Canadian peatlands can be classified into ombrotrophic bogs and minerotrophic fens, the latter subdivided into poor, moderate-rich, and extreme-rich fens, each with distinctive indicator species, acidity, alkalinity, and base cation content. If hydrology is considered the most important factor in peatland classification then the primary division must be between ombrotrophic bogs and minerotrophic fens; however both chemical and vegetational differences strongly indicate that the primary division of peatlands should be between acidic, Sphagnum-dominated bogs and poor fens on the one hand, and alkaline, brown-moss-dominated rich fens on the other. Although some metals such as sulphur and aluminum also vary along this gradient, nutrient contents of the surface waters do not. Bogs and fens are oligotrophic to mesotrophic wetlands that should be distinguished from eutrophic, non-peat-forming wetlands such as marshes and swamps by the presence in the former of a well-developed ground layer of bryophytes associated with relatively little seasonal water level fluctuation. Oligotrophy is probably maintained in bogs and poor fens by reduced water flow, whereas rich fens maintain mesotrophy by having larger water through-puts; however this is not well documented. Sphagnum appears to have real ecological significance, both in the initial stages of acidification and in controlling surface water temperature. Seasonal variation in surface water chemistry in all peatland types is relatively small, however precipitation events leading to changes in water levels do affect some chemical components. Although both autogenic and allogenic factors affect peatland development, initiation of peat formation and early development of peatlands during the Early and Mid Holocene were considerably influenced by regional climatic change. Later developmental patterns during the late Holocene and those seen at the present time appear to be more influenced by autogenic factors.

Taiga bog arachnids, mainly collected in pitfall or pan traps, are compared for two Manitoba regions, one southern and one northern. The dominant spider families in the south are Lycosidae, Clubionidae, and Erigonidae, whereas in the north they are Erigonidae, Lycosidae, Linyphiidae, and Gnaphosidae. The southern taiga bog has 82 species, the northern taiga, 39 species, with 16 species common to both regions. Two opilionid species were collected in the south and none in the north.

Six small peatlands, comprising three bogs and three fens, were surveyed for spiders in southern Ontario or southwestern Quebec. Collections from the Mer Bleue bog contained representatives of 108 species (54.6% of the total), those from the Crieff fen 97 (49.0%), those from the Wylde Lake bog 77 (38.9%), those from the Oliver bog 76 (38.4%), those from the Richmond fen 59 (29.8%), and those from the Poltimore fen 49 species (24.8% of the total). The family Erigonidae had 24.8% of the total 198 species, Lycosidae had 11.1%, Linyphiidae had 10.6%, and Salticidae had 9.1%, Web-building species outnumbered hunting species by 118 to 80. The majority of species in these peatlands are wide-ranging litter inhabitants, about one-third are tree, shrub, or herb inhabitants, and one-tenth were found only in or on the surface of the peat itself. Nine of the last-named group appear to be restricted to bogs, but none appear to be restricted to fens.

Peatlands were studied in temperate, boreal, subarctic, and arctic wetland regions of Quebec, mainly using pitfall traps. Altogether, 169 species of spiders, belonging to 14 families, were collected; 73 species were found only in the temperate-boreal region, 58 only in the subarctic-arctic region, and 38 in both regions. The most species-rich spider families were Linyphiidae (58.3% of all species), Lycosidae (12.4%), and Gnaphosidae (7.1%). Families occurring only, or mainly, in the temperate (and boreal) region were Hahniidae, Dictynidae, Salticidae, Liocranidae, and Theridiidae. Linyphiidae, especially Erigoninae, were typical of the subarctic region. Alopecosa aculeata (Clerck) and Pardosa hyperborea (Thorell) (Lycosidae), Theonoe stridula Crosby (Theridiidae), and Ceratinella brunnea Emerton (Linyphiidae) were found in six of the seven study areas. Seven of the eight opilionid species were found in the temperate region, but Mitopus morio (Fabricius) occurred only in the subarctic bogs. The only pseudoscorpion, Microbisium brunneum (Hagen), was caught in the temperate, boreal, and subarctic regions. The percentage of spiders collected in bogs of both Quebec and southern Ontario was 64% in the temperate region and only 27% in the subarctic region. Almost 50% of species from bogs in the Manitoba taiga were found also in Quebec. About a third of the Quebec bog spiders are Holarctic.

