Gallagher fan huh? They are called flies because they do indeed fly but it would be pointless to call everything that flies that. The name tends to be given just to insects and only certain ones of those. You will notice that nothing is truly just called a fly unless it is for short or to describe mixed flying insects in one place. There are house flies, dragon flies, horse flies, sand flies etc. Mosquitoes are not usually called flies except as a generic term if they are mixed in with other types.
The reason fly is a reasonable term for them and not, say, birds or bats, is that insects are a lot smaller and much harder to differentiate exactly if there a lot of them around so a generic term is useful. Fish and birds are useful generic terms on their own whereas insects isn't a good term when you only mean the ones buzzing around and not the ones crawling on your food.
Last edited by Shagnasty; 01-05-2012 at 02:41 PM.