Since Lindquist et al. (1979), many molecular markers (e.g., ITS, COI, 16S, 18S, 28S) have been used to help elucidate species boundaries in the Acari (Navajas and Fenton 2000, Cruickshank 2002, Navajas and Navia 2010, dos Santos and Tixier 2017, Lehmitz and Decker 2017). In particular, the 658 bp ‘barcode’ region of COI (cytochrome c oxidase subunit I) has been promoted as a reliable determinant of species boundaries in animals (Hebert et al. 2003); however, compared to other arthropod groups (Virgilio et al. 2010, Wilson et al. 2017), the paucity of barcode data available for Acari worldwide is striking (e.g., Navajas and Navia 2010). This also applies to Canada, where 70–80% of all named Canadian Lepidoptera, Coleoptera and Araneae have been barcoded and assigned BINs, with each BIN representing a ‘barcode cluster’ for a putative species (Ratnasingham and Hebert 2013, Blagoev et al. 2015, Brunke et al. 2019, Pohl et al. 2019), whereas fewer than 10% of named Acari have assigned BINs. Nevertheless, 7462 BINs from 189 families have been sequenced for Canadian Acari (Tables 1–6; available in BOLD). Interestingly, the BIN richness is well above past and present predictions of species richness for many families in Canada (see further notes in respective taxonomic sections below; Lindquist et al. 1979). Note also that available BINs are based on a limited number of samples, habitats and hosts surveyed. For instance, ~900 of these BINs were generated from a single barcode study of mites at one location in subarctic Canada (Young et al. 2012).

Because of variation in mutation rates among mite taxa, variable retention of ancestral polymorphisms, and past hybridization events, the BIN algorithm may overestimate species richness in some groups. High intraspecific divergences in mites (7–20%) have been observed in some cases (e.g., Heethoff et al. 2007, Niedbała and Dabert 2013, Rosenberger et al. 2013, Zhang and Zhang 2014), possibly reflecting higher rates of mitochondrial evolution in mites than in most other animal taxa (Young and Hebert 2015), or long-term consequences of reproductive systems such as haplodiploidy (Tixier et al. 2017) and thelytoky (Palmer and Norton 1992). On the other hand, it is plausible that cases of high BIN richness, at least in part, reflect cryptic diversity that is not yet resolved morphologically (e.g., Ratnasingham and Hebert 2013, Ondrejicka et al. 2016). Indeed, species distinguished by only minor morphological differences, or cryptic species, are common and sometimes associated with narrower host ranges than previously thought (Knee et al. 2012a, Miller et al. 2013).

The barcode region has been useful for delineating species in various groups of parasitiform and acariform mites (e.g., Roy et al. 2009, Knee et al. 2012a, Glowska et al. 2014, Doña et al. 2015, Ondrejicka et al. 2016, Fisher et al. 2017). In Canada, approximately 60–70% of 230 morphologically recognized species of oribatids across 45 families are currently supported by barcode clusters (M Young and L Lumley unpubl. data). The rapidly growing barcode reference library for the Acari of Canada is therefore of considerable use. However, the most important and possibly most onerous step, the association of DNA sequences with morphological concepts, has to be addressed for most taxa in order to test the effectiveness of barcode-based species identifications. To strengthen analyses, a multigene approach should be favoured in the future, especially given the fast development of next-generation sequencing technology (Marcus 2018). With such increasing ease in obtaining sequences, it is more critical now than ever to build morphologically verified voucher libraries that will enable sequencing results to be taxonomically and ecologically meaningful.