The terrestrial spider fauna of a North German bog relict, initially examined in a pitfall trap study in 1964–1965, was the subject of a similar examination 22 years later. Between the investigations the bog, which was still in a quite pristine state, had considerably changed its ecological character due to progressive draining. Sixty-eight spider species were collected. Many of them are characteristic for bogs, but none can be regarded as bog-specific. On a general species level no clear clues about consequences of biotope changes could be ascertained; 81% of the former species were found again.The most informative data are provided by species composition and abundance of the more prevalent spider species. In 1964–1965 the spider fauna was clearly dominated by photophilous species, many of them additionally preferring wet or moist biotopes. Twenty-two years later the proportion of photophilous species had decreased in favour of more skotophilous species.The scale of changes in biotope characters is regarded as the most probable explanation for this phenomenon, especially the increase of "shrubbiness" in vegetation and the nearly total loss of peatmosses. The spider Antistea elegans (Blw.), Hahniidae, is discussed as a possible indicator species for monitoring hydrological changes in bog biotopes.

This paper reviews and summarizes preliminary data on the taxonomy, distribution, and ecology of oribatid mites of Canadian peatlands, primarily those of eastern Canada. This fauna is a heterogenous assemblage comprising 71 species in 49 genera and 34 families, found in four main types of habitats: aquatic, mesic, xeric, and epigeal. About half of the oribatid fauna of peatlands, and most aquatic species, are restricted in distribution to the Nearctic. Oribatid taxa known or suspected to be parthenogenetic are much better represented in peatlands than in the general Canadian fauna. Data on the feeding habits of odonate larvae in Newfoundland bog pools, based on gut content analysis, show that oribatid mites, in particular species of Limnozetes Hull and Hydrozetes Berlese, are common prey of species of Aeshna Fabricius, Leucorrhina Brittinger, and Libellula L. A synopsis of available data suggests that assemblages of Limnozetes species may be useful in characterizing peatlands.

The peatlands of the northern Cordillera of North America (consisting of the mountain ranges and intermontane lowlands and plateaus of British Columbia, Alberta, the Northwest Territories, the Yukon, and Alaska) support a distinctive Odonata fauna. Forty species in six families and 12 genera are typical of northwestern peatlands and another 12 species are occasional inhabitants of these environments. Of the 40 species, eight (20%) are peatland obligates and four (10%) almost always occur in such habitats. The remaining 28 (70%) are generalists and live in a wide range of aquatic habitats; nevertheless, they often are common inhabitants of, or are even dominant in, peatland environments. The fauna is dominated by the genera Aeshna Fabricius and Somatochlora Selys, with 11 and 10 species, respectively. It is also dominated by species restricted to Boreal regions (25 species, 62.5%), six (15%) of which have Holarctic distributions. The remainder of the fauna consists of eight species (20%) ranging transcontinentally in Transition Zone forests south of the Boreal Forest, five (12.5%) restricted to the Cordillera, and two (5%) with wide distributions in North America. Notes and maps summarize our knowledge of biogeographical information and previously unpublished records are listed. Significant southerly range extensions for species such as Coenagrion interrogatum (Hagen), Aeshna septentrionalis Burmeister, A. sitchensis Hagen, A. subarctica Walker, Somatochlora septentrionalis (Hagen), and Leucorrhinia patricia Walker are reported. Ecological and natural history data are outlined for each species. There do not appear to be any clear differences between the faunas of bogs and fens; dragonflies seem to respond to the habitat's form and structure rather than to its acidity or nutrient levels. Distinctive species associations result. A better understanding of the preferences of these dragonflies for different peatland microhabitats must await detailed research on oviposition behaviour and larval ecology.

