The alpha temporal index measures the temporal distribution of species-naming efforts at different cells. AT assumes that cells with recent species names indicate ongoing taxonomic efforts, while cells with older species names do reflect efforts made in the past or the absence of new efforts – in the case that no recent names are present in the cell. To calculate this index, we fitted the year of description of each valid species name to an exponential decay curve, derived from a polynomial function of degree 4, considering the time span of all names. This curve provides higher weights to older species names; as taxonomy advances with time, the weight for descriptions decreases exponentially. Specifically, we assigned an alpha temporal value for each valid species name AT_sn (Eq. 1), based on the time elapsed from the most recent authorship year to the oldest (2023 to 1758 in our data), where species described in 1800 have values of ca. 0.5 and species described in 1900 ca. 0.1 (Fig. 2C, first graph).

AT _sn = (t_i − t_max/h)⁴, Eq. 1

where t_i is the year of authorship of the investigated valid species name, t_max is the year of the most recent authorship in the checklist of the valid species names and h is the maximum value of the difference between the years when the names were described. Subsequently, taking the values previously assigned to each valid species name (AT_sn), we calculate the average value of alpha temporal for each location (pi), based on the geographical occurrence of each species (Eq. 2).

AT _pi = μAT_sn(pi) Eq. 2.

AT values range from ~ 0 to 1; we assume that when AT ~ 0 or ≤ 0.25, it indicates that the majority of valid species names in a cell correspond to recent descriptions, meaning alpha taxonomy is predominant. Conversely, values close to ≥ 0.75 or 1 indicate that a large proportion of valid species names in a cell are old, meaning that alpha taxonomy is currently not predominant (Fig. 2D). This general interpretation helps summarising the history of local descriptions.

The Beta Proportion index measures the portion of synonymised species names in a given location. We assume that the most studied sites would have more synonyms per species because of the greater effort for thorough taxonomic revisions, although this is not a general rule in taxonomy because of the priority rule in the Zoological Code of Nomenclature (see Braby et al. (2024); https://www.iczn.org/). This index can be mapped, based on the known distribution of currently valid species, assuming that their associated synonyms share the same distribution ranges. Although this assumption may not hold valid in many cases, it does indicate the distribution of species that were recently revised, thereby making it appropriate as a proxy for beta taxonomic work. It is important to highlight that some species exhibit greater intraspecific variability, which can result in many synonyms, while others, with less heterogeneity in their phenotypic characteristics, have clearer and more easily distinguishable traits, leading to a lower number of synonyms. However, even less variable species may have been the subject of multiple studies due to different taxonomic circumstances. Additionally, the BP index is sensitive to species with a long history of nomenclatural changes (i.e. many synonyms) and a widespread distribution, which may overlap with species that have few or no synonyms and a more restricted, endemic range. In this context, the BP of a given region may reflect a potentially skewed pattern due to the partial or complete overlap of these species’ distributions, potentially distorting the beta taxonomy pattern in areas with few species. Nonetheless, by using this index, we assume that such issues are not widespread and have a minimal impact on our model, as this overlap is ultimately a reflection of the taxonomic history of a specific region or locality.

For each cell (pi), we calculated Beta Proportion using Eq. 3:

BP = 1 − [sn(pi)] / [tn(pi)], Eq. 3

where BP_pi is the result of 1 minus the ratio of the number of valid species name occurrences (sn) to the total number of name occurrences (tn) for each location (pi) and tn is the result of sn plus all associated synonyms for a given location (pi) (Stropp et al. in press) (Fig. 2C).

BP values range from ~ 0 to 1; BP ~ 0 indicates a low proportion of synonyms relative to the existing species at the location, suggesting that beta taxonomy is not predominant. In contrast, values close to 1 reflect a high proportion of synonyms, indicating that beta taxonomy is predominant. It is important to note that it is not possible to determine whether beta taxonomy is recent or older (Fig. 2D).

