Where do fleas go when it gets cold outside?

During the winter fleas tend to seek the nearest source of warmth. It can be in a house, or on pets. Each flea can lay up to 20,000 microscopic eggs everyday. If you see a flea on your pet, then its a safe bet that in a week or so there will be thousands more. I would recommend if you have pets, strictly indoor or not, that they be on a year round flea and tick prevention.