Well, Luke, there are many ways to answer that question. In virtually all ant colonies the queen is the largest member, and none are larger than those of the African driver ants in the genus Dorylus, measuring more than 4 cm long. Colonies of this species may include many millions of individuals, all of which are laid by one massive queen. Males of this genus are almost as long (~3 cm) and more robust than queens. Commonly known as "sausage flies" for their characteristically long and bloated abdomen, males disperse from their natal nest in search of other colonies, which drag the male into the nest to mate with virgin queens.
Several species may claim to have the largest workers, including the "dinosaur ants" in the genus Dinoponera from South America and Camponotus gigas of Southeast Asia, each measuring about 3 cm. Just slightly smaller than these two giants is the notorious bullet ant (Paraponera clavata) of Central and South America, so-called for its excruciating sting.
Perhaps the largest ant ever is the extinct Formicium giganteum from the Eocene (about 46 million years ago), whose queen measured 5.5 cm long with a 13 cm wingspan - larger than a ruby-throated hummingbird. By comparison, the smallest workers in the ant genus Carebara can be smaller than a pinhead (< 1 mm)!
- Tim O'Connor & the AntAsk team