They develop on pasture and are eaten by the sheep. Larvae travel through the sheep's tissues to the lungs. Eggs laid in lung nodules, hatch and the larvae wriggle up the bronchi to the throat. They are swallowed and passed in faeces. The larvae infect snails or slugs in which they develop.
Infection occurs when the sheep eats a slug or snail.
Larvae travel through the tissues to the lungs. They are commonly found in frothy material within the bronchi. Eggs and larvae are also present. Usually identified on the appearance of grey spots 2-4 mm in diameter on the surface of the lung. The requirement for slugs and snails restricts Muellerius mainly to cool, mountain regions.