What is the differance between 많이 and 많아?
What is the differance between 많이 and 많아? I am a little confused as i was told 많이 means to be many/very ie 많이배고파요! but then I saw 많아 used on its on in the line 아! 바퀴벌레! 아! 많아! 많아!

Why does he not say 아! 바퀴벌레! 아! 많이! 많이!..??

Question

What is the differance between 많이 and 많아? 
What is the differance between 많이 and 많아? I am a little confused as i was told 많이 means to be many/very ie 많이배고파요!  but then I saw  많아 used on its on in the line 아! 바퀴벌레! 아! 많아! 많아! 

Why does he not say 아! 바퀴벌레! 아! 많이! 많이!..??

Answer

In my humble opinion, basically, those are meaning of " enough, lots of, plenty of, many, much". 
But we don't say " 아! 바퀴벌레! 아! 많이!, because 많이 is adv.
많이 is adv. 많아 is adj.
So, you can say " 아! 바퀴벌레 왜 이렇게 많아! ( you should use adj at the end of the sentence.)
If you want to use "많이", you should say " 아! 바퀴벌레 왜 이렇게 많이 있어!".
Make sense? Cheers!!!!