Are flies insects?

Yes. So are ants, bees, ladybugs, mosquitoes, butterflies, moths—and about one million other kinds of small animals. All adult insects have three parts to their body: head, thorax, and abdomen. The head has the eyes, mouth parts, and two antennae, or feelers. On the thorax most insects have six legs and either two or four wings. The abdomen is where the insect digests food and breathes. Even with these three parts, most insects are less than 1/4 inch (6.4 mm) long.