In severe cases of flea infestation, pet owners can see small insects crawling or jumping on their animal's body or crawling beneath its fur, according to PetMD. In less severe cases, pet owners might observe behavioral signs indicating infestation.
Behavioral signs of flea infestation include itching, scratching and general restlessness, according to PetMD. The animal may shake its head, scratch at its ears repeatedly or behave in an agitated manner. Owners might observe their pet chewing and licking one area of its body. An animal infested with fleas is unable to control the scratching on command. The pet owner may also notice that the animal is losing patches of hair, has an itchy rash or has scabs under its fur.
To locate signs of fleas, pet owners should run a flea comb through the animal's fur, looking carefully in the groin, armpits and other warm, protected areas of the animal's body where fleas prefer to hide, advises PetMD. Besides looking for actual fleas, owners should look for flea feces. "Flea dirt" appears as black, dark brown or reddish-brown specks. This is the digested blood excreted from the flea, so signs of flea dirt indicate the presence of fleas on the pet.