Species Spotlight – Dwarf Plantain and Bay Checkerspot Butterfly

Dwarf plantain by D in Orbit, flickr; Bay checkerspot butterfly by Mark Grzan

In this season of spectacular wildflower blooms, if you’re observant enough you may spot the small, unassuming dwarf plantain peeking out of the grass among its more showy wildflower cousins. Dwarf plantain, or dotseed plantago (Plantago erecta), is a small annual wildflower that plays a fascinating, critical role in the life cycle of the threatened Bay checkerspot butterfly (Euphydryas editha bayensis).

This humble native plant was once widespread throughout California, but in many areas it has been displaced by invasive, non-native plants. Today it persists mostly on poor soils where there’s little competition, especially on grasslands with serpentine soils, such as Coyote Ridge south of San Jose and Edgewood Park near Redwood City. It sprouts early in the winter rainy season, then rapidly grows, flowers, releases its seeds, and withers as soils dry out in April-May.

A Critical Partnership

Dwarf plantains play a dramatic role in the life of the Bay checkerspot butterfly, and the decline of the dwarf plantain is one of the factors contributing to the butterfly’s struggle to survive. The Bay checkerspot’s larvae use the dwarf plantain as a food source, so female Bay checkerspot butterflies seek out the plantains when they’re ready to lay their eggs. They only have a short window of time to find an available plantain, as their adult lives last only a week or two.

The eggs, laid on or near the plantains, hatch in about two weeks. From this point, the tiny larvae are in a race against time, as they munch on the plantains and rapidly grow. The larvae undergo three molts (instars) before reaching their fourth instar, where they enter a state of arrested development (diapause) and spend the long, hot, dry summer and fall under rocks and in cracks in the soil.

The larvae emerge from diapause when rains begin in November-December, feeding on native host plants — including the newly sprouted plantain as well as purple owl’s clover and exerted paintbrush. When the larvae reach their seventh instar, they pupate, and in two weeks, the adult butterflies emerge. They mate immediately, and the females begin laying egg masses. Nectar plants for the butterflies include California goldfields, tidy-tips, and desert parsley. The adult butterflies’ life span is only about ten days – so in every stage of development, key plants, particularly the diminutive plantain, must be closely aligned with the butterfly’s annual cycle.

Where to See Them

The most robust remaining populations of the Bay checkerspot butterfly are limited to only four or five areas of native grasslands on serpentine soils in Santa Clara County. If you visit one of these areas, look closely to find the dwarf plantain — an inconspicuous but essential key link in the butterfly’s life cycle.

Advocating for Survival

Green Foothills was a key player in advocating for the passage of the Santa Clara Valley Habitat Plan, in 2013 which serves as a framework for promoting the protection and recovery of natural resources for special status species including the Bay checkerspot butterfly. We also serve on the Public Advisory Committee for the Santa Clara Valley Habitat Agency which administers the Habitat Plan. We are grateful for the tireless research and conservation efforts of biologists to ensure the survival and recovery of this species.

As California experiences increasing intense and extensive periods of drought, we are hopeful that the interwoven life cycles of the plantain and butterfly will be resilient enough to adapt and survive.

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