Allowing livestock access to wetlands directly impacts their traffic and excretion to the surface water and riparian areas, and the use of deworming drugs results in manure containing a range of pesticides that may affect its decomposition by invertebrates. Hydrophobic anthelmintic drug residues are excreted in cattle manure and have been shown to exert non-target effects on invertebrate fauna that encounter dung as a part of their lifecycle, but the aquatic macroinvertebrate food web associated with manure decomposition and interactions with anthelmintics are not well understood. The goal of this study is to determine which macroinvertebrates colonize manure in an aquatic system and how it alters rates of decomposition of manure deposited into water. Secondly, to assess the implications of anthelmintic use in beef cattle on manure breakdown and colonization by macroinvertebrates in aquatic ecosystems. Invertebrate access to manure was shown to have a significant effect on the rate of decomposition by day one of the study. By day five of decomposition, manure that was open to invertebrate access had been completely consumed while manure was still retained in samples that restricted access to manure from invertebrates until the end of the experiment on day 35. Manure colonization was dominated by two taxa (>97.5%), nonbiting midge larvae (Chironomidae) and freshwater shrimp (Hyalella azteca). The preservation of wetlands is dependent on an understanding of all factors that impact the function and health of the ecosystem and its users. Moreover, the success of Best Management Practices for cattle grazing depends on a knowledge base of food web responses. An insight into the invertebrate species using manure deposited in waterways and the implications of deworming treatments on this process provided by this study will help best inform these practices.