Final answer:
The missing category of termites in the United States is 'subterranean.' Termites can digest wood due to a mutualistic relationship with protozoa and archaea in their guts, and they are known for their complex social behaviors within colonies.
Step-by-step explanation:
Termites found in the United States are generally grouped into three categories: drywood, dampwood, and subterranean.
Termites are remarkable insects capable of digesting wood thanks to their ability to form a mutualistic relationship with microorganisms residing in their guts. In their digestive system, symbiotic protozoa and archaea produce enzymes that break down the cellulose found in wood into smaller, usable carbohydrate molecules. This process is vital for their nutrition and survival, as these enzymes allow termites to extract energy from the wood they consume.
Insects, like termites, often exhibit complex social behaviors and live in large, well-organized colonies. They divide the labor among different specialized individuals, ranging from those that reproduce to those that gather food or defend the nest. Termites are among these social insects, working collectively in a highly structured society.