Chasing the West Coast Lady

July 18, 2008

If butterfly watching sounds sedate, perhaps you’ve never witnessed the excitement of the territorial chase, in which males defend their chosen spots against male intruders. The west coast lady, a common Bay Area native, engages in chasing during the summer and can be seen in many habitats.

Afternoon is the best time to view this species’ fascinating behavior. Two factors dictate male west coast ladies’ behavior each afternoon: body temperature and defense of territory. Males stake out territory and will chase away other males and attempt to attract females, leading to showy flights that are fun to watch.

This species can be found in urban and suburban areas and is partial to the invasive cheeseweed plant. Attracted to open lots and spaces where cheeseweed and other mallow varieties grow, the west coast lady sprawls along with humans into any habitat but deep forest. In fact, the San Francisco Butterfly Count in 2007 had the national high for the species, which butterfly expert Liam O’Brien says is “probably reflective of the invasive cheeseweed, prolific in every vacant lot throughout our urban jungle.”

While these butterflies produce multiple generations of larvae, pupa, and adults year-round in our region, adults live longest in summer, when you’ll have the best opportunity to see them in action.

West coast ladies also use a variety of wing positions and choose perches specifically suited to helping them regulate their body temperature. You may see them on tree trunks, trails, walls, or some low foliage.

The wings of the west coast lady span between 1-1/2 and 2-1/4 inches and their tops feature brown and orange patterning, usually with an orange bar on each wing. If you spot this butterfly with its wings open, it is most likely cold, while wings closed over the back indicate a butterfly that’s too hot.

So watch the interplay between body position, temperature, and chasing, and you’ll get a good idea of a butterfly’s typical day

About the Author

Laura Hautala is a freelance reporter based in Oakland.

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