Authors of all Biota of Canada papers were asked to provide data that were current at time of writing (late 2017 to 2018) rather than relying solely on the most recent published checklist. The sources of these data are included in individual papers. The total numbers of species currently known from Canada for each group (Table 1) were extracted from those papers, with the exception of the Zygentoma (Appendix I). For all groups, only the number of described species (not subspecies) currently recorded from Canada are included in the tally. These totals were reported by family in each individual paper but were totalled mainly at the order and higher levels herein (Table 1), with the exceptions that the former orders Psocoptera and Phthiraptera are now considered to be part of the Order Psocodea (see discussion in Anonby 2019).

The total number of described species currently recorded from Canada is 44,103 with 88.3% represented by insects, 10.3% by arachnids, 1.1% by entognathous hexapods, and 0.3% by myriapods (Table 1). Remarkably, the proportional representation by these four faunal groups in Canada is similar to that for the global terrestrial arthropod fauna of ca. 1.2 M described species (global calculations based on data from Zhang (2011, 2013), from references provided within the other papers in the Biota of Canada issue, and from many other sources). For terrestrial arthropods, the described Canadian fauna represents 3.7% of the known global fauna. The six most diverse terrestrial arthropod groups in Canada are Diptera (21.8% of total Canadian fauna), Hymenoptera (19.9%), Coleoptera (18.8%), Lepidoptera (12.4%), Hemiptera (9.1%), and Acari (6.8%).

Before comparing current described species diversity (Table 1) to that reported in Danks (1979b), it was necessary to adjust the earlier reported species numbers to correct some errors and inconsistencies that have recently come to light (see footnotes of Table 1 for the details of adjustments). Danks (1979b) reported 33,577 terrestrial arthropod species from Canada, excluding Tardigrada, Pentastomida, and terrestrial Crustacea, which were covered in the earlier work but not herein. The adjusted total of 32,850 described species known in 1979 (Table 1) is still somewhat inflated as the 1915 species of Acari reported then (Lindquist et al. 1979) included both described and undescribed species, but it is not possible to now adjust this number downward to accurately reflect only described species known at the time (see Beaulieu et al. 2019).

The number of described terrestrial arthropod species in Canada is now at least 11,250 (34.3%) more than that known in 1979. The groups with the greatest growth in number of described species are Hymenoptera (2729 spp.), Diptera (2564), Coleoptera (1560), Lepidoptera (1348), Acari (>1082), and Hemiptera (932). In terms of proportional growth in described species, the groups (all of them with relatively low diversity) showing the largest increases are Pauropoda (no species reported in 1979, currently 23 spp.), Pseudoscorpiones (500% increase, currently 25 spp.), Strepsiptera (333%, 27 spp.), Diplura (300%, 6 spp.), Protura (300%, 9 spp.), and Solifugae (300%, 3 spp.). Most of the groups showing little or no increase in described species during the last 40 years are small groups (<25 species in Canada); however, notably the Siphonaptera (154 spp. currently known from Canada) show only a 2.0% increase in described species, despite considerable work on this group during the last 40 years, indicating that the fauna was already well documented by 1979 (Galloway 2019b).

Approximately 37% of the described terrestrial arthropod fauna of North America north of Mexico occurs in Canada (estimate is based on data extracted from sources used in papers in Langor and Sheffield (2019), from authors directly via personal communications, and from other sources). The groups with the highest proportion of the known North American fauna present in Canada are: Ephemeroptera (51.1%; Jacobus 2019), Siphonaptera (50.8%; Galloway 2019b), Hymenoptera – Ichneumonidae + Braconidae + Chalcidoidea (48.3%; A Bennett pers. comm.), Odonata (45.8%; R Cannings 2019 pers. comm.), and Diptera (43.3%; Savage et al. 2019; A Borkent pers. comm.). Groups that have predominantly southern distributions in North America and have a low percentage of their fauna present in Canada include Scorpiones (1.1%; http://www.angelfire.com/tx4/scorpiones/states.html), Solifugae (1.5%; Cushing and Brookhart 2019), Diplura (3.5%; Sikes 2019), Diplopoda (4.4%; Langor et al. 2019), and Pseudoscorpiones (4.8%; Cameron and Buddle 2019).

