The food chain is a hierarchical series of organisms that are interrelated in their feeding habits. The chain starts when the smallest being like an insect is fed upon a larger prey species, which in turn feeds an even larger species. So if a species among the lower ranks of the chain has accumulated toxins such as pesticides or other organic chemicals, there is potential for these toxic substances to affect the species that prey upon them. This is the subject of new research conducted by the US Geological survey that found when fish feed on insects and when other wildlife species feed on fish, harmful contaminants are transferred up the line.