The common names of most Lepidoptera subfamilies are derived from the adults not the Caterpillars.
Swallowtail refers to the posterior extensions on the hind wings of some species.
Birdwing refers to the large wingspan of members of the Troides genus. The eggs are usually spherical and cream coloured. The Caterpillars of this family are very highly evolved. They live in the open. Simultaneously they emit a strong smelly secretion.