Like almost all biota of this previously largely ice-covered country, the acarofauna of Canada has been recovering from glaciation since ice sheets began retreating ~14,000 years ago (Menounos et al. 2017). Consequently, determining which species have been introduced through recent human activity is often impossible, complicated by a lack of geographic, taxonomic, phylogenetic or host data (Langor et al. 2009, Beaulieu and Knee 2014). Even cases of mites specific to animal or plant hosts that have been introduced may present difficulties, because of uncertainties in the mite species boundaries, the actual host range, or biogeographical history of the host (Mironov et al. 2005, Navajas et al. 2010, Miller et al. 2013). Undoubtedly, many mite species have been inadvertently introduced to Canada with soil or water ballasts emptied near ports; with vertebrate hosts introduced intentionally as livestock, as pets or for hunting, or accidentally with imported goods, e.g., rodents (Navajas et al. 2010); and with invertebrate hosts on which they are parasitic or phoretic, such as fly pests, wood-boring beetles, or dung beetles introduced to accelerate decomposition of cattle dung (Humble and Allen 2006, Floate 2011). Widespread agricultural pests, such as the two-spotted spider mite, and many of the cosmopolitan mites breeding in stored grains, insect or fungal cultures, or bee hives (e.g., Varroa, Acarapis spp.), clearly originate from outside Canada (Langor et al. 2009, Beaulieu and Knee 2014). A few species have been intentionally introduced for biocontrol of agricultural pests or weeds (McClay and De Clerck-Floate 2013). In Europe, 96 species of mites have so far been identified as adventive, most of which are associated with agricultural commodities (Navajas et al. 2010). Given international plant trade, and the small size, cryptic habits and dispersal potential (e.g., phoresy, wind) of mites (Navajas et al. 2010, Beaulieu and Knee 2014, NAPPO 2014), we can expect a considerable number of non-native mites to be present already in Canada, and that their numbers will increase.

Ticks, the most infamous mites of all, are obligate blood-feeding ectoparasites of terrestrial vertebrates, primarily birds and mammals, but also reptiles and amphibians. Ticks are major threats to wildlife and public health, as they can harm their hosts through exsanguination, paralysis, and transmission of pathogens, including the causative agent of Lyme disease, Borrelia burgdorferi (Nicholson et al. 2009, Lindquist et al. 2016). The recent handbook to the ticks of Canada by Lindquist et al. (2016) represents a much-needed update from Gregson (1956) and includes identification keys to all instars as well as information on the species’ life histories, distributions, hosts, and pathogens transmitted.

The known diversity of Ixodidae, or hard ticks, in Canada has increased from 26 in Lindquist et al. (1979) to 41 species (Table 2). However, from this number, approximately 10 Amblyomma and five Ixodes species represent extralimital records. These species have been reported primarily from migratory birds and, therefore, it is unlikely they have established year-round populations in Canada (Scott and Durden 2015a, b, Lindquist et al. 2016). In the past 20 years, the blacklegged tick, Ixodes scapularis Say, a major vector of the agent of Lyme disease, has significantly expanded its range northward from the USA and has become established from Manitoba to Atlantic Canada (Leighton et al. 2012).

Argasidae, soft ticks, are generally nocturnal and more rapid feeders than ixodids, and mainly parasitize bats and birds. The number of known species in Canada has not changed since Lindquist et al. (1979), remaining at seven. However, over half of known argasid species are represented by only one or two records, suggesting that this apparently poor diversity may be in part a result of the lack of study in the country (Lindquist et al. 2016). The absence of BINs generated for Argasidae in Canada supports this hypothesis (Table 2). In contrast, a majority of Ixodidae has been studied molecularly, with at least 26 of the 34 BINs generated assigned to named species (Ondrejicka et al. 2016). It is expected that a few additional species of ticks in both families will eventually be found or recognized in Canada (Table 2).

This order of mites includes the most diverse group of predatory arthropods in soils and other detrital habitats (e.g., rotting wood, dung, carcasses, nests), a large component of plant-dwelling predators (mostly Phytoseiidae), as well as various lineages of vertebrate parasites (within Dermanyssoidea) and arthropod symbionts including numerous species that disperse phoretically on their hosts. Mesostigmata (= Gamasida) represents the bulk of the Parasitiformes, with 650 species in 46 families currently recorded in Canada, compared to 473 species in 1979, with many more unrecorded (Table 2). An additional eight families are represented in Canada by undetermined species. Taxonomic knowledge has strikingly improved for the bird-parasitic family Rhinonyssidae (Knee and Galloway 2017b) and significantly for Phytoseiidae (Denmark and Evans 2011), Trematuridae, Digamasellidae, Macrochelidae, and Laelapidae, although records for the latter five families are largely based on unpublished CNC specimen data. We anticipate an overall diversity of more than 1600 species of Mesostigmata, of which at least 60% are to be identified.

