It remains quite cold here in Big Valley (Modoc County CA) and only a very few wildflowers are blooming. Yet on sunny afternoons many “white butterflies” can be seen flitting about. What are these butterflies doing so early in the season? The butterflies in question are western whites (Pontia occidentalis).
Western white butterflies are found throughout the Western United States, especially at higher elevations. They overwinter in the chrysalis or pupal stage and emerge very early in the spring. The host plants for western white butterflies are members of the mustard or Brassica family. The females lay their eggs singly on the host plants, which the larvae eat upon hatching. One of the earliest blooming wildflowers in our area is dagger pod (Phoenicaulis cheiranthoides), a member of the mustard family. This early flying butterfly drinks the dagger pod nectar and can also lay the eggs of its first brood on the same plant. Later in the season, as other mustard species grow and flower, the western white can begin to utilize them. This butterfly is well adapted to get an early start on the summer breeding season.
I previously did a post on the western white (“Western White” 06-10-2013). Western whites are quite variable. However, I believe these pictures better show the upper side forewing margin, which is lighter than the submarginal stripe. On the underside, the hind wing veins are outlined in greyish green and the forewing tips also have the same coloration. In one picture the butterfly can be seen inserting its proboscis into the dagger pod flower.
Before long other butterfly species will join their western white cousins.