What is a visible characteristic of Bostrichid beetles?

Bostrichid beetles, commonly known as pinhole borers, have a distinctive morphology that is characterized by their head being typically concealed from view. This is due to the shape and positioning of their bodies, which often leads to the head being obscured by the thorax. Such structural adaptations facilitate their burrowing behavior as they create small holes in wood, where they dwell and feed.

The other characteristics mentioned in the choices do not accurately define Bostrichid beetles. While some insects have distinct head shapes that are always visible or present certain antennal features, those do not apply to the Bostrichidae family. Their flat bodies and wing structures might resemble other beetles, but the specific visibility of their head is a hallmark trait of this group.