The large majority of the Canadian fauna is restricted to the Nearctic; however, there is also a significant proportion that has a naturally Holarctic distribution. While the Holarctic component cannot be readily calculated for the entire fauna, it is relatively well known for some large groups: Lepidoptera – 4.8% (Pohl et al. 2019), Coleoptera – 5.1% (Bousquet et al. 2013), Hemiptera – 4.3% (E Maw pers. comm.), and Ichneumonoidea (Hymenoptera) – <5% (A Bennett pers. comm.). The Holarctic portion of the fauna is remarkably similar among these four highly diverse groups. In contrast, 21.9% of the 471 species of Collembola known from Canada have Holarctic distributions although it is not currently possible to discern what proportion of those are non-native versus naturally Holarctic (M Turnbull pers. comm.). Overall, we estimate that <5% of the total native Canadian terrestrial arthropod fauna is Holarctic. As more taxonomic revisions are undertaken that consider the Holarctic fauna, it will likely be discovered that for many groups some putative Nearctic species are synonymous with species described in the Palaearctic, thereby increasing the number of Holarctic species. Furthermore, other species currently considered Holarctic will likely to be discovered to be sibling species, one Palaearctic and one Nearctic, thereby decreasing the number of Holarctic species. Thus, the actual proportion of the fauna that is naturally Holarctic is likely slightly different from that currently estimated.

Many non-native terrestrial arthropod species have been introduced to Canada since the time of European colonization, most of them inadvertently and some intentionally, e.g., for biocontrol (Langor et al. 2009). The authors of most Biota of Canada papers considered and reported on the proportion of the fauna that is non-native. Two notable exceptions are the Diptera and the Hymenoptera. For these orders, the tally of known non-native species is based on information gathered from published literature and from consultation of taxonomists (D Langor unpubl. data); however, this database has not been updated since 2015 so it is likely that the numbers of non-native species are slightly under-estimated. In total, 2064 non-native terrestrial arthropod species (excluding Entognatha and Acari) are known from Canada and this represents ca. 5.1% of the total fauna (Table 1). The groups with the most non-native species are Coleoptera (639 spp.), Hemiptera (405 spp.), Hymenoptera (402 spp.), Lepidoptera (207 spp.), and Diptera (147 spp.). The groups with the highest proportion of their described fauna that is non-native are Zygentoma (100%), Dermaptera (67%), Mantodea (67%), and Blattodea (50%); these are mostly groups (with the exception of Mantodea) that have strong association with human dwellings, and many species have been transported around the world by human activities. For two groups, Acari and Entognatha, it is not yet possible to obtain good estimates of numbers of non-native species in Canada. The distribution of Entognatha (primarily soil-dwelling species and dominated by Collembola) is poorly understood and there are still serious gaps in taxonomy and distribution that prevent a meaningful assessment of which of the apparent Holarctic species are naturally Holarctic versus introduced. In the case of Acari, most groups are so poorly known in terms of taxonomy, distribution, biology, and phylogeny, that a meaningful analysis of geographic affinity cannot yet be undertaken (Beaulieu et al. 2019). The number of non-native parasitic Hymenoptera species is likely greatly underestimated, especially those that were intentionally introduced for the purposes of biocontrol as historical records are not complete (A. Bennett et al. 2019a). For most groups of terrestrial arthropods it is likely that additional non-native species already occur in Canada or may soon spread to Canada from established populations in the northern contiguous USA. Undoubtedly some species currently believed to be non-native may prove to have natural Holarctic distributions; however, it is conceivable that more than 2500 non-native terrestrial arthropod species are already established in Canada.

