When is an all-white butterfly not a cabbage butterfly?

Comparing white butterflies - I believe the underlying image is a Margined White.

I must admit to thinking that every white butterfly I see flitting around is a Cabbage butterfly, also called the Cabbage White (upper left inset).  However, yesterday I encountered a white butterfly without the tell-tale black spots on the wings.  Could it be a mutation?

As it turns out, no.  There are a number of all-white butterflies.  Many of them, such as the West Virginia White (lower right inset), are natives of eastern North America and do not come close to British Columbia.  The Margined White butterfly (lower left inset) does.  The lacking wing spots and the presence of a gray edging on the forewing leads me to believe that I photographed a Margined White.  However, other photos of the Margined White butterfly have shown them with a lot of gray edging about the wing veins (click here to see), so I am not completely sure of the identification.

Compounding the issue is that there seems to be a seasonal polymorphism in the species that I am trying to understand.  The spring versions of the butterfly tend to have a heavy dusting along the wing veins while the summer variety is more white as in the photos shown above.  It could be that this is an insect that requires more study and the information on it is not quite clear.  What I do know is that there is limited data on the subject to give me a clear idea of what exactly it was I saw and photographed.  I guess I will have to look into it more when I have time and if my curiosity is piqued.  I have already spent a lot of time researching it.

As always, thanks for reading.

Eric Svendsen     www.ericspix.com