Most species of flea have evolved specializations in order to be most effective at extracting blood from a specific host, such as a dog or a cat.
But if these fleas cannot find their specific host in their vicinity or nearby environment, they will be opportunistic and extract a blood meal from a human if they can find one.
That is why many pet owners whose home has become infested with cat fleas or dog fleas also find that they receive flea bites as well.
It is more difficult for fleas to bite humans because there are not many places on the human body for fleas to attach themselves and hide, as they would prefer to do. The hair and fur of animals is the perfect hiding place for fleas.
Humans will often be bit by fleas around the ankles and feet because they are in close proximity to the ground where the fleas are located.
