The term 'Diligent Insects' can be solved by the four-letter word 'ants'. Ants are a type of insect that are known for their hardworking nature and ability to work together in large groups. They are found in many different habitats around the world and are often seen carrying food back to their nests. Ants have been studied extensively by scientists, who have found that they are capable of complex behaviors such as communication and problem solving.