peaks, and the same ratio had succeeded, there’d have been say 40 butterflies, with maybe 12-15 females. Down from 22.)


The introduced Mission Blues were caged over selected lupine plants to lay their eggs; their descendents selected their own sites. A survey in February and May 2010 found 42 eggs. The observers saw more than that, but the sampling method they used didn’t permit counting them. Still, it’s not an encouraging number. Unless they’ve missed 70% of the eggs, there are fewer eggs in 2010 than in 2009. At 42 eggs, they’ve got 7 eggs per observed female, about the same ratio as in 2009 (which was 147 eggs from 22 females).

This population is clearly dwindling.


At this size, the population isn’t viable. Here’s why:

1. The dating game. These insects don’t live long (about a week), and they emerge between March and June. The males usually hatch earlier than the females, which is a good idea when there are lots; it means they’re ready to mate the females as soon as they hatch. With only a few butterflies, though, the males could die before the females arrive. Some females might not find mates at all, and thus not reproduce.

2. Inbreeding. Having such a tiny number increases the chances of the mating pair being siblings. They could lower their breeding success.

3. Bad luck. Anything could upset the numbers still further — birds, rodents, bad weather — and wipe out the colony. The small number means there’s no buffer.

4. The fungus remains. The fungus blamed for killing the lupine in 1998 remains in the soil of Twin Peaks, according to a Fish and Wildlife report. This could mean adverse weather could again kill off the lupine — and the butterflies.


The plan now is to move 25 more female butterflies from San Bruno Mountain (assuming US Fish and Wildlife Service gives the permits).

[Edited to Add (24 April 2011):  According to the SF Chronicle, they are relocating “dozens” of butterflies now. There’s a photograph at this link.]

[Edited to Add (2 June 2011): We asked the Parks Department. They got permission to relocate 60 butterflies — 40 female and 20 male; and did so on April 22, 2011. Not sure if they released all of them at the same time or not. ETA (2 July 2011) We found this blog post on Liam O’Brien’s new website, describing the process.]

It may be a long haul, establishing the Mission Blue. The Recovery Action Plan Document (from SF RPD) indicates that in the UK and US successful reintroductions took an average of 11 attempts — and 15 years.

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9 Responses to Twin Peaks and the Mission Blue Butterfly: Why it’s Still Uncertain

  1. Charlie says:

    Why is ‘gardening’ or close human management of wildlands continually being described in such negative terms here?

    Before the Spanish came to California, a LOT of the land was being ‘gardened’ – it was being intensely managed by different Native American groups in a style of permaculture using hundreds of different plants native to California (they didn’t have access to other plants, to be fair). Obviously this is a generalization – some Native American groups destroyed and heavily altered habitat, like any other human group. BUT… the pre-colonization landscapes of California were not a wilderness untouched by humans, but a complex ecosystem in which humans played the central role (much like beavers play in riparian areas of the Northeast). Some (see the book Tending the Wild) actually described parts of California as a virtual Eden where hundreds of wildflower species produced edible seed; oaks produced millions of pounds of acorns; salmon filled the streams; and elk and deer ate the parts of these plants the humans couldn’t (and in turn were eaten by humans and grizzlies).

    I think there are valid points about restoration being made in defense of Sutro but what is being missed is the native plants, themselves, are also very intimately connected to humans. Or, they are supposed to be. I honestly think this is part of why invasive plants are such a problem here. What happens when you leave a field of wheat fallow for 200 years?

    [Webmaster: Possibly you’re right. Then the question becomes, why are we trying to restore a farm that nobody will harvest? It isn’t “natural” in the usual sense of the word, it’s agricultural. It had a meaning when those who cultivated it built their lives on it; but those people are long gone. Now we have an artificial construct that must be maintained with herbicides because the measures the people of the past used — fire and grazing — aren’t appropriate inside a city (if you check the map, Twin Peaks is surrounded by housing, the reservoir, and Sutro Tower).]

    Humans have been in CA for at least 15,000 years – since the wet times at the end of the ice age. Many argue protection of native plants for their inherent ecosystem value and I don’t begrudge that. But I don’t hear anyone arguing protection of CA native plants as a potentially vast genetic resource for potential sustainable food and building material production.

    [Webmaster: Perhaps because no one wants to eat acorn flour or live in reed houses? Even those who have that past in their heritage don’t want that life-style any more. And some of those plants aren’t even edible now in the US: consider amaranth. It’s still eaten in other parts of the world, but here it gets too much nitrogen.]

    So you have to garden Twin Peaks? Let’s figure out some of the old methods that were used for 15,000 peaks and garden the place! People fight over tiny garden plots – let’s get people learning the old ways and gardening Twin Peaks the way it evolved with! I’ll bet the butterfly does great – or else it would be dead by now.

    [Webmaster: I suspect the problem may be that populations of the Mission Blue are inherently mobile, like the lupine they oviposit on. A USFWS study says, “each colony is dynamic and relatively short-lived…”
    They’re doing okay on San Bruno mountain, and new populations were discovered, with the next largest being near Skyline College.]

    If people were more connected to the land in that way, we could control the invasives – without herbicides.

    [Webmaster: We actually don’t know what was happening with Twin Peaks before ranching started there. It may have been grassland grazed by deer, or it may have been some kind of chaparral, or it may have swung between those two states.]

    On a side note, what’s with ” natural succession converts it to chaparral, or other invasive plants take over”. CHAPARRAL ISN’T INVASIVE!

    [Webmaster: okay, clarification in order. “Invasive” is a matter of context. If the plant’s growing where you want it to grow, then it’s “easy to grow.” If it moves in where you don’t want it to grow, it’s “invasive.” The people trying to preserve the grasslands *do* find some native chaparral plants like coyote bush invasive. Left to itself, chaparral will take over grassland. I’ll edit in some links later, I need to dig them up.

    ETA: Okay, here is the reference; it’s to the USDA website, and talks of succession from grassland to scrub to woodland. ]

    Come on, be fair… I know people are trying to shoo it out of some grassland areas, but it isn’t an invasive ecosystem, seeing as how it is shrinking in area each year.

    [Webmaster: It can actually be invasive in one context, and invaded in another. I read a study some time back that suggested that without human intervention in some coastal areas, oaks would “invade” chaparral, and eventually convert the area to oak woodlands. The real question is, why is the area of chaparral shrinking? Because it’s being replaced by agriculture (western-style)? Or being built on? I guess the bottom line is, ecosystems aren’t static. They change from year to year, from decade to decade. A fire might burn out chaparral, and leave grasslands for a few years until the chaparral comes back. Oak seedlings might take hold and convert parts of it into a forest. A fire or a bug might destroy the oak forest, and then grasslands or chaparral might recur. What’s happening now is that we try to nail these areas down. What I have a problem with is the illusion that it isn’t a garden, it’s a “natural” landscape. Oh, and herbicides.]

  2. celestial elf says:

    Great Post 😀
    thought you might like my machinima film the butterfly’s tale~

    Bright Blessings
    elf ~

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