They could be scabs from something your cat is allergic to. I have a cat that has allergies, and gets scabs. Mine are not from fleas ...

I've been giving her some different food to see if it's a food allergy ... I've found out that she has less/no scabs if I feed her a fish based food vs. a chicken based food.

Could be mange, could be ringworm, could be scabies.

Could be places where another cat bit him, or he got nabbed by a predator and escaped.

Could be tick bites.

1/4 inch across is one heck of a big bug bite. Try putting antibiotic on half of them and a fungicide on the other half of them. See if one or the other clears up.

If he gets more and they don't clear up, I suggest a trip to the vet and a culture. Lots of skin diseases and different types of mites can be transmitted to humans. If the cat has something contagious, you want to get it treated, especially if you have kids.

Hmm, had him to vet, vet thought it was fleas. Not really concerned. But he just isn't healthy. his coat is dull, he sleeps in my lap a lot.
When I took him to vet, he had been doing a lot of weird coughing -- not the usual fur ball cough, but that cleared up.
I've put him on a new cat food, about a week ago, hoping that that will help.
And you're right, they are awful big marks. Raised, scabby, just ugly.

Sorry, sounds like you need a new vet. If he "just isn't healthy", find a different vet for a second opinion.

Probably needs worming, specifically tape worms, which is a two step process. You give the first dose, and EXACTLY 21 days later he gets the second dose. My cats just got wormed for tape worms, and their signs included being thin rather suddenly and odd coughing. Vet diagnosed from my relating problems. NOT taking 7 barn cats to the Vet!! Figured they got the tape worms from catching varmints around the barn, part of their job description! My job to keep them healthy. They do get cat chow daily as well.

Has cat been vaccinated for the common cat diseases? If it costs too much, you could vaccinate him yourself. Some of those diseases include coughing as a sign of problems. You just have to purchase the vaccines from one of the Vet supply catalogs. You will need two doses to get him started, then a yearly booster. I would strongly suggest you include Rabies vaccine in that yearly boostering list. Rabies shot protects YOU from him getting bitten by a carrier.

Our barn cats are very playful, like to "play bite" as you scratch bellies. They never bite down, but it only takes a small tooth scratch and saliva to infect YOU or children if cat is not vaccinated for Rabies. Rabies is a cheap vaccine and you won't need the treatment shots if you do get accidentally bitten or scratched.

The marks on your cat could be from a number of things, which other folks mentioned. For fleas, I see a dirtyish grey on the belly skin of animal like a dog. Might be harder to see on a cat with thick hair on all the body parts. Our barn cats are pretty tame, I would probably wash them using a flea soap to clean them up. Scabs seem to do well just being washed and having antibiotic ointment rubbed in. That method doesn't leave anything for cat to lick off later. With big or nasty holes, infections, I might treat the cat wounds/sores twice a day, the same way. Probably would lock cat up in my big dog crate in the barn or garage so I can be sure to locate him daily for treatment until his holes looked better.

I also would look for another Vet, this one is not very interested in keeping your animals cared for, or helping you to care for them well.

Sounds wormy to me too! And get some Cut-Heal for those scabby spots. It stinks but it will clear it up faster than other stuff! It heals from the inside out.
We get it where they sell horse supplies.