Expert: Walter Hintz - 1/11/2006

Question
Are there any examples of symbiotic relationships that are initially mutualistic (good for both species), but as time goes on and the individuals age, one of the species becomes a parasite harming or destroying the other?

Thank you.

Answer
Hi John;
 According to those who study the biology of parasitism most parasite-host relationships began as commensalism or mutualism.  A mutualistic relationship changes when one day one organism starts taking a bit of energy from the other and the parasitism begins.  
Incidentally a "good parasite" does not kill the host because if it does it dies also.