The most effective parasites are microscopic and very skilled at invading their hosts without being discovered. They could expel numbing secretions, which hinder the host from understanding that it is being attacked. Sometimes they are formed suitably to fit into the bodily part that they are destined for, and sometimes they are able to live outside of their hosts for extended periods of time.
Successful parasites may be able to assume the shape of latent eggs or cysts, which enables them to remain alive until their host of choice becomes accessible for invasion. This capacity is known as metamorphosis. For instance, there is a parasite with a thread-like body that lives in blood arteries, and there is also a parasite with a flattened body that lives in the intestines. Parasites often have suckers and hooks that prevent them from being ejected out of the host body or bodily part. These adaptations help parasites thrive in their natural environments.
According to a paper by Monash University, there is evidence that suggests the most successful parasites are those that are considered to be “generalists.” Generalist parasites are those that are able to infest a broad range of host species and are able to live in a number of distinct geographical conditions. Being able to occupy one host species while that species moves to a different place permits a parasite to spread to other species within the new area, hence increasing the number of sites and species in which the parasite may be found.