Not a fan of symbolisms, but here's one:
If Fly has flown across your path;
Know that quick and abrupt changes in your thoughts, emotions and endeavors are afoot. Rapid changes in all aspects of your life are currently happening for you so be prepared to move quickly even in unfavorable and uncomfortable conditions. Fly can also signify an exponentially growing source of abundance is available for you right now. Use your keen eyesight to see the way. Never give up.
Alternatively this insect could be reminding you that your persistence in reaching your goals will bare fruit sooner than later. Even if it means annoying others or being selfish for a while – you do have the ability to accomplish your goals.