Which characteristic distinguishes merchant grain beetles from sawtooth grain beetles?

The distinguishing characteristic between merchant grain beetles and sawtooth grain beetles lies in the size of their eyes. Merchant grain beetles have relatively larger and more prominent eyes compared to sawtooth grain beetles. This feature can be a helpful identification marker when trying to differentiate between the two species, especially in grain storage situations where both may be present.

The other characteristics such as wing structure, body color, and leg length can sometimes overlap or vary within species, making them less reliable for accurate identification. For example, while color may vary due to factors such as age or environmental influences, and wing structures may look similar under certain conditions, the size of the eyes remains a consistent trait that can effectively help in identifying the specific beetle you are dealing with.