A common, single-brooded Legume feeder found from sea level (where it flies in March and April) to above tree-line (early summer). There is plenty of variability, especially in the size of the black spots beneath (smaller in colder climates) and in the amount of blue on females above (none to a lot). Local populations tend to specialize on particular host plants. In the Central Valley and lower foothills occurs an "ecotype," or ecological race, adapted to naturalized annual Vetches much used on highway embankments.

Rare and seldom recorded on our transect; tends to be very local, and its habitat preferences are not well understood. It occurs in rocky canyons and mixed mesic forest at mid-elevation, and also at or near tree-line--the one constant is its association with perennial lupines, but they of course are much more widespread and common than the Arrowhead Blue is!