silly but serious..

ok, im a dork, i admit that lol but i have a question that has been bugging me for a few days..

i have this robo can right, you know, the cans that spray out the stuff that kill the insects and bugs n such.. well, the other day boy and i counted 20 flys on the roof in our living room, it was crazy! robo can works, i checked it and usually its very good at keeping the pests away but for some reason we had these flys on roof, so i closed the doors and thought ill get the little buggers.. next day they were all gone, where did they go???????? they should be lying dead on the floor but nope... does anyone else wonder this? its the same with moths! ya leave the door open and light on at night and in comes the moths, ya shut the doors and windows cos there a pest and then the next day there gone? where????? HELP! Its driving me nutssssss!