Molecular work generated 1409 BINs from 36 families of Mesostigmata (Tables 1, 2), most of which are not assigned to named species. These data indicate high genetic diversity that contrasts with our morphology-based assessments for the families Parasitidae (123 BINs), Digamasellidae (181), Ascidae (131), Blattisociidae (85), Phytoseiidae (320), and Laelapidae (155). For instance, the number of BINs for Phytoseiidae is almost twice the total number of known and unrecorded (estimated) species.

Sphaerolichidae and Lordalycidae were previously included in the Endeostigmata, in part based on superficial resemblance, but were later transferred to Trombidiformes (OConnor 1984), as they share derived characters with Prostigmata. Molecular work supports this relationship (Pepato and Klimov 2015), and at least Lordalycidae may belong within the traditional Prostigmata (Klimov et al. 2018). These small, globular mites are common in soil, litter and moss worldwide but are rarely studied. The presence of fungal materials in the guts of some of these animals suggests that they are fungivorous (Theron 1979, Walter 1988b). However, it has also been theorized that members of Sphaerolichus are ambush predators (Walter et al. 2009). Lordalycids have been collected across Canada, but have not been identified (Table 3). Sphaerolichids, in contrast, are known from just two undetermined specimens from Quebec. A couple more species may be expected for each family.

Prostigmatans display an exceptional diversity of lifestyles and ecological niches, and include herbivores (e.g., Tetranychoidea); fungivores (e.g., many Tydeoidea, Heterostigmata); an array of (proven and putative) predators in soils, on plants, and in fresh and marine waters; arthropod symbionts; diverse lineages of invertebrate (Parasitengona, some Heterostigmata) and vertebrate parasites (e.g., Cheyletoidea, Myobiidae). Based on species records alone, taxonomic knowledge has most notably improved since 1979 for Rhagidiidae, Tydeoidea, Hygrobatoidea, Cheyletoidea, Myobiidae, Stigmaeidae, Tetranychidae, and Tarsonemidae. There are currently 1100 species of Prostigmata recorded in Canada (increased from 800 in 1979), belonging to 86 families (Table 3). This excludes the Eriophyoidea, which, based on recent data (see Bolton et al. 2017, Klimov et al. 2018), appears to belong to Sarcoptiformes. An additional 12 families of Prostigmata are represented in Canada, although by as yet undetermined species, and 10 other families are anticipated. A total of 13 families represent new records since 1979, four of which are based on undetermined material only.

Molecular work yielding barcodes has produced 3261 BINs for 62 families of Trombidiformes (Tables 1, 3). For many families, the number of BINs is well above predictions of total species richness based on morphology, particularly Bdellidae (169 BINs), Cunaxidae (96), Eupodidae (520), Rhagidiidae (165), Tydeidae (217), Anystidae (61), Erythraeidae (313), Trombidioidea (122), and Pygmephoridae (112). We estimate a total diversity of over 3200 species of Prostigmata in Canada, about two thirds of which are yet undocumented.

Heterostigmata comprises seven superfamilies, all represented in Canada, many with highly specialized symbioses with insects (Kaliszewski et al. 1995, Walter et al. 2009).

Endeostigmata represents an early-derivative assemblage of tiny, soft-bodied mites (Walter 2009b). The group is probably not monophyletic and is not well understood phylogenetically, such that its infraorders and superfamilies remain tentative (Pepato and Klimov 2015, Bolton et al. 2017). Since 1979, it has undergone significant classification change, including some family names (Pachygnathidae is now Alycidae), although most constituent genera and families remain the same. The most extraordinary change here is our provisional placement of the Eriophyoidea within Endeostigmata, following recent molecular and morphological evidence that suggests a close relationship between Eriophyoidea and the endeostigmatan family Nematalycidae, both of which consist of worm-like mites that feed on fluids (Bolton et al. 2017, Klimov et al. 2018). In contrast, most sarcoptiform mites swallow particles of food and form discrete gut boluses, although fluid-feeding occurs insome Endeostigmata (e.g., Nanorchestidae, Alycidae: Bimichaelia) and several lineages of parasitic Astigmata.