The immense physical size of Canada and the difficult and expensive access to large portions of the country (e.g., high latitudes and high altitudes) means that the vast majority of survey effort has been done in the south of the country and around major population centers and along major roads further north. This survey bias is exemplified by a map (Figure 2) of 81,555 collection points for the 375 species of Cerambycidae (Coleoptera) in Canada that were extracted from 106 Canadian and USA collections (see list in Bousquet et al. 2017). Even in southern parts of the country, there are habitats that are under-sampled for terrestrial arthropods. Thus, whenever there is concerted survey activity, the results in terms of new jurisdictional records can be astounding. For example, even following many years of sampling of Coleoptera in the Maritime Provinces, over 300 new beetle records were recently reported for New Brunswick (Webster et al. 2016). Similarly, sampling in Newfoundland and Labrador, mainly from 2008 to 2014, resulted in 119 new provincial records, six new Canadian records, and 34 new species of aleocharine rove beetles (Klimaszewski et al. 2011, 2016) and at least 90 new provincial records for other subfamilies of rove beetles (D Langor unpubl. data). As another example, a long-term survey effort in Waterton Lakes National Park since 2005 has resulted in many new Canadian and provincial records and new species of insects (Pohl et al. 2018; G Pohl, J Klimaszewski, and D Langor unpubl. data). Surveys of spiders in British Columbia, including at high elevations, in recent years have resulted in many new Canadian and provincial records (R Bennett et al. 2019b). There are many other examples of ongoing short- and long-term surveys in Canada that continue to yield new records of species. However, there are limited resources for surveying and the country is large, so prioritization and increased efficiency of survey effort is needed. Consideration should be given to where survey resources are best invested. Focus on biodiversity hotspots and threatened habitats (e.g., remnants of Carolinian forests and native grasslands), regions where there has been low sampling effort to date (e.g., alpine and subalpine zones, Arctic and Taiga ecozones), and undersampled habitats (e.g., hot springs, soils, saproxylic habitats, bird and mammal nests, and the bodies of vertebrates and invertebrates which are inhabited by many species, especially mites) may yield more value per unit of effort than further investment in surveys in areas and habitats that are relatively well sampled. There ought to be more discussion within the biodiversity community in Canada to prioritize and organize sampling efforts to make most efficient use of limited resources. This may also give direction and encouragement to growing numbers of citizen scientists who have the potential to immensely enhance biological surveys (see below).

Figure 2. 

Collection points for the 375 species of Cerambycidae (Coleoptera) in Canada based on 81,555 records extracted from 106 Canadian and USA collections (Bousquet et al. 2017).

In recent years, various survey initiatives have been developed to enhance sampling of biodiversity, including terrestrial arthropods. Since 2008, the Centre for Biodiversity Genomics (University of Guelph) has used its BIObus and teams to visit many biodiversity hotspots in Canada to sample specimens for DNA barcoding, and this effort has yielded hundreds of thousands of specimens and ca. 20,000 species (https://biobus.ca). Each year since 2007, the Alberta Biodiversity Monitoring Institute (ABMI) has systematically surveyed soil fauna across the province on a 20 km × 20 km plot grid, resulting in 400 soil samples each year from which invertebrates were extracted for monitoring purposes (T Cobb pers. comm.). This work has resulted in an enormous amount of information particularly about oribatid mite diversity and distribution (Walter et al. 2014). Furthermore, Bioblitzes have been organized by organizations such as the Biological Survey of Canada (eleven Bioblitzes since 2001; https://biologicalsurvey.ca) and Bioblitz Canada (35 Bioblitzes across the country in 2017 to mark the Canada 150 celebrations; www.bioblitzcanada.ca). Bioblitzes serve to bring together biodiversity experts and members of the public to focus on sampling the biota in a small region during a short period (normally 2–5 days). These have served to enhance surveys of the country’s biota, bring attention to the importance of understanding Canada’s biodiversity, and foster collaborations between professional biologists, students, and citizen scientists.

Another source of valuable specimens is from trap-based sampling programs established for a specific research or monitoring purpose. Frequently, only a subset of the taxa collected in experiments or for monitoring is utilized and the remainder (often called bycatch or residual) is discarded. Field sampling programs are expensive and often logistically challenging. Therefore, discarded specimens of non-target taxa represent missed opportunities to maximize return on investment, especially when such material is from regions and habitats that are generally poorly sampled. Clearly, saving bycatch has a cost in terms of additional processing time and storage, and when budgets are lean this additional cost can be prohibitive. However, there are also many people who are willing to make an effort to save some bycatch if they know that there is interest in the material by those who will make some effort to prepare and identify it and use the data. Where resource challenges could limit capacity to extract and store bycatch, creative solutions could be found through partnerships between those generating bycatch and those who have interest in it, e.g., through provision of funds for additional costs or in-kind supply of labour, to offset additional processing/storage costs. Opportunities to match supply and demand of bycatch require a communication network that serves as a clearinghouse service that connects people. An organization willing to perform this service could provide added benefit to survey activities in Canada.

