The head is broad and flat, and the tail is square or very slightly notched. The jaws are heavy, and the lower mandible is longer than the upper. Spawning occurs in June and July in secluded hides and obscure places. These fish are nest builders, and parent fish guard the eggs and young. The young reach a length of from 2 to 6 inches the first year and are sexually mature in the third or fourth year of life.
Adults grow to enormous size.
The state record fish, that weighed 62 pounds, was taken from the Iowa River in Johnson County. Reports of huge flatheads of more than 100 pounds have been passed along through generation along the Mississippi River, but efforts to document their truth have been difficult and may be more river lore than factual. Flathead catfish are found principally in mud-bottomed areas and prefer deep waters in pools. They feed largely on insect larvae, crayfish, mollusks, fishes, worms, and terrestrial animals that wash into the streams. Small individuals, from 8 to 10 inches in length, have been observed feeding extensively on schools of young minnows in the shallow water.