Threadworms spread by producing a lot of tiny eggs that can't be seen with the naked eye. When these eggs are swallowed, they hatch into worms in the gut. The female threadworms lay their eggs around the anus at night, which can cause an itchy bottom. Scratching the itch can lead to further infections if the skin is broken and can also spread the eggs through finger-and-nail contact. They can also be spread through direct contact, food, towels and bed linen. Threadworm eggs can also stick to clothing, carpets and vegetables. They are easily swallowed because of their small size and widespread presence.