Summer comes with the burden of fleas. How do you check for fleas? The easiest way is to routinely groom your cat. Using a "flea comb" which is a very fine-toothed comb can be very effective. The teeth on the comb are close enough together that fleas are caught between the prongs. The best place to check for fleas is over the back just in front of the tail. Also look for black "flea dirt" which is the bowel movement of the fleas. It looks like fresh ground pepper that sits on the skin.
For more information on fleas, please read Fleas in Cats.