thoas swallowtail

[Chris Conlan]

It's almost certainly Papilio cresphontes if it looks like thoas and you
are in the Los Angeles area.  This species is resident in S. California and
feeds on citrus.  They seem to be more common from mid summer to fall.  If
you have citrus trees in the vicinity you might want to check for larvae
(look like a bird turd) or the large yellowish eggs usually deposited on
the upper side of the new growth.  Hope this helps

Chris