Canadian Tiger Swallowtail

These pictures were taken on July 22nd, 2009 in our back yard. They are a large butterfly measuring almost 4 inches and are one of the most common butterflies in Canada. Have you ever noticed how butterflies fly in a zig zag pattern and wonder why? If you think about it, their main predator is birds and if you look at butterflies, many have bite marks taken out of their wings. My feeling is that the zig zag pattern is to make it more difficult for birds to catch them.