A total of 176 BINs is assigned to at least four families of Endeostigmata (Tables 1, 4), but BINs for Eriophyoidea were not assigned to family level because the families of most specimens need to be verified. Except for Eriophyoidea, which has relatively few BINs compared to known and anticipated species diversity, the other families of Endeostigmata with molecular data (Alycidae, Nanorchestidae, Terpnacaridae) show a contrastingly high number of BINs compared to total expected diversity as inferred from morphological assessment.

Oribatids represent the core lineage of Sarcoptiformes. The numbers presented in this section do not include the hyporder Astigmata, which is taxonomically placed within the infraorder Desmonomata (Norton 1998, Schatz et al. 2011). Due to significant life history differences of the Astigmata compared to the rest of the Oribatida, Astigmata is considered separately (see next section). Oribatid mites inhabit many habitats in addition to their traditional soil-litter environment, such as freshwater (BehanPelletier and Eamer 2007) and marine littoral (Pfingstl 2017), and canopy habitats (BehanPelletier and Winchester 1998, Lindo and Winchester 2007). They are also the dominant arthropods in peatlands (BehanPelletier and Bissett 1994, Barreto and Lindo 2018). Based on their feeding behaviour as a group, they have been referred to as selective generalists (Schneider and Maraun 2005) to reflect the opportunistic feeding strategies of many species within their detrital environment, contributing to decomposition and nutrient cycling processes. Oribatid mites are predominantly detritivore-saprophages, variously feeding on detritus, fungi, algae, and other substrates associated with decaying organic matter, although predation of nematodes is also common. Unique among the Acari and other arthropods is a high prevalence of asexual (thelytokous) reproduction (~9% of species studied), with families or genera for which only females are known (Cianciolo and Norton 2006). Most surprising, however, is the re-evolution of sexual reproductive modes (Domes et al. 2007) arising from within asexual groups, the best example of which is the sexual hyporder Astigmata from within the asexual Desmonomata (Norton 1998). Whether sexual or asexual, many oribatid mites are long-lived for invertebrates (1–7 years; BehanPelletier 1999), with slow development and low reproductive rates (iteroparous).

Despite soil biodiversity in general being relatively understudied (Eisenhauer et al. 2017), the Oribatida have historically been, and remain, one of the better-known groups of soil acarines in Canada, due to concerted sampling efforts. This includes the works of N Banks in the earlier 20^th century, as well as some more contemporary sampling efforts by M Hammer (1950s), VG Marshall and colleagues (1960–1970s), M Mitchell (1970s), RA Norton (1970–1980s), and VM Behan/BehanPelletier (1970s–present). Sampling continues to focus on Oribatida, likely due to their charismatic morphology, high diversity, and life-history traits (e.g., K-strategists) that allow them to be included as bioindicators in environmental monitoring. Notable are the extensive works of BehanPelletier and colleagues, including west coast canopy sampling by Z Lindo, and the efforts of DE Walter and colleagues in conjunction with the incorporation of Oribatida into current monitoring programs such as that of the Alberta Biodiversity Monitoring Institute (ABMI) (Walter and Latonas 2012, Walter et al. 2014). Oribatid mites have also often been used for general ecological studies of human and/or natural disturbance (e.g., forestry, agricultural, or industrial practices), and as model taxa for diversity studies (e.g., BehanPelletier 1999, Battigelli et al. 2003, Déchêne and Buddle 2009, McAdams et al. 2018).

Marshall summarized the Oribatida in the Acari section by Lindquist et al. (1979) and reported 71 (+10 expected) families and 354 described species in Canada, with an estimated total diversity of 1554 species. Marshall considered nearly all families (except Kodiakellidae from coastal British Columbia) as probably transcontinental, and the majority of families to have a northern latitudinal range, either to treeline (nine families), to within the Arctic (32 families), or to High Arctic (nine families). The remaining 30 families were considered restricted to southern latitudes. In comparison, of the 100 currently documented or anticipated families in Canada, 44 families are represented in most or all ecozones including the Arctic, 47 families are restricted to boreal and southward, and the remaining nine families are known from only a few ecozones but ranging from southern Canada to as far north as Taiga or Arctic ecozones (Table 5).

