Have you checked your crawlspace vents or access door lately to make sure they all open and shut properly and seal the opening closed? Torn screens on crawlspace vents and gaps around the vents and access door are ways that critters use to get into your crawlspace. Once in the crawlspace the uninvited guest may destroy insulation, air ducts, etc. Keeping them from getting in the crawlspace is the best solution. So take the time to walk around the house and just make sure everything is correct. This could save you a lot of hassle and money down the road.