Year 9 of Mission Blue Butterfly on Twin Peaks: Mixed Results

Mission Blue Butterfly - Public Domain Image

Mission Blue Butterfly – Public Domain Image

It’s now Year 9 of the the Mission Blue butterfly project on Twin Peaks, San Francisco. In 2008, SF Recreation and Parks Department (SFRPD) started trying an attempt to reintroduce the Mission Blue Butterfly to Twin Peaks, by planting lupine and transferring in breeding butterflies from their largest existing population on San Bruno Mountain. The results so far have been mixed:

  • The lupine needs continual care;
  • The butterflies are breeding on Twin Peaks;
  • Most years, imports of Mission Blue butterflies from San Bruno continue to be needed to boost the population and its genetic diversity.

In 2017, SFRPD observers spotted 30 butterflies that were actually born on Twin Peaks. They didn’t import any butterflies from San Bruno. But the lupine, the nursery plant of the butterfly, was badly hit by funguses and hungry voles.


The Mission Blue butterfly (Aricia icarioides missionensis) is a rare subspecies of the much more widespread Boisduval’s Blue (Aricia icarioides).  The species is not endangered, but the subspecies is found only from San Bruno to Marin and is federally-listed as endangered. The largest population is on San Bruno Mountain.

Lupine is the nursery plant of the Mission Blue. It’s the only plant on which it’s known to lay its eggs and which the caterpillars eat. 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.

Ant tending Mission Blue butterfly larva. NPS image

Ant tending Mission Blue butterfly larva. NPS image

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 (in diapause). They hatch into butterflies in spring, sip nectar from a range of flowers (including the “invasive” non-native Italian thistle: Carduus pycnocephalus), mate, and lay eggs on lupines.

These butterflies have only one generation a year and an 8-10 week flight season, becoming visible in April and May. The males live an average of 7 days, and females for 8 days. The males usually hatch before the females do, so they are ready to mate when the females appear.


Mission Blue butterflies used to inhabit Twin Peaks in San Francisco, but in 1998 a wet winter encouraged a fungal pathogen that destroyed most of the lupine plants – and the Mission Blue butterfly will not breed on anything else. The population, already small, fell until it was essentially gone. Eventually, SFRPD decided to attempt a reintroduction by planting lupine and then bringing butterflies from San Bruno Mountain.

The first batch, 22 females, was brought over in 2009. Optimistically, they hoped that this would be sufficient. But in 2010, only 17 butterflies were spotted, and imports resumed in 2011 – and in 2012, 2013, 2015, and 2016. In the graph below (covering the years 2009-2017) the dark bars show the “native-born” butterflies on Twin Peaks – i.e. ones that were spotted before transfers from San Bruno, or in years when there were no transfers. The light bars show the butterflies imported to Twin Peaks.  In 2017,  they’ve spotted 30 native-born butterflies.


[We’ve been reporting on this project for years; our most recent report is here: Mission Blue Butterfly 2016 Update: Imports from San Bruno Continue]

A report from SFRPD and its consultants on the year 2016 was issued in April 2017. It said they would not import any in 2017. But if the numbers fall in 2018, they’ll restart. The US Fish and Wildlife permit to transfer up to 20 male and 40 female butterflies each year is valid through 2020. They imported 44 butterflies from San Bruno in 2016: 15 males and 29 females.  You can read the report here: TwinPeaksProgressReportApr2017

According to that report, they were going to stop counting adult butterflies.  They planned instead to count the eggs, and calculate backward to figure how many females were implied by the number of eggs.  However, in 2017 they did in fact count butterflies, and found 15 males and 15 females in April and May.

This is the most of any year since 2009 – and definitely the most females. (However, there’s a bias because for each season we only use observations from before the transfers from San Bruno. But the transfers, too, must be made during the flight season. So in years with transfers, the local observation time is lessened and is biased to males, which emerge earlier than females.)  Despite the improvement, it suggests the population is still small enough that it cannot be considered stable or self-sustaining.

