Most sheep parasites have direct life cycles. The adult parasite with a direct life cycle resides inside the host animal from which eggs are shed into the environment. Ingestion of this immature stage of the parasite allows the life cycle to proceed. An intermediate host, such as an insect, is required for parasites with an indirect life cycle. Examples include the tapeworms, Moniezia , and Thysanosoma .
Infective larvae develop inside the intermediate host.
These insects containing the larvae are then consumed by the primary host animal. Several topics relating to parasite life cycles need to be addressed to apply this knowledge in prevention and control programs. Seasonal Development of Infective Larvae Peak infective levels of larvae on contaminated pasture occur during late summer and fall. It may be most beneficial to use dewormers early in the grazing season to prevent escalation of the worm problem. Some parasites may overwinter on pastures.