Which insects have adults that are small and can cause itching due to their bites?

Fleas are small adult insects known for their ability to bite and cause itching in humans and pets. These tiny parasites feed on the blood of their hosts, and their bites can lead to allergic reactions characterized by intense itching and irritation. The size of adult fleas typically ranges around 1/8 inch, making them difficult to spot, but their presence can be felt through their bites.

In contrast, other options like moths, beetles, and termites do not typically cause itching from bites. Moths are primarily known for their damaging larvae rather than adult biting behavior, beetles vary widely in habits and do not commonly bite humans, and termites are social insects that primarily consume wood rather than engaging in biting behavior that affects humans. Therefore, the nature of flea bites and the resulting itching distinctly identifies them as the correct answer to the question posed.