What did insects evolve from?

actually, prior to vertebrate fish, there were invertebrates, primarily arthropoda. Possibly the best examply would be the trilobyte, or the still-existent horseshoe crab. These creatures used a polysaccharide known as chitin to build form a protective exoskeleton. Their present day descendants include shrimp, , and lobsters (segmented crustaceans that carry semblance to insects) as well as all insects.