The world species of Limotettix Sahlberg are reviewed, and 13 new Nearctic species are described: in the typical subgenus — L. conservatus; in the new subgenus Dryola — L. elegans, L. minuendus; in subgenus Neodrylix — L. urnura; in subgenus Ophiolix — L. nigristriatus, L. pseudosphagneticus, L. xanthus; and in subgenus Scleroracus — L. brooksi, L. medleri, L. obesura, L. scudderi, L. strictus, and L. zacki. Limotettix (L.) emeljanovi is proposed to replace L. luteolus Emel'janov, 1962, nec L. (Scleroracus) luteolus (Sleesman, 1930). The 80 known world species are arranged phylogenetically. From this analysis the genus evidently evolved in the New World from swale and fen inhabiting ancestors that fed on spike-rush. Their bog-inhabiting descendents fed on various rushes and sedges, but apomorphic lineages transferred to ericaceous plants. Adaptation to ericaceous plants permitted invasion of drier habitats, with subsequent radiation on other semiwoody plants, principally Asteraceae and Symphoricarpos.

Relative abundance of Nicrophorus species sampled with pitfall traps varies between habitats and seasons in the Mer Bleue bog area near Ottawa, Canada. Baited pitfall trapping is useful in studying habitat associations but does not accurately sample reproductively active species. Nicrophorus sayi Laporte is a spring breeding species associated with stands of mature forest. Nicrophorus orbicollis Say and N. tomentosus Weber were taken at baited pitfall traps in all habitats. Nicrophorus defodiens Mannerheim and N. vespilloides Herbst were found primarily in forest and bog habitats, respectively, and did not reproduce outside of these habitats.

During the period 1985–1989, the carabid assemblages of a raised peat bog in eastern central Sweden and of six peatlands in New York State and Maine were studied. The principal methods of investigation were pitfall trapping in summer, and quadrat sampling in winter. In addition to carabids, potential food organisms were evaluated from the pitfall catches.The bogs, although of different types and located on different continents, show similar physiognomic vegetation units. Eight of these units are considered relevant as carabid microhabitats. The carabid assemblages of open sunny, and wooded shaded habitats are clearly distinguished. Only a few species are adapted to the extreme environment of open Sphagnum L. habitats. Among them, stenotopic species are dominant. The seasonal distribution of two species on Swedish Ryggmossen [Agonum ericeti (Panzer), Pterostichus rhaeticus Heer] suggests that the carabids of open bog plateau habitats use damp Sphagnum lawns for their summer activities and migrate to drier hummocks for overwintering.On bog plateaus, larger populations of ground beetles were only found where a pronounced pattern of hummocks and hollows exists. In bogs with a prevailing uniform vegetation of Sphagnum mats, carabids were conspicuously scarce. Thus, the development of a bog indigenous carabid fauna is closely related to the presence of a hummock–hollow mosaic. The data indicate that in most bog habitats food is not a limited resource and does not play a key role as a population controlling factor.

The beetle (Coleoptera) fauna of a black spruce [Picea mariana (Mill.) BSP] – tamarack [Larix laricina (DuRoi) K. Koch] – Sphagnum bog in Algonquin Provincial Park, Ontario, was sampled from early June to mid-August with yellow pan traps and emergence traps. The yield was 5734 beetles, in 30 families. Ptiliidae was the most numerically abundant and Staphylinidae was the most taxonomically diverse. Carabidae was second in diversity and third in numerical abundance. The abundance and ecological implications of some individual species are discussed. Few of the species are bog-specific. The faunal composition suggests that the bog is in a late-succession phase and that most of the beetle species are derived from adjacent habitats.

