The Common swift (Apus apus), is a species of medium-sized swift, superficially similar to the barn swallow or house martin but somewhat larger. It is, however, completely unrelated to those passerine species, since swifts are in the separate order Apodiformes. The resemblances between the groups are due to convergent evolution reflecting similar life styles. The swifts' nearest relatives are thought to be the New World hummingbirds and the Southeast Asian treeswifts.