"Clam" usually refers to insects, also known as vipers, beetles, and umbrella insects, which mainly live near water or in humid places. Clam refers to the larvae of cicada, which is the larval stage of an insect. They belong to the order Hemiptera.
Clammies are characterized by their small size and are usually found near water or on plants. Because it is not common in cities, most people don’t know much about clams.