PERSPECTIVES* Why do no specialized necrophagous species exist among aquatic insects? Stefano Fenoglio 1,4 , Richard W. Merritt 2,5 , and Kenneth W. Cummins 3,6 1 Department of Science and Technological Innovation, 11 Via Michel, University of Piemonte Orientale, 15121 Alessandria, Italy 2 Department of Entomology, Michigan State University, East Lansing, Michigan 48824 USA 3 P.O. Box 1181, Cooke City, Montana 59020 USA Abstract: Among terrestrial insects, there is a rich guild of specialized necrophagous taxa, i.e., that feed directly on carrion. These organisms constitute a significant functional component of terrestrial ecosystems, and have recently been extensively studied because of their importance in forensic entomology. Nothing similar exists in lotic environments, although paradoxically, insects are the most important group of invertebrates in streams and rivers, where they constitute up to 70 to 90% of benthic communities. We present some hypotheses as to why specialized necrophagous taxa have evolved among terrestrial, but not among aquatic insects. We suppose that the lack of specialized necrophagous aquatic insects was the result of many synergic evolutionary pressures, partly related to the distinctive physical features of lotic environments and partly to processes of competitive exclusion with other closely related arthropods. Keywords: necrophagous taxa, aquatic insects, carrion A rich and diverse fauna of specialized necrophagous or scavenger (i.e., feeding on carcasses) insects lives in ter- restrial environments. These organisms mostly belong to the orders Diptera and Coleoptera. They constitute an important functional component of terrestrial ecosystems and have been studied extensively because of their impor- tance in forensic entomology (Castner and Byrd 2009). Members of the families Calliphoridae, Sarcophagidae (Diptera), and Silphidae (Coleoptera), among others, are the result of a long evolutionary process that selected specialists in the detection and consumption of nonliving animal organic matter. Only a few examples exist (e.g., caddis larvae feeding on salmon carcasses) in lotic envi- ronments, although insects are the most important group of benthic invertebrates in streams and rivers (Merritt et al. 2008). Thirteen orders, almost ½ of those in the class Insecta, include species with aquatic or semiaquatic habits. In 5 of these orders, all taxa are aquatic (Merritt and Wallace 2009) with only terrestrial adults. In fact, aquatic insects exhibit high diversity and abundance, a broad distribution, and play a key role in the functional structure of running water ecosystems, where they oc- cupy almost all trophic niches (Giller and Malmqvist 1988) except one: no truly necrophagous aquatic insects have evolved functionally to feed entirely on carrion (Cast- ner and Byrd 2009). Compared to the large number of studies published in aquatic entomology in recent decades, the number of stud- ies dedicated to freshwater insects associated with animal carcasses is small (Merritt and Wallace 2010). Some in- vestigators have focused on the decomposition of salmo- nid carcasses primarily from Nearctic rivers with spawn- ing migrations of anadromous salmonids (Elliott 1997, Monaghan and Milner 2008a, b, c, Hocking et al. 2013). These carcasses are a significant source of organic mate- rial and inorganic nutrients in such streams (Wipfli et al. 1998, Chaloner and Wipfli 2002, Wipfli et al. 2003). Stud- ies of the decomposition process of trout carcasses in northern Italy were done by analyzing mass loss, coloniz- ing assemblages, and the importance of macro- and mi- *The PERSPECTIVES section of the journal is for the expression of new ideas, points of view, and comments on topics of interest to aquatic scientists. The editorial board invites new and original papers as well as comments on items already published in Freshwater Science. Format and style may be less formal than conventional research papers; massive data sets are not appropriate. Speculation is welcome if it is likely to stimulate worthwhile discussion. Alternative points of view should be instructive rather than merely contradictory or argumentative. All submissions will receive the usual reviews and editorial assessments. E-mail addresses: 4 fenoglio@unipmn.it; 5 merrittr@msu.edu; 6 kc8161@gmail.com DOI: 10.1086/677038. Received 20 October 2013; Accepted 10 January 2014; Published online 29 May 2014. Freshwater Science. 2014. 33(3):711–715. © 2014 by The Society for Freshwater Science. 711