Successful parasites are small and adept at entering their hosts without being detected. They might release anesthetizing secretions that prevent the host from recognizing it is under attack. Sometimes they are shaped appropriately to fit into their destination body part, or they are able to survive outside their hosts for lengthy time periods.
Successful parasites may possess the ability to take on the form of dormant eggs or cysts, which enable them to stay alive until their target host becomes available for invasion. Examples include a flat-shaped parasite that invades intestines or one with a thread-like body that inhabits blood vessels. Suckers and hooks that keep them from being expelled out of the host body or body part also help parasites succeed in nature.
There is research suggesting that the most effective parasites are the so-called "generalists," reports Monash University. Generalist parasites are capable of invading a wide variety of host species, and they can thrive in several different geographical environments. Being a generalist enables a parasite to inhabit one host species while that species travels to a different area, then spread to other species within the new area, thus broadening the range of locations and species in which the parasite exists.