Adult fleas live as parasites on warm-blooded mammals. Eggs are laid in batches of around 20, usually on the host. Therefore, areas where the host rests and sleeps becomes one of the primary habitats for eggs and developing fleas.
1 Additional Answer
Fleas are typically found outside in grassy areas. However, since these are so small it is very hard to locate even one of these. Also, they can be transferred from other animals You can find more information here: http://www.fleasmart.com/fleasrx.htm