Tongue Worms: Pentastomida

Tongue worms usually need to complete their life cycle in more than one host. Larval hosts are called intermediate hosts, while the hosts of adults are called definitive hosts. An intermediate host accidentally swallows the eggs as they eat. The larvae hatch and infect the tissues and organs of the intermediate host. They molt, or shed their exoskeletons, several times before reaching the infective stage of their life cycle. The infective stage is a dormant, or resting, stage, and the larvae are surrounded by a non-living, protective covering called a cyst (sist). The larvae break out of the cyst when another animal, the definitive host, eats the intermediate host and its cysts. In most species, the larvae first burrow into the lining of the intestines or stomach of their definitive host. Later, they move into the body cavity before tunneling into the lung.

Both males and females are required for reproduction. Mating occurs when the males and females are about the same size. Females store the sperm in their bodies. Mated females increase in size as their bodies fill up with developing eggs. Hundreds of thousands to millions of eggs are produced and released continuously. Eggs released in the lungs are coughed up by the definitive host, swallowed, and then passed out of the body with the solid waste. The eggs of species that live in the nose and its sinuses are sneezed out or swallowed and passed out of the body with the solid waste.