Most parasites, by definition, negatively affect the fitness of their host. In heavy infections, parasites can cause mortality. Parasites more often can cause a range of subclinical effects, such as reduced reproductive success, reduced lifespan, etc. There have been few studies where the effects of parasites on physical strength have been measured in animals. Devin's project is a test of the effect of nematode parasites (see figure below) on the body size and pulling strength of a common beetle, the bess beetle (Odontotaenius disjunctus).