Physical Characteristics Ascaris lumbricoides are large, pale white or pink worms that can grow up to 12 inches (31 cm) long in humans, making these some of the biggest intestinal nematodes around.

In this 1960 photograph are two, Ascaris lumbricoides nematodes, i.e., roundworms. The larger of the two is the female of the species, while the normally smaller male is on the right.