The threespine stickleback fish plays host to the tapeworm Schistocephulus solidus when the threespine stickleback is in a freshwater environment. These Schistocephulus solidus use their presence in the threespine stickleback fish in order to infect their desired prey: birds. In fact, infection with the Schistocephulus solidus causes the fish to behave in a different manner, which increases the chances that they will be eaten by the birds. In addition to behavioral changes, the Schistocephulus solidus causes the fish to lose melanin, making them more visible to the desired predators. Another physical change is that the Schistocephulus solidus appears to cause an increased rate of growth in infected fish.

             Ness and Foster investigated the relationship between infection with the Schistocephulus solidus and the threespine stickleback fish"s response to predators. Because the Schistocephulus solidus infects the fish in order to be transmitted to the birds that they target, they expected the fish to exhibit some changes after being infected with the Schistocephulus solidus. However, they were unsure whether those changes would cause the threespine stickleback to change their behavior in regard to all predators, or simply in regard to avian predators (Ness and Foster, 128). In order to determine the extent of the behavioral changes caused by Schistocephulus solidus infection, they simulated predators to determine whether the threespine stickleback"s response changed across predators. What they found was that infected threespine sticklebacks were less likely to respond to predators of any type, not just avian predators, than non-infected fish (Ness and Foster, 131-132). Furthermore, the scientists were able to dismiss the idea that positive buoyancy was the agent responsible for the behavioral changes in the infected threespine stickleback, but instead determined that the threespine stickleback moved more slowly after infection (Ness and Foster, 130-133).