Observaciones de mherzig

A friend´s exterior house wall is covered with hundreds of butterfly(?) pupae (some type of Pieridae?).

Could you help me identify this species. I attach a long-shot of the group of insects and a close-up of one. They are at second floor level at the outskirts of Mexico city Weather has been changing a lot--hot, cool, warm, cold, breezy, rainy, just plain crazy. The house is probably above 2400 m altitude. House pets (dogs) use the mini garden below for their needs. The organisms all seem to be oriented in the same general direction. Is this kind of grouping common behavior for the species in question. I have seen trees covered by hundreds of pupae in a tent, but so far never attached to a wall in large numbers.

revoloteando en el jardín, de lejos pensé que era un colibrí. Estaba empezando a caer la tormenta (que a esta hora ya está instalada (14:20 hrs). Este año comparado con el pasado casi no han habido mariposas en mi jardín-¡que por cierto tiene más flores que el año pasado!

Not expecting to find any butterflies after 6 pm, I was caught by surprise at the appearance of what looks like a Parides photinus. Butterflies not being my field of expertise, I would appreciate confirmation of my ID. It seems to have a "swallow-tail", which the images I found for this species do show. It was photographed feeding on my zinnia; it never stopped fluttering its wings, so the image is somewhat blurry at the edges. The day was sunny and it had just stopped raining.