Parasites are organisms that benefit from harming other organisms. The organism they profit from is usually called host. Many parasites have complex life cycles, where they need different hosts for different stages of their development. As an example, the cycle egg > snail host > mammal host is common for parasites of herbivorous mammals. Malaria is caused by single-celled parasites. These parasites go through two stages in their development. One stage is in the blood of mosquitoes, the other in the blood of humans.