[The Lone Ranger]

Ironically, perhaps, modern insects appear to be descended from aquatic (specifically, freshwater) ancestors. Insect wings appear to be modified gill covers. Of course, many insects are aquatic as larvae, but only a few are aquatic as adults. And, of course, virtually none are marine.


Well before modern insects evolved, there were crustaceans occupying pretty-much any marine niche that could be occupied by an insect. Indeed, crustaceans are a far, far more abundant and diverse group of organisms than most people realize -- malacostracans, cirripedes, remipedes, decapods, euphasids, etc., etc., etc.


One of the most basic of ecological principles is the "Competitive Exclusion Principle." Briefly stated, it maintains that no two species can occupy the same ecological niche.

So at a guess, I'd say that the reason there are so few marine insects is because virtually any niche that could be occupied by a marine insect is already occupied by some crustacean or other.


Cheers,

Michael