Records of Oribatida of Canada up to 1986 were also captured in the Catalogue of the Oribatid Mites of Canada and the USA (Marshall et al. 1987), wherein was listed ~300 spp. from 160 genera from published records from Canada. Updates to species and distributional records by province, through to the early 2000s, are available online through the Diversity of Oribatida in Canada (DOC) website (BehanPelletier and Eamer 2004).

A total of 592 described species from 84 families are recorded in Canada, a 67% increase since 1979 (Table 5). Another 1267 species are expected to be recorded in the future, approximately 300 of which represent undescribed species or morphospecies currently in collections that need identification or verification. An additional 15 families are known in Canada, based on unidentified specimens, and Lohmanniidae is anticipated to be found. As many as 27 families, including 12 with undetermined species only, represent new records since 1979. The 99 families known in Canada represent 58% of the known world families (currently 172; Norton and BehanPelletier 2009). The families with the highest documented diversity in Canada include (Table 5): Ceratozetidae (53 species), Brachychthoniidae (38), Punctoribatidae (35), Eremaeidae (32), Phthiracaridae (28), Crotoniidae (24), Damaeidae (23), and Oribatellidae (22). Several of these groups have been extensively reviewed by BehanPelletier for North America (Ceratozetidae, Punctoribatidae, Eremaeidae, Damaeidae, and Oribatellidae) and those works contain keys to genera and species (references listed in Table 5).

Families where the number of species has substantially increased since Lindquist et al. (1979) are the Euphthiracaroidea, Crotoniidae, Eremaeidae, Carabodidae, Oribatellidae, and Scheloribatidae (Table 5). Increased species richness in these families is in part due to the taxonomic efforts of VM BehanPelletier, M Colloff, M Reeves, and W Niedbała, concomitant with the exploration of previously unexplored habitats (e.g., canopy habitats). On the other hand, reductions in the number of species in some families (e.g., Suctobelbidae, Oribatulidae) are mostly due to revisions in our understanding of the species concept and/or reassessment and placement of species into other taxonomic groups based on new diagnoses.

Molecular data (BINs) suggest that a large portion of the Canadian oribatid diversity remains undescribed or at least unrecorded, with a total of 2429 BINs recorded across 67 families surveyed so far (Tables 1, 5). However, there are discrepancies between the number of BINs and morphology-based identifications for several families of Oribatida, notably Oppiidae (144 BINs), Tectocepheidae (131), Oribatulidae (175), Scheloribatidae (184), and Ceratozetidae (245). For instance, the low diversity of recorded Tectocepheidae (three known spp.) is in contrast to 131 BINs, despite Tectocepheidae containing only two known genera with a total of 16 described species worldwide (Subías 2004). Within this family, known species in Canada reproduce via thelytokous parthenogenesis, and the number of BINs may indicate high within-lineage diversification (Fontcuberta Garcia-Cuenca et al. 2016). It is interesting to note that while Ceratozetidae has the highest number of described species (53 species) and Punctoribatidae, a closely related family, has similarly high diversity (35 species), the number of BINs recorded for Ceratozetidae is 245 while there are only 35 BINs for Punctoribatidae.

Taking into account the increase in discovered and described species over the last 40 years and the high number of BINs recorded so far, we estimate the diversity of Oribatida in Canada to be at least 1800 species, and possibly as many as 3000 species, with at least two thirds yet unrecorded (Table 5). A comparison of the Canadian oribatid fauna with a recent publication by Krisper et al. (2017) on the Oribatida of Austria, where they document over 677 species, supports the assertion that much of the Canadian fauna is still unknown, given that Canada has ~120 times the area of Austria and contains many more ecozones.