Seventy-three species of the acalyptrate family Sphaeroceridae are recorded from Canadian peatlands, largely on the basis of pan trap samples from peatlands in southern Ontario, the Yukon, and Alberta. Spelobia nana (Rondani), Spelobia ibrida (Roháček), and Trachyopella atomus (Rondani) are newly recorded from North America. Fifteen species are identified as characteristic of peatlands, and their distributions and relationships are discussed. Southern peatland populations of several of these species are interpreted as relict populations in peatlands serving as post-Pleistocene refugia. Some species are known so far only from peatlands along the postglacial fringe.

The Wagner Natural Area, located 8 km west of Edmonton, Alberta (53°34′N 113°47′W), contains a boreal spring fen estimated to be 4700 years old. The site was selected in 1985 for a survey of its arthropod fauna. A transect of the site from marl pools through fen, edge effect, and treed swamp was sampled for arthropods using pan and Malaise traps. Specialized microhabitats outside the transect were identified and sampled using pan traps. The Wagner fen samples contain 2181 species of arthropods contributing to a total known biota of 2905 species in the peatland. Of those, 1410 are Hymenoptera. Although seven other peatland studies are known, the inability of systematists to name most species prevents direct comparisons among peatlands. Data obtained from the Hymenoptera collections at Wagner demonstrate a progression in species richness as one approaches the forest–fen edge from either fen or forest. A large proportion [30% (382 species)] of Hymenoptera species, termed the aerial component, is active both in the forest–fen edge and in the fen. The aerial component is a highly mobile, at least locally transient, but often uncollected component of peatland ecosystems. Presence of the aerial component is probably associated with habitat structure. Those peatlands possessing more complex vegetation architecture have greater proportions of aerial species. About 80% of Hymenoptera at Wagner are parasitoids, most of which attack larva of holometabolous hosts. Based on the host groups sought by parasitoids and the ratio of parasitoid species per host species, the fen is estimated to contain about 6000 species of arthropods.

This report is a synopsis of the terrestrial arthropod faunas collected from four peatlands in southern Ontario. The peatlands surveyed were the Wylde Lake bog (43°55′N, 80°30′W), Crieff fen (43°25′N, 80°07′W), Oliver bog (43°20′N, 80°16′W), and the Wainfleet bog (42°55′N, 79°17′W). Arthropods were collected in yellow pan traps (aluminum pan traps at Wainfleet) during the period May 1987 to June 1988 (including the period of snow cover from December to March). A total of 33 029 specimens were removed from the pan trap samples and of these 17 173 individuals were assigned to species. Between 603 and 870 species of arthropods were identified from each site. Collections from each site were compared using taxonomic and ecological groupings (based on feeding behaviour and habitat preference) of species. Sorensen's Index of Similarity was used to compare the overlap of species among sites. The Hymenoptera, Diptera, Coleoptera, and Araneae were the most species-rich orders collected at each site. More species preferring peatlands were collected at each of the three undisturbed peatlands (Wylde L., Crieff, and Oliver) than at the mined bog, Wainfleet. Species not usually associated with peatlands were more numerous in the Wainfleet collection than in collections from the undisturbed sites. It is concluded that grouping of species by habitat preference is a useful technique for assessing habitat disturbance.

Two behavioural extraction techniques, wet and dry extraction, were evaluated as to their relative efficiencies in removing invertebrates from samples of wet peat collected from a fen near Schefferville, Quebec. Dry extraction involved drying a substrate sample from above, forcing any macroinvertebrates contained therein to move downward out of the substrate matrix. In wet extraction, peat samples were suspended in a water bath where a vertical temperature-dissolved oxygen gradient had been established; invertebrates responded to the gradient by moving downward out of the sample and into the water bath. Wet extraction yielded approximately three times more invertebrates per unit volume of substrate than dry extraction, but the two extraction methods differed considerably in their ability to extract different invertebrate taxa. Dry extraction was more effective than wet for obtaining larvae of Tabanidae, Tipulidae, Empididae, and Dolichopodidae, but larval Chironomidae, sphaeriid clams, and oligochaete worms were collected more efficiently by wet extraction. Other invertebrate taxa were collected with approximately equal efficiency by both methods.