Island Marble Butterfly
Island Marble Butterfly is a small white butterfly marbled with greenish-gray patterning beneath the hindwing and is most meaningfully sought in open prairie-like habitat, dunes, and coastal lagoon edges with mustard-family host plants.
Artwork inspired by Barbara Earl Thomas
Island Marble is a small white butterfly whose greenish marbling beneath the hindwing is more useful than brightness alone. Its surviving San Juan Island habitat combines open coastal prairie, dunes, lagoon edges, and mustard-family larval host plants.
Adults are most visible from April into June, but the federally endangered population is extremely restricted. Observe from signed routes, record both wing pattern and habitat, and never enter host-plant patches for a photograph.
- Primary range
- Washington
- Habitat
- open prairie-like habitat, dunes, and coastal lagoon edges with mustard-family host
- Status
- Federally endangered
Quick guide
- Overall clue
- A small white butterfly marbled with greenish-gray patterning beneath the hindwing
- Then confirm
- April–June on San Juan Island
Confirm Island Marble Butterfly without disturbance
- Check the underside pattern
- Wait for a perched butterfly and look for greenish-gray marbling beneath the hindwing rather than relying on a flash of white in flight.
- Compare size and posture
- Use the compact body, wing shape, and resting position to separate Island Marble from other whites seen in coastal light.
- Confirm habitat and season
- Pair an April–June observation with open San Juan Island prairie, dune, or lagoon-edge habitat containing mustard-family hosts.
- Protect the only population
- Stay on the signed trail, use zoom, avoid host plants, and withhold precise coordinates from public posts.
Good to know
Remain on designated paths, avoid trampling mustard host plants, and never publish the precise location of an encounter.
Notice these
- A small white butterfly marbled with greenish-gray patterning beneath the hindwing
- open prairie-like habitat, dunes, and coastal lagoon edges with mustard-family host plants
- April–June on San Juan Island