The Mission Blue Butterfly

Male - Marin Headlands

Like so many other urban animals, the Mission Blue Butterfly (Plebejus icarioides missionensis) is one that is gravely imperiled.  This small blue lives in tiny fragments of habitat alongside multi-million dollar development in and around the San Francisco Bay.  A century ago this butterfly was already starting to decline, with hundreds of acres of beautiful seaside morphing into sprawl.  Today the coastal sage scrub has nearly vanished and what little remains is infested with invasive plants and animals.

The Mission Blue was one of the first animals listed on the Endangered Species Act, acchieving offical protection in 1976.  Efforts over the last few years have focused on restoring the habitat and the blue within it – with limited success.  Before 2009 the last blue seen within the city limits was on Twin Peaks in 1997 (and possibly the 1970’s before that).  Today the SF Recreation and Parks Department along with Bay Nature has somewhat re-established the Mission Blue on Twin Peaks from healthier populations in the Marin Headlands and San Bruno Mountain (the only other locations the butterfly is known from).  I believe last year they had around 30 individuals flying on Twin Peaks.  This year the numbers are down, but on Friday I found three females ovipositing on lupine – while these females were probably transplanted a few weeks ago, it is hope for the future.  Unfortunately the only males I saw were up in the Marin Headlands – and hopefully males were seen on Twin Peaks this year (pending 2011 data).

Not surprisingly, it turns out that reintroducing a species is a complicated game.  The Mission Blue utilizes three host lupine species, Lupinus albifrons, formosus and variicolor. Yet maintaining these native species amongst the invasives requires radical measures including heavily applications of herbicides (against fennel, pampas grass and french broom – but including 136 other invasive plants (Marin Flora)).  It is unknown what effect the herbicides have on developing larvae (only 17% success from egg to caterpillar) or what it does to native ant populations that tend the caterpillars of the blue.  Without native ants the caterpillars are much more likely to be predated, but even native ants are falling to the invading hoards of Argentine ants.  And yet another key player is a newly found fungus that is killing lupine plants – devastating butterfly numbers in 2010.

If you compare this subspecies to other members within the icarioides complex there is a striking difference in abundance.  Plebejus i. moroensis from the central coast is an incredibly abundant butterfly within good habitat.  It is highly restricted, but not facing nearly the difficulties the Mission Blue is.  I hold out hope for one of our last San Francisco blues – if the invasive species can be controlled – it won’t go the way of the Xerces.

Relocated female - Twin Peaks SF

(more images below)

Same female - Twin Peaks SF

Aberrant male - Marin Headlands

Deformed male - Marin Headlands

This deformed male was found in the middle of a trail and could barely fly (see the curled right forewing).  I attempted to move it off the trail when it crawled on my hand.  Otherwise, I do not recommend ever handling endangered species!

And most importantly, special thanks to Liam O’Brien from Nature in the City for guiding me to these localities!