Although historically the collection and examination of biological specimens has been the main source of data on presence and distribution of species, and remains the dominant source, increasingly photographs are yielding valuable information about the identity and location of species that on occasion reveals new jurisdiction records. Some of the best known initiatives that crowdsource data from primarily photos are iNaturalist (https://www.inaturalist.org/), which is global in coverage, includes plants, animals and fungi, and has nearly 90,000 users, and BugGuide (https://bugguide.net/node/view/15740) which is North American in scope and focuses on insects and other terrestrial arthropods. There are also initiatives that focus on particular taxa such as moths, e.g., Moth Photographers Group (http://mothphotographersgroup.msstate.edu/) and Mothing and Moth Watching (https://www.facebook.com/groups/137219092972521/). Within Canada there are several similar initiatives that are social-media-based and have much (or almost all) content focused on terrestrial arthropods, e.g., Alberta Bugs and Insects (https://www.facebook.com/groups/782992888444902/), Insects of Newfoundland (https://www.facebook.com/groups/717236451733098/), and NWT Species (https://www.facebook.com/groups/NWTSpecies/). As well, there are email listserves that have a similar purpose, e.g. Albertabugs and Albertaleps, both accessed through the University of Alberta. These initiatives serve two main purposes. First, they promote citizen science by encouraging public curiosity and information sharing and providing them with tangible rewards in terms of feedback from specialists concerning, e.g., identification and biological information. Secondly, on occasion photos reveal new or interesting records or natural history observations. However, identification depends on the quality of the photos and whether the species in question is identifiable based on a habitus, so only a small proportion of photos allow an accurate species determination. Thus, crowdsourcing of data through photographs will continue to provide a relatively small, albeit valuable, contribution to the future documentation of the Canadian fauna. However, through such citizen science initiatives that connect the enthusiastic public with appreciative and encouraging specialists, opportunities are created to encourage and train some ‘citizens’ to become more involved in surveys through the more traditional and data-rich method of collecting and preserving specimens to submit to specialists for identification. There are now cases where citizens who started as ad hoc sources of insect photos are now regularly collecting specimens that are contributing valuable records (G Pohl pers. comm.). The challenge is to encourage more specimen sampling by non-specialists by increasingly connecting specialists with the willing and capable public in mutually rewarding ways. While there is an investment required from the specialist to engage in training, provide some supplies (at least initially), respond to enquiries, provide identifications, etc., the potential for high return on the investment is excellent. More generally, the participation of enthusiastic specialists in public events such as Bioblitzes, science fairs, public lectures, natural history societies, school presentations, etc., and by creating products that have appeal to the ‘nature-curious’ public (e.g., field guides, websites, and videos), can potentially increase the participation of the public in natural science activities, including surveying of the biota.

For more than 41 years, the Biological Survey of Canada (BSC) has played important roles in promoting and fostering survey activities for terrestrial arthropods in Canada and synthesizing and distributing biodiversity information. The strength of the BSC is that it does not have institutional or departmental affiliation and therefore is not directed by top-down pressures to adhere to institutional or political agendas. As a network of frontline biodiversity workers, the collective expertise of the BSC self-organizes to focus on activities that fill important gaps in knowledge on Canada’s biodiversity. The BSC has rallied resources to focus on specific regions (e.g., Yukon, Haida Gwaii, the Arctic, and Newfoundland and Labrador), habitats (e.g., springs, ectoparasites of vertebrates), biotic communities (e.g., grasslands), and topics (e.g., non-native species) that have helped foster focused survey activities, resulted in significant products (e.g., books, scientific papers, newsletters), and greatly improved the state of knowledge of Canada’s terrestrial arthropod biodiversity (see Danks (2017) for the details of some of the accomplishments of the BSC). Particularly remarkable is the fact that in 1979 the BSC successfully engaged the Canadian biodiversity community to review the state of knowledge for terrestrial arthropod diversity in Canada, that resulted in the monograph Canada and its insect fauna (Danks 1979b), and is again doing so, 40 years later, through the current Biota of Canada initiative. There remain important roles for the BSC to play in promoting and coordinating national efforts to document the country’s biota in partnership with other biodiversity stakeholders. As it has no institutional constraints or political agenda, the BSC is well-placed to serve as a needs-driven, impartial broker and catalyst to continue to provide focus and foster activities on important knowledge gaps concerning the biota of Canada.

