The term mouse fly is kind of a contradiction and one of the types of flies that brings the word fly in fly fishing almost as far away from something flying as possible - still surpassed by shrimp flies not to mention crab flies, but anyway...
One of the reasons Britain became rich was because the Industrial Revolution (factories and such) got off the ground there sooner. Britain had a large navy, and many colonies in other parts of the world, such as India, and Rhodesia.
How were other nations able to catch up with Britain so quickly in the industrial revolution. Germany France and the US had more coal, iron and other resources than Britain and they had the advantage of following Britains lead. They borrowed British experts or technology. Germany and the US were the leaders.