How do I know if I have fleas in my yard?  

If your area has alot of fleas, then yes you do need to treat your yard as well. You could get a flea on your shoe, pants or leg and bring it into your home. I hate fleas. Once you get infested with those wicked things, it is difficult to get rid of them. A few years ago we got them really bad. I hated to go to bed, they would just eat us up. I hate them! I swore that I would never have them again. We have kept on top of things and have never been infested agai.

I know this discussion is old, but I'd like to add something here. When I lived by a beach, I had sand fleas...really bad!! It was SO bad that my dog wouldn't even go into it's caged in area outside!! Sand fleas are NOT like regular fleas, they go for humans even more than regular fleas do. When I had the problem it was discussed with a veterinarian I knew in the area. His suggestion for the yard was THE best!!

Go to a gardening (or farm) store and buy agricultural lime. (It's really very inexpensive for a huge bag of it) If you know it's going to rain later on in the day, take your hand and walk up and down the lawn area hand spreading the lime lightly over the grass. When it rains, the lime dissolves and dissolves the body of the fleas. He also had me spread a thin line of lime around the foundation all the way around the house. I did this about once every couple of weeks, and eventually the flea population was nil. Besides getting rid of the flea problem, my lawn was the greenest, best looking one in the neighborhood lol. This is one of the best non-toxic ways I've ever dealt with fleas.