It is relatively easy, in terms of time and skills, to sample huge numbers of terrestrial arthropod specimens, especially using traps; however, it can be very time-intensive to identify them, even for taxa for which modern identification tools exist. DNA barcoding is increasingly helping with the identification process if the specimens are of sufficient quality to barcode and when there are comprehensive barcode libraries. However, DNA barcoding (or molecular approaches in general) is not a replacement for traditional morphology-based taxonomy but rather they are complimentary (Roe et al. 2017). Taxonomy has suffered steep declines in recent years in Canada, especially in universities (Packer et al. 2009, Archambault et al. 2010), which is also the global trend (Kim and Byrne 2006). It is therefore necessary to continue Canadian investment in taxonomy that integrates molecular, morphological, and ecological evidence to distinguish species, organize them within a phylogenetic structure, and develop identification tools (e.g., keys, molecular profiles). Without this, we will never be able to document, understand and protect the enormous biodiversity that surrounds us and on which we depend for environmental services and a sound economy.

Survey activities have resulted in accumulation of specimens in collections at a faster rate than they can be processed and identified to species, especially for groups where there are no Canadian specialists or modern identification tools. Canadian and foreign collections contain huge numbers of Canadian specimens that are not prepared or are identified only to genus or higher levels because there are insufficient people to do authoritative identifications and a lack of modern revisions and identification tools. Undoubtedly, a large proportion of the conservatively estimated 27,000 to 42,600 undocumented terrestrial arthropod species in Canada are already represented by specimens that have been collected and now reside in collections, either in containers of preserved, unprepared material or as prepared and labelled specimens. Furthermore, large numbers of valuable records of documented species, even in groups that are well known and have Canadian specialists and modern identification tools, have not yet been recognized because of the huge backlog in diagnostics. The Canadian taxonomic and diagnostic capacity is simply overwhelmed, and this is especially evident for highly diverse and relatively poorly known groups such as Acari, Diptera and Hymenoptera.

During the last 40 years, between 11,000 and 12,000 terrestrial arthropod species were newly documented in Canada (Table 1). With equivalent effort per unit of time in the future, and given that 27,000 to 42,600 additional species (even the upper limit is likely a conservative estimate) are waiting to be discovered, it will take 90–150 years for the fauna to be documented. Although molecular approaches will increase the rate of documentation of the fauna, it will still be decades before we know the identity of species in the country, let alone know their full distribution, habitat associations, etc. This is sobering, especially against a backdrop of rapid ongoing environmental change that is altering habitats and likely species viability in the country. Do we need to document all taxa and assign species names? Are measures of genetic diversity (e.g., BINs) sufficient for some hyper-diverse groups where there are few specialists and no impetus to study them because they are not sufficiently attractive or have little or no adverse effects on humans (e.g., cecidomyiid flies which have 1000–16,000 undocumented species in Canada)? What are the priorities for taxonomic investment? Should priorities be based mainly (or solely) on importance to agriculture, forestry and health as they are today? Can we better harness the potential of citizen scientists to engage in taxonomic/diagnostic activity? More fundamentally, is the value of documenting and understanding diversity in the natural world, the challenges, and trade-offs sufficiently understood by society, funding agencies, and policy-makers to allow appropriate prioritization and sound investment decisions? All of these and other questions require discussion across the full range of biodiversity stakeholders as we collectively try to find the most efficient way forward to document our Canadian biodiversity.

DNA barcoding has made significant contributions to biosystematics and the documentation of the Canadian biota, and its influence will grow as the DNA barcode reference library grows and more people use it to help reconcile taxonomic problems, improve diagnostic capacity and speed, and understand phylogenetic relationships. Already for terrestrial arthropods there are more than 75,000 BINs based on Canadian specimens, but there remains a large job of reconciling BINs with morphological concepts to understand the degree to which DNA barcodes reflect species and to build comprehensive voucher libraries. Improvement of protocols (e.g., better primers) that increase the success rate of barcoding attempts for certain groups (e.g., Brunke et al. 2019) will provide a better return on barcoding investment. Approaches that allow improved DNA recovery and amplification for older specimens and those collected using suboptimal techniques/preservatives will enhance data accumulation. Currently barcoding efforts have not been evenly distributed across the country and sampling equitability is needed to characterize the Canadian biota and its distribution. Especially promising is the rapid development of next generation sequencing approaches that readily allows sampling of many genes (in organelles and the nucleus) through ‘massively parallel sequencing’, and which will increase the utility of molecular data in defining species concepts and relationships and providing diagnostic tools (Roe et al. 2017).