The Astigmata originated within the oribatid lineage, Desmonomata, and then radiated morphologically and ecologically, adapting to a remarkable diversity of niches (OConnor 2009). Adult astigmatans are similar in appearance to immature oribatids, and hence this clade is thought to have arisen via neoteny. Their evolutionary success can be attributed in part to the evolution of a non-feeding deutonymphal stage for dispersal and for enduring adverse environmental conditions. These traits facilitated colonization of the patchy, transient habitats in which free-living astigmatans thrive, such as animal nests, decaying wood, carrion, fungal sporocarps, and stored products. Many species disperse on insects and have developed relationships with them beyond simple phoresy. Similarly, several lineages of Astigmata have evolved commensal and parasitic relationships with vertebrates, living on and in the skin, fur and feathers of mammals and birds (Psoroptidia: Sarcoptoidea and feather mites). Most non-parasitic Astigmata are assumed to be fungivorous or saprophagous, though vertebrate commensals may also feed on sebaceous oils (OConnor 2009). In Canada, we now know of 441 species of Astigmata from 43 families, compared to a mere 142 species in 1979 (Table 6). In addition, three other families are recorded in Canada, based on unidentified material. The concepts of several families and their placement in superfamilies have changed substantially since 1979. Canestriniidae (Canestrinioidea) was predicted to occur in Canada by Lindquist et al. (1979); we do not expect it to occur here, with the nearest known locality being in the southeastern USA (B OConnor pers. comm.).

The most notable improvements in taxonomy of Astigmata in Canada are for mites associated with the plumage and skin of birds (Analgoidea, Pterolichoidea) (Table 1). There are significant, mostly unpublished, additions in other families, especially Acaridae and Chirodiscidae. The case of feather mites demonstrates how little is known and published and how much work is left to do for the taxonomy of Astigmata in Canada: Galloway et al. (2014) published 118 new records for Canada and mentioned 38 undescribed species of feather mites from grassland birds in Alberta and Manitoba alone! Molecular work conducted for Astigmata in Canada has been relatively limited, with only 153 BINs generated from 19 families; most of these have not yet been confidently assigned to named species. The Acaridae is well represented, encompassing about one third of BINs for Astigmata. In contrast, many families are poorly represented by BINs, compared to the diversity of known or anticipated species. This may be in part due to the limited sampling of Astigmata, which typically live as symbionts of vertebrates or in cryptic, patchy habitats. We estimate that over 1600 species of Astigmata occur in Canada, most of which (>70%) are yet to be discovered.

The one family in Canada, Histiostomatidae, consists of filter-feeding microbivores associated with moist decaying substrates and aquatic microhabitats. In Canada, they have been found associated with decaying bulbs, pitcher plants, insect and worm cultures, as well as with insects such as bark beetles, bees, carrion- and dung-breeding flies on which they disperse. New records since 1979 include two new species phoretic on amphipods (Fain and Colloff 1990) and one described from sphaerocerid flies (Samsinak 1989). Only 21 named species are known from Canada, but four times that many are unrecorded or undescribed (Table 6).

Five families of Hemisarcoptoidea have described species recorded in Canada (Table 6). This group includes fungivores in stored products (Carpoglyphidae, Hemisarcoptidae, Winterschmidtiidae), on foliage and in bark crevices (Winterschmidtiidae), algivores in littoral habitats (Hyadesiidae), parasites of coccinellid beetles and scale insects (Hemisarcoptidae), and various associates of subcortical beetles (OConnor 2009). Some winterschmidtiids (subfamily Ensliniellinae) are obligate associates of Hymenoptera, and include a species described from leafcutter bees (Megachilidae) in Nova Scotia which feeds on moulds growing on pieces of leaves in the bee nests (OConnor and Eickwort 1988; Table 6). A recent revision of Chaetodactylidae has three new Canadian records of obligate cleptoparasites or parasitoids of leafcutter bees, including two new species (Klimov and OConnor 2008). In total, 17 hemisarcoptoid species are known from Canada and over 50 more species in these five families are expected (Table 6). A sixth family, Algophagidae, has at least one unidentified species in Canada, and a few representatives in the neighbouring USA from water-filled treeholes or tree sap flux likely occur here.

