In general, the aquatic insects of freshwater wetlands have been inadequately studied despite their apparent importance in wetland habitats, especially in energy and nutrient transfer. The Biological Survey of Canada (Terrestrial Arthropods) recognized the deficiencies in knowledge of taxonomy and ecology of insect species in wetland habitats and sponsored a "Conference on the aquatic insects of peatlands and marshes" in St. Andrews, New Brunswick, on 3 October, 1984. The Conference summarized current knowledge on the systematics and ecology of aquatic insects of Canadian peatlands and marshes, the wetland habitats chosen for emphasis, and sought to identify needs for research on the structure and dynamics of aquatic insect faunas in these habitats. The proceedings of the Conference are published here. The first two papers provide background information on the habitats under consideration and the interactions among invertebrates and vertebrates in these habitats. A second group of papers considers features of the Hydracarina, Ephemeroptera, Odonata, Hemiptera, Trichoptera, Coleoptera, and Diptera in peatlands and marshes. A final paper summarizes data on the occurrence of aquatic insects in bogs, fens, and marshes, addresses broader questions related to the nature of the insect fauna, and identifies needs for further research. By making accessible systematic and ecological information on aquatic insects of Canadian peatlands and marshes, the proceedings should support and encourage further work in these habitats.

Peatland development in Canada is influenced by climatic conditions, specifically a north–south temperature and an east–west precipitation gradient, resulting in specific and characteristic kinds of wetlands. The wetland classes (bogs, fens, marshes) are broad ecological units, each composed of distinctive groups of vegetation growing in appropriate habitats. Bogs usually develop in nutrient-poor areas where there is little movement of groundwater, whereas fens occur in more mineral-rich environments having a slowly moving water table. Marshes develop in areas that are periodically inundated by oxygen-rich water. Included within the peatlands are water environments ranging from small puddles to pools, each with a water quality that is influenced by the surrounding peatland.

This paper reviews the interactions of vertebrates and invertebrates in peatlands and marshes to assess current knowledge and future research needs. Living organisms may interact through a number of direct trophic and nutrient pathways and a variety of non-trophic, habitat-dependent relationships. Freshwater marshes and peatlands are dynamic aquatic environments and organisms that occupy these areas must be adapted to a wide range of environmental conditions. The avian community illustrates the main interactions of invertebrates and vertebrates in peatlands and marshes. Waterfowl, along with fish and furbearers, are the most economically important vertebrates using these habitats. Each of these groups has important trophic and habitat links to the invertebrates within wetlands.The most common interaction between vertebrates and invertebrates is the use of invertebrates as food by vertebrates. Few studies, however, have dealt with trophic dynamics or secondary production within wetlands. Waterfowl, fish, and many other wetland vertebrates, during all or part of their life cycles, regularly feed on invertebrates. Some invertebrates are vectors of disease and parasites to vertebrates. Vertebrates can directly affect the structural substrate that invertebrates depend on as habitat through consumption of macrophytes or through the use of living and dead plant material in the construction of houses and nests. Conversely, herbivorous invertebrates may directly affect the survival and distribution of macrophytes in wetlands. Macrophyte distribution, in turn, is an important factor in determining vertebrate use of wetlands. The general lack of both taxonomic and ecological information on invertebrates in wetlands is the main hindrance to future elucidation of vertebrate–invertebrate interactions in these environments. Development of invertebrate sampling techniques suitable for wetland habitats also is necessary. More specific research needs must be met to develop a better understanding of the structure and function of these dynamic systems.

Distributional, life-history, and ecological data on the water mite fauna of peatlands and marshes in Canada are reviewed and summarized. Just over 100 species representing 24 genera and 13 families are treated. The fauna comprises both residents of permanent water, often opportunistic generalists, and inhabitants of temporary water, typically highly specialized. A total of 35 species is reported from peatland habitats, including 30 from bogs and 17 from fens (12 are represented in both of these habitats), and 41 species from marshes. Inadequacies in the current data are identified, specifically incomplete zoogeographic data, uncertainty of species identifications, and poor definition of wetland habitats. Future projects are proposed to encourage research designed to improve knowledge of water mites in these habitats.

A search of literature on Ephemeroptera and Trichoptera of Canadian peatlands and marshes revealed only a few relevant studies which dealt mainly with emergence phenologies. Several species are listed in taxonomic and systematic works as being found in these wetland habitats, but because many of these records are the result of adult light trapping some doubt exists as to the actual habitat of the larvae.The Ephemeroptera and Trichoptera of peatlands and marshes in Canada appear to be part of a generalized fauna that also occurs in a wide variety of other habitats. Several species listed as occurring in peatlands and marshes also have been recorded in temporary pools. It is possible that adaptations for survival during the dry period in temporary pools also assist survival in many other habitats including the wetlands considered here.