The development of species checklists is but one facet of the broader realm of specimen and data management wherein there are other important considerations and needs concerning, e.g., biological collections, data standards, and data mobilization; however, these topics have been well covered elsewhere (e.g., Suarez and Tsutsui 2004, Johnson 2017). The values of species checklists and the particular needs of this activity, however, have not been sufficiently discussed and promoted.

Even though checklists are not included in this Biota of Canada Special Issue, most authors relied upon existing checklists or created their own as a basis for summarizing and analyzing species richness data. It is widely appreciated that species checklists, whether hard copy or electronic in nature, represent a useful means of synthesizing and sharing information about diversity and distribution of species. Since 1979, almost all of the most species-diverse terrestrial arthropod groups have been the focus of cataloguing efforts in Canada that have resulted in national checklists that show jurisdictional distributions and provide current nomenclature and classification, e.g., Maw et al. (2000) for Hemiptera (currently being updated; R Foottit pers. comm.), Paquin et al. (2010) for Araneae (with subsequent updates; see R Bennett et al. (2019a) for details), Bousquet et al. (2013) for Coleoptera, Pohl et al. (2018) for Lepidoptera, and A Bennett et al. (in prep.) for Hymenoptera. As well, in recent years, the National General Status Working Group has fostered the development of species lists for several orders of insects, including Ephemeroptera, Odonata, Plecoptera, Orthoptera, Neuroptera, Trichoptera, and Mecoptera as a necessary first step in assessing conservation status of individual species (CESCC 2016). Notably, Acari and Diptera, two of the six largest groups in the country, do not have national or provincial/territorial checklists. The state of knowledge of each these two highly diverse groups is too fragmented and preliminary to yet contemplate production of a national checklist for the entire group, although some portions (e.g., families) of these groups have been catalogued (Beaulieu et al. 2019, Savage et al. 2019).

Checklists of species, whether for a genus, family, order, or class, and whether national in scope or focused on a smaller geographic scale (e.g., province/territory, region, island, ecozone) or habitat, have high value. Checklist development requires synthesis of the body of evidence concerning diversity, classification and nomenclature, and therefore it represents a state-of-knowledge product. As a composite of collective knowledge, the process of creating a checklist tends to rally available expertise to collaborate and consider all available data and information. Checklists also fill federal, provincial and territorial needs as they are required by the NGSWG as the foundational first step in assessing conservation status of species, which is a national obligation. Furthermore, checklists serve to highlight gaps in the state of knowledge that can help prioritize future sampling and taxonomic endeavours. Finally, checklists provide a framework on which to organize new data (e.g., new records, new species, and changes in nomenclature and classification). Having a checklist that is publically available tends to challenge the biodiversity community (both professionals and citizen scientists) to improve on it, and this challenge usually engenders new sampling activity, makes it easy to determine if records are new, and encourages those with new records to make them known.

Checklists are outdated soon after they are published in terms of the included species, jurisdictional distribution, nomenclature, classification, etc. Soon after obtaining a newly published checklist, the knowledgeable user is soon filling the margins with notes concerning new and corrected information, and these notes summed across the community of users represent valuable improvements to the checklist. However, all notes and improvements are not usually available to all other users and thus the improvements of the checklist are not universally available until far into the future (usually decades) when the next edition of the checklist is published. Thus, to keep checklists current they need to be on-line and dynamic so that as new records (or other changes) are discovered, they are quickly vetted within the community of experts and incorporated. The development of virtual, dynamic checklists/catalogues in which to capture, organize and easily update information about Canada’s biota represents an exciting challenge. There are many interesting models already available in Canada and globally that could be emulated or modified, although it is beyond the scope of this paper to review these. The two largest challenges are, firstly, for the community of data suppliers and users to form a consensus on what is needed (content, functionality, etc.) and, secondly, to find the resources to develop and sustain it long term. Without a broad base of support from a diversity of partners, the development and long-term maintenance of dynamic checklists will likely not be sustainable.