Ancestrally associated with vertebrate nests, this superfamily includes numerous nest-dwelling fungivore-detritivores, as well as forms that evolved parasitism in the hair follicles of their mammalian hosts (Chortoglyphidae, Echimyopodidae). In addition to inhabiting nests, they can be found on mammals (more rarely birds) or insects on which they are phoretic, as well as in litter and anthropogenic habitats such as house dust and stored products (a few Glycyphagidae, Aeroglyphidae, Chortoglyphidae) (OConnor 2009).

Three families have a total of 24 recorded species in Canada, including several new records of glycyphagids and chortoglyphids from rodent hosts such as muskrats, beavers and mountain beavers since 1979 (Table 6). Rosensteiniidae, associated with bats and their guano, is newly recorded from southern Canada, but as an undetermined species. Echimyopodidae and Euglycyphagidae are anticipated for Canada. Overall, an additional 32 species of glycyphagoids are expected for Canada (Table 6).

The family Acaridae is the most diverse family within the Acaroidea at both the global and national levels. It is agriculturally the most important group of astigmatic mites because of their role as pests of bulbs, greenhouse vegetables, and stored products (e.g., grains, cheese, meat), where they can feed directly on the cereal grain itself or on green plant tissues (Sinha 1979, Beaulieu and Knee 2014). Most acarid mites are fungivore-saprophages and breed where fungi and other microbes abound, including soil and patchy habitats such as compost, rotting wood, tree bark, bracket fungi, phytotelmata, beetle galleries, and hymenopteran and avian nests. Some Acaridae and Suidasiidae feed on pollen inside bee nests in Canada. There are only a small number of scattered Canadian records of Acaridae and other Acaroidea published since 1979 (often identified only to genus level). Over 40 additional species are expected in Canada, mostly of Acaridae (Table 6). One family, Gaudiellidae, associated with bumble bees, has been newly recorded since 1979. The superfamily is in dire need of revision.

The sole family, Hypoderatidae, comprises parasites of birds and desert-dwelling rodents (OConnor 2009). This family was not recorded from Canada in 1979 but since then one species has been recorded from the skin of a kingfisher in Ontario (Pence and Gray 1996). Many of the species so far recorded from adjacent states of the USA are anticipated to occur in Canada on the same bird hosts (Table 6).

This group includes ‘fur mites’ (Chirodiscidae, Listrophoridae, Atopomelidae) which live in the fur of mammals and feed on sebaceous materials (OConnor 2009, Bochkov 2011). Other sarcoptoids obtain fluids from the skin surface (Myocoptidae, Psoroptidae), live in hair follicles (Rhyncoptidae), or burrow in the skin (Sarcoptidae) of their mammalian hosts. More invasive forms colonize the ears of various mammals (some Psoroptidae), nasal passages and lungs of rodents (Gastronyssidae, Pneumocoptidae), or the eye orbits and stomach of bats (Gastronyssidae). The effects of these mites on their hosts vary from relatively benign, such as the irritation caused by ear mites (Psoroptidae: Otodectes) of domestic animals, to highly detrimental, such as sarcoptic mange (caused by Sarcoptes scabiei [L.]) which can cause skin hyperkeratosis and hair loss and lead to population declines in domestic and wild mammals (OConnor 2009, Murray and St Clair 2017).

Five of the 12 globally recognized families of Sarcoptoidea are known in Canada and four others are anticipated to occur (Table 6). Currently, 38 species are recorded from Canada, more than double that recorded in 1979. Chirodiscidae experienced the largest increase since 1979, with 10 of 11 species currently recorded being restricted to beavers (Table 6; CNC). Eight more species of Schizocarpus may occur on beavers in Canada (Fain and Whitaker 1988, Bochkov 2010). Other new Canadian records since 1979 are from mustelids (Chirodiscidae), small rodents (Myocoptidae, Listrophoridae), rabbits, and bovid and cervid hosts (Psoroptidae). Representatives of four families not yet recorded in Canada are expected to occur here, based on nearby USA records: Atopomelidae, Rhyncoptidae, Pneumocoptidae, and Gastronyssidae. Overall, approximately 50 additional species are expected to be found in Canada (Table 6).

