The role of host-parasite interactions in the maintenance of biological diversity is potentially essential yet, it remains poorly studied or understood. Freshwater invertebrates such as odonates (dragonflies and damselflies) can be heavily parasitized and our research group is beginning to illuminate the factors determining parasite intensity (i.e. the number of parasite on any odonate individual). However, the consequence of such heavy parasitism on host fitness and host population size and host community structure is largely unknown. We propose to initiate a longitudinal study that will result in long-term time series of host and parasite populations and community trends. We further aim to develop experimental and observational approaches to quantify the consequences of intense parasitism on odonate growth, reproduction and mobility.