The term FLY OR FLEA is an INSECT with six letters. The crossword solutions for this term are 'INSECT' and 'BUG'. Insects are small invertebrates that have a segmented body, jointed legs, and an exoskeleton. They are the most diverse group of animals on the planet, with over a million species identified. Fleas and flies are two of the most common types of insects. Fleas are small, wingless parasites that feed on the blood of mammals and birds. Flies are small, winged insects that can be found in almost any environment.