Neither egg or L3 stage can feed. When it is dry they desiccate. When it is hot larvae move about and exhaust their limited energy reserves. Their rate of movement is directly related to temperature. Most larvae and eggs survive freezing but some tropical parasites are frost tender.
Longest survival occurs under cool, moist conditions, such as occur in winter.
Under ideal conditions larvae can last a year. Hot, dry and windy conditions dry pastures out and kill larvae in just a few days. Larvae must be swallowed to infect the sheep. L3 on the leaves are most likely to be eaten, while those at the base of the herbage or in the soil are progressively less likely still. Because larvae migrate on a water film up leaves in the mornings and on dull days but go back down to the soil or pasture mat in the heat of the day, availability may vary during the day.