The 196 species of Odonata known to occur in Canada are divided into two suborders: Zygoptera (52 species) and Anisoptera (144 species). None of these exclusively occupies marshes or fens. One zygopteran (Nehalennia gracilis Morse) is restricted to bogs whereas Coenagrion interrogatum (Hagen) predominantly occupies mossy bogs or fens. The following anisopterans solely, or predominantly, occupy bogs (with some occasionally in Carex marshes and (or) fens): Gomphaeschna furcillata (Say), Aeshna septentrionalis Burmeister, A. sitchensis Hagen, A. subarctica Walker, Williamsonia fletcheri Williamson, Somatochlora brevicincta Robert, S. franklini (Selys), S. incurvata Walker, S. sahlbergi Trybom, S. septentrionalis (Hagen), S. whitehousei Walker, Nannothemis bella (Uhler), and Leucorrhinia patricia Walker. Most of this information is based upon collections of adults, but studies of larvae are needed to determine the adaptations necessary for life in bog, fen, or marsh habitats.

Thirteen families containing 138 species of aquatic and semiaquatic Hemiptera have so far been recorded from Canada. The identification of these presents few real difficulties and so the general occurrence of the taxa across the country is fairly well known. Although there has been no intensive study of the Hemipterous insects in peatlands and marshes, the 61 species so far reported from marshes, 32 from fens, and the 33 from bogs appear to be facultative rather than obligatory inhabitants of these habitats. All have been found in other habitats and probably most lentic species occur in marsh habitats. All aquatic and semiaquatic bugs are predators, and most overwinter as adults. Environmental–physiological study of species occurring in bogs has just begun, but evidence suggests that many species have the ability to regulate their internal milieu in water with pH below 4.6–4.7. However, further experiments are needed to determine the physiological limits of tolerance of these insects, the details of osmotic and ionic regulation, and acid–base balance in low-pH water. More collecting is needed in bogs, fens, and marshes, and the life cycle and biology of the Hemiptera occurring in peat-lands still require intensive study.

A rich fauna of water beetles, comprising 11 families and 485 species, occurs in Canadian peatlands and marshes. These beetles are diverse with respect to morphology, feeding habits, life-history patterns, and even in the degree to which they occur in water. Major adaptations to peatland and marsh habitats are described. Based on species composition, the following regional communities of marsh-inhabiting beetles are recognized: arctic, boreal, Cordilleran, grasslands, and eastern temperate. Peatlands possess a community of beetles similar to that of boreal marshes but contain enough unique elements to warrant separate recognition. However, based on water beetle distribution, it is not possible to subdivide peatlands into bog and fen communities because these habitats have many species in common. Future needs for research on wetland water beetles are identified.

A review of the literature on biting flies of Canadian peatlands and marshes reveals that 21 species of Culicidae, 43 species of Tabanidae, and 6 species of Ceratopogonidae are known to occur in such habitats. Of these 70 species of biting flies, 45 occur in bogs, 22 in fens, and 36 in marshes. Although the species composition of wetland culicids is largely known, immatures of many species of the tabanids and ceratopogonids have yet to be collected and/or described. Almost nothing is known about the biology of the immature stages in wetland habitats. Most species known to inhabit wetlands have been recorded from both peatlands and marshes, but there are representatives of all families that appear to be restricted to a particular type of wetland. Compounding this paucity of information on the biting flies of Canadian wetlands is the inconsistency and lack of specificity in describing wetland habitats.

A survey of the literature has revealed that the Chironomidae are one of the most abundant and diverse groups of insects present in Canadian peatlands and marshes. A total of 104 named species of Chironomidae has been recorded from Canadian bogs, fens, and marshes. At least 207 species are present if all unnamed species are included in the total. However, until more information is available about the distribution of chironomid species, particularly those from fens, it is not possible to determine if any species (other than Metriocnemus knabi Coq.) are restricted to these habitats. Although several studies have been conducted in marshes and bog pools, the saturated peat habitats of fens and bogs have been little studied.

Most information on chironomids within peatlands and marshes is based on emergence trapping of adults, and there have been few attempts to study the ecologically important immature stages. Several aspects of chironomid ecology pertinent to peatlands and marshes are presented, based primarily on information gathered from other shallow-water habitats. The ecological and economic importance of chironomids within these habitats remains largely unknown. Most effort to date has been expended on faunal surveys, and any attempt to study chironomid ecology within peatlands and marshes would add greatly to existing knowledge.

Available information on the insect fauna of freshwater bogs, fens, and marshes is reviewed. These habitats are extensive and important in Canada. The fauna of marshes is diverse, and appears to consist chiefly of generally distributed lentic species. The fauna of bogs has some specialized elements, but most bog species are generalists. The fauna of Canadian fens is little known, but from limited data for a few groups appears to be moderately rich. Features expected in generalist and specialist species from peatlands and marshes are summarized, and the possible roles of insects in these ecosystems are outlined. Particular needs for future research include the following: careful definition of different kinds of wetland habitats; meticulous sampling of defined habitats to distinguish residents from incidental visitors; and detailed study of the life histories and habits of individual species. Further sampling, and studies of larvae, undoubtedly will increase the numbers of insects known from Canadian peatlands and marshes. About 4000 aquatic insect species are known from Canada. So far only 22% of the species in groups for which detailed information is available have been reported to occur in marshes, and only half as many in peatlands, even though some of the recorded species probably do not breed in all of the habitats from which they have been collected.