Question about huge flies that keep popping up in my apartment?

I keep having these oversized flies popping up in my apartment complex. They are huge! Slightly smaller than a carpenter bee. I sprayed one and killed one this morning but here is my concern. I sure the fly is carrying maggots and I don't want maggots hatching in my apartment and getting on me or my dogs as this could be a health problem. Also it's cold and I can't figure out where they could be coming from. I thought flies came out in the summer?? I wasn't able to recover the dead fly this morning before I left for work but my fear is those maggots. Anyone has any suggestions?