Molecular and morphological work through the 2000s placed termites firmly within Blattodea, as the epifamily Termitoidae, nested among cockroaches rather than beside them. Their closest living relatives are Cryptocercus, subsocial cockroaches that live in family groups in rotting logs and pass gut symbionts to their young. Ants, by contrast, are wasps: they belong to Hymenoptera, a different order entirely.
The convergence runs deep, which is why the confusion persisted. Both groups evolved sterile worker castes, large colonies, chemical trails and nest architecture. But the differences are diagnostic. Termite workers include both sexes and are immature individuals that continue developing; ant workers are all adult females. Termites have straight, beaded antennae and a broad waist; ants have elbowed antennae and a pinched one. Termites undergo incomplete metamorphosis with no pupal stage.
What termites do not do is digest wood unaided. Lower termites such as Reticulitermes rely on gut protists and bacteria inherited by feeding on nestmates, which is why a termite isolated from its colony starves on a diet of pure wood.