With 280 species from 25 families recorded (Table 6), these two superfamilies represent almost two thirds of all known species and more than half of the families of Astigmata in Canada. They dominate the diversity of acarofauna living on birds, with up to 10 species recorded from a given host species in Canada (SV Mironov, HC Proctor, and TD Galloway unpubl. data). Most families consist of the true “feather mites”, which are mostly paraphagous commensals, feeding on uropygial gland secretions, as well as on fungi and other organic material (algae, pollen) found on the feathers (Proctor 2003, OConnor 2009). A few families include true parasites that feed on or in the skin (Dermationidae, Epidermoptidae, Knemidocoptidae, Laminosioptidae), consume pith inside quills (Ascouracaridae, Dermoglyphidae, Syringobiidae), or eat live tissues in respiratory tracts (Cytoditidae, Turbinoptidae). Some of these mites significantly affect their wild and domestic hosts, causing dermatitis, scaly-leg and -face diseases of birds, or possibly weaken feather quills after feeding on the inner pith (Proctor and Owens 2000, Proctor 2003). Pyroglyphid mites are unique among the Analgoidea in that most species live as scavengers in the nests of their hosts (birds and mammals) rather than on their bodies, eating skin flakes, hair, and other organic debris. Some pyroglyphids (Dermatophagoides spp. and other dust mites) have adapted to living in houses where they feed on shed human skin that has been colonized by fungi, and are the culprits behind many respiratory allergies (Colloff 2009). Taxonomic knowledge of the two superfamilies in Canada has grown an order of magnitude since 1979, thanks to the work of Mironov, Proctor, and Galloway. The known fauna increased from a mere two to 65 species of Pterolichoidea and from 19 to 215 species of Analgoidea, with 12 of the 25 families in Canada representing new records for the country (Table 6).

Astigmatan feather mites, nasal mites, skin and quill mites are now recorded from at least 252 of the 690 bird species occurring in Canada (Lepage 2018), with a sampling bias for birds of the Prairie Provinces where most of the relevant research has been conducted (Galloway et al. 2014; Mironov, Proctor and Galloway unpubl. data). Most bird families that occur in Canada have been sampled for mites. Mironov, Proctor and Galloway have aimed for taxonomic breadth of hosts, which should parallel taxonomic breadth of mites. Most members of Analgoidea and Pterolichoidea known from Canada have been collected by washing the bodies of birds that were either found dead or that died in wildlife rehabilitation centres rather than by targeted collecting from particular species of birds. The most notable increase among families is for the world’s largest family of feather mites, Proctophyllodidae, the species of which inhabit wing feathers of passerines and hummingbirds (Galloway et al. 2014; Table 6). This is followed by the Analgidae, which inhabit downy feathers (Mironov and Galloway 2002). Next are the Alloptidae and Avenzoariidae, mostly associated with various aquatic birds (OConnor 2009; Table 6). The only Ascouracaridae recorded is a potentially host-specific quill mite collected from a threatened bird in Canada, the whip-poor-will (Caprimulgus vociferus Wilson). Families of mites that live on or in skin or in quills may be underrepresented due to sampling bias. Adult females of some species of Epidermoptidae are hyperparasitic on hippoboscid flies or lice and can be collected from these hosts, including two species recently reported from Canada (Knee and Galloway 2017a, Goater et al. 2018; Table 6). The family Pyroglyphidae may also be underrepresented since nests are less often targeted than birds.

Five additional families are anticipated in Canada (Table 6): Gaudoglyphidae, represented by one species living in the quills of domestic chickens (Bruce and Johnston 1976); Laminosioptidae, subcutaneous and follicular parasites (Skoracki et al. 2014); Apionacaridae, quill mites (Mironov 2001); Ptyssalgidae, hummingbird-specific quill mites (Atyeo and Gaud 1979); and Cytoditidae, inhabiting the nasal cavity, lungs or air sacs of birds. Based on a number of undescribed species at hand as well as their prevalence, level of host specificity observed so far, and the potential number of host species, we anticipate ~900 additional species of analgoids and pterolichoids on birds in Canada (Table 6).