Karner Blue Butterfly
A tiny endangered butterfly depends completely on wild lupine as a caterpillar and on frequently disturbed, flower-rich barrens throughout its life cycle.
Artwork inspired by Ruth Grotenrath
Karner blue caterpillars can eat only wild lupine, a plant of sunny, sandy habitats maintained historically by fire and other disturbance. Eggs overwinter near the ground, spring larvae produce the first adult flight, and their offspring produce a second flight later in summer. Ants often tend larvae in exchange for sugary secretions.
Fire suppression, development, incompatible mowing, and fragmented habitat eliminated many populations. Wisconsin remains a major stronghold because public agencies, utilities, forest managers, and private landowners maintain connected lupine openings. Observe from paths, never collect, and avoid trampling lupine even when no adults are visible.
- Status
- Federally endangered
- Larval food
- Wild lupine only
- Habitat process
- Fire and disturbance
Quick guide
- Identify wild lupine
- Palmate leaves and blue flower spikes mark potential larval habitat on sandy, open ground
- Check both wing surfaces
- the underside’s orange crescents distinguish the butterfly at rest
Find the host plant before searching for blue wings
- Identify wild lupine
- Palmate leaves and blue flower spikes mark potential larval habitat on sandy, open ground.
- Check both wing surfaces
- Males flash violet-blue above; the underside’s orange crescents distinguish the butterfly at rest.
- Move slowly in openings
- Adults fly low and can disappear against sand and flowers after only a few meters.
- Protect the next generation
- Eggs and larvae may be present when adults are absent, so remain off lupine patches year-round.
Good to know
A blue butterfly in Wisconsin is not automatically a Karner blue; location, lupine habitat, size, and underside pattern all matter.
Notice these
- violet-blue male
- orange hindwing crescents
- wild lupine