(The graph below is similar to the purple one above, but breaks out the observations – and imports – by the sex of the butterflies. The darker bars show imports, the lighter bars indicate butterflies that were born on Twin Peaks.)


It’s been a brutal year for lupine  in 2017 owing to the wet winter. There’s been a population explosion of voles, which have eaten some of the largest plants down to the ground. (A fungus has killed many of the lupine plants. Field notes describe it as anthracnose, but we’re not sure if a positive identification was made.)

In any case, this is never going to be a self-sustaining situation. They will need to keep gardening for lupine, because lupine is a plant of disturbed areas and Twin peaks isn’t disturbed.  As the report points out “unmanaged habitat degrades quickly.”

And while they can set up Mission Blue butterfly populations that are temporarily self-sustaining, in the long term they will still need to boost the population with imports.


We have a suggestion. Since lupine will have to be gardened anyway, why not grow it in containers? This should offer some protection from both voles and funguses, and provide the opportunity to optimize the soil conditions including drainage for the plant. SFRPD plants three species of lupine at Twin Peaks: Lupinus albifrons, lupinus varicolor, and lupinus formosus.

The favorite of the Mission Blue caterpillar is apparently Lupinus albifrons, or silver lupine; according to the April 2017 report, that was the only one the caterpillars were eating. And that one grows nicely in containers. The photograph below is from the website of specialist plant supplier Annie’s Annuals, specializing in rare and unusual annual & perennial plants, including cottage garden heirlooms & hard to find California native wildflowers.”

As a bonus, since container-grown plants won’t face competition from other wild plants, SFRPD can stop using toxic herbicides on Twin peaks. In 2016, they used toxic herbicides 25 times on Twin Peaks – behind only the much-larger McLaren Park (27 times) and Bayview Hill (34 times).  This included 7 applications of Garlon, possibly the most toxic herbicide the city permits.

It’s unknown whether these herbicides impact the reproductive success of the butterflies, either directly or via their ant tenders. In any case, organic lupines might be a healthier option.


These are the main issues with Garlon, in brief:

  • Garlon “causes severe birth defects in rats at relatively low levels of exposure.” Baby rats were born with brains outside their skulls, or no eyelids. Exposed adult females rats also had more failed pregnancies.
  •   Rat and dog studies showed damage to the kidneys, the liver, and the blood.
  •   About 1-2% of Garlon falling on human skin is absorbed within a day. For rodents, its absorbed twelve times as fast. It’s unclear what happens to predators such as hawks that eat the affected rodents.
  • Dogs  may be particularly vulnerable; their kidneys may not be able to handle Garlon as well as rats or humans.  Dow Chemical objected when the Environmental Protection agency noted decreased red-dye excretion as an adverse effect, so now it’s just listed as an “effect.”
  •  It very probably alters soil biology. “Garlon 4 can inhibit growth in the mycorrhizal fungi…” ( soil funguses that help plant nutrition.)
  •  It’s particularly dangerous to aquatic creatures: fish (particularly salmon); invertebrates; and aquatic plants.
  •  Garlon can persist in dead vegetation for up to two years.

If SFRPD grew the lupine in containers, it wouldn’t need to worry about the oxalis or use Garlon. At least on Twin Peaks.


We are often asked how much the Mission Blue project is costing the tax payer, so we tried to find out. This project is funded by the city, and with a three-year grant from US Fish and Wildlife Services for “habitat management” that just ended.  Data for 2008-2017 indicate the SF Rec and Parks Commission spent around $82,000. We looked at Professional Services payments to Coast Ridge Ecology, to Creekside Center for Earth Sciences, and to Liam O’Brien. There’s another consultant involved, Golden Hour Restoration Institute, but we think they were paid directly from the US FWS grant.

This of course excludes the salaries/ time of the SFRPD staff. Natural Resource Department staff are involved at every stage, from lupine planting to butterfly counting. It also excludes the cost of laying down pesticides on Twin Peaks 25 times annually.


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