mice in the air

I was experiencing some laggin in throttle response. I asked my dad about it. He said to check the fuel,and air filter. I decided to buy a new airfilter,fuelfilter,oil filter and 5 quarts of oil. WHen to put in the easiest first, the oild filter. Opend up the airbox took out filter and BAM 2 dead fucking mice. one was like all skeleton, and the other must have just died. they crawled in through the part where it sucks the air in from. I think I am going to put some screen on it till I make my cold air intake.