Maggot Problem!!! HELP!!!!?

hi..um my mom was cleaning out our van and she can acros a maggot. se tried vaing it up (iut was inbetween the garage floor and cement) more came up..i jst wanted to know why they might be there and how we can get rid of them..i think that they are pobably laying eggs under the garage floor and there are lots more under there....has anyone else ever had this problem before??!?!?! HELP!