Direct Lifecycle vs Indirect Lifecycle
Parasites are small organisms that are notorious for living their complete lives in the body of larger animals, getting food and shelter from the host, and in some cases beneficial to their hosts. This is a wonderful ecosystem in itself where both benefit from each other’s existence. Had this been not so and these parasites caused harm to their hosts, their own existence would have come to an end. However, this is true for only some of the species of parasites as there are many that cause harm to their hosts eventually causing death of their hosts. Animals that harbor a parasite providing it with shelter and food is called a definitive host.
Now parasites are also simple as well as complex types. Simple parasites, once they get in the body of the host, live all their lives there, even reproducing in the process. This type of parasite is said to have a direct life cycle. However, in the case of complex parasites, they may require many hosts during their life cycle. This is mostly because of the need of reproduction. These parasites are said to have an indirect life cycle.
Thus it is clear that the life of a parasite can take many forms and it may depend upon exploitation of one or more hosts. Parasites that infect a single host and complete their lives with reproduction are said to have a direct life cycle. On the other hand, parasites that need to infect more than a single host mainly for the purpose of reproduction are said to have an indirect life cycle.
Parasites that infect a single host and complete their lives even reproducing are said to have a direct life cycle while parasites that need to have several hosts mainly for the purposes of reproduction have an indirect life cycle.