Korystina gracilis carried one of the most unusual head-protection devices in the London Clay weevils. The front edge of the pronotum projected forwards as a broad, flattened, slightly downcurved plate over the head, while a deep groove beneath the thorax received the rostrum. The result was a helmet-like shield above and a rostral socket below, concentrating much of the animal’s distinctive anatomy around protection of the head and snout.

No host plant or feeding trace is tied to the species. Its curculionid anatomy makes plant feeding likely, but a particular bark-, wood- or stem-boring habit would go beyond the evidence. The holotype preserves the head and thorax with the rostrum in its channel, whereas the second specimen is mainly a prothorax, so this remarkable protective mechanism is much better known than the rest of its biology.