The accumulation of valid species names after World War II does not apply uniformly across all groups within this order. For instance, both the number of taxonomists and the rate of species descriptions have declined since the 20^th century for Acridomorpha, which comprises approximately 9,000 species (about one-third of all known Orthoptera species) (Amédégnato and Devriese 2008; Song 2010). This decline is also evident at the geographical scale, particularly in regions that were once supposedly well studied (i.e. yellow zones), but are now taxonomically neglected or lack trained taxonomists focused on local biodiversity. However, this may also be a sign of progress and that most species in this group are now described and undescribed species are less frequently discovered. More broadly, progress in taxonomy has been uneven across global regions and taxa (Stropp et al. 2022; Stropp et al. in press; Guedes et al. 2025), as exemplified in the present study on Orthoptera.

The accumulation of synonyms and the proportion of synonyms described per year have declined, particularly since the second half of the 20^th century. This trend likely stems from two opposing factors, which can influence the systematics of Orthoptera in different ways. On the one hand, certain regions (e.g. Europe and Southeast Asia) appear to have reached a consolidated knowledge as extensive phylogenetic studies and taxonomic revisions have been undertaken in recent decades which will have corrected many synonyms. On the other hand, in regions where taxonomy, arguably, remains in its early stages (i.e. grey areas), the decline may indicate a deficiency in synonymy detection, despite the ongoing description of new species. This limitation may introduce an additional source of uncertainty in biodiversity studies (Haila et al. 2014; Guedes et al. 2025), particularly in taxa and regions lacking comprehensive phylogenetic studies and taxonomic revisions (Guedes et al. 2020, 2023, 2025; Stropp et al. 2022). Moreover, it may affect macroecological and biogeographic patterns, as these analyses rely on accurate species lists and well-defined monophyletic groups (Isaac et al. 2004; Jones et al. 2012).

One significant factor influencing global taxonomy in recent decades is the availability and accessibility of online databases. Their benefits include maximising access to species descriptions, taxa distributions, data infrastructures and community discussions (Hobern et al. 2019). For Orthoptera, the most valuable database is the Orthoptera Species File (OSF), which had its initial version available online in 1997. To date, the OSF catalogues 30,206 valid species (including 29,294 extant species) and contains approximately 115,000 species images and 97,000 specimen records. In addition to online databases, an increasingly detailed species description, including high-quality images and DNA barcoding (Bisby et al. 2002), has contributed to a reduction in errors or gaps within alpha taxonomy in recent years. Consequently, fewer synonymies are being detected by beta taxonomy.

The increasing number of Orthoptera taxonomists over time results from various social and traditional factors. In some cases, it reflects the continuity of established taxonomic schools, where senior taxonomists often train networks of new taxonomists in specific taxa. Collaborative practice in taxonomy is also relevant (see Costello et al. (2012)), when it often involves field collectors sampling new species and senior taxonomists describing them in the lab. Ideally, in these cases, all of them are recognised as authors. Historical events have also influenced taxonomic activity. For instance, the First and Second World Wars led to a decline in both the number of taxonomists and the average number of species described per researcher (see Costello et al. (2012)). Similar impacts have been documented in the study of Chinese flora, global monocotyledons, European spiders and butterflies (Lu and He 2021) and fungi (Cunningham et al. 2024), consequently affecting the rate of documented synonymies.

The taxonomic status varies significantly across the world, depending on the taxa (Stropp et al. 2022; Guedes et al. 2025). Nonetheless, some general patterns can be inferred. In terrestrial vertebrates, for instance, tropical regions (e.g. the Tropical Andes, the Atlantic Forest in Brazil, Mesoamerica, the West Indies, eastern Africa, Madagascar, southern India and Sri Lanka and Southeast Asia) stand out due to the high number of taxa yet to be discovered and described. In contrast, most temperate regions, such as North America, Europe and northern Asia (e.g. Russia), have already documented the majority of their taxa (see Moura and Jetz (2021)). For invertebrates, the global scenario is more complex, given the vast number of undescribed species, particularly amongst arthropods, including millipedes, arachnids and insects (Mora et al. 2011).

For Orthoptera, the tropical regions contain the majority of recently described valid species, with fewer associated synonyms. This supports the previous hypothesis that these regions still require extensive taxonomic revisionary efforts (i.e. beta taxonomy), given the continued under-representation of their estimated species richness. On the other hand, temperate regions are dominated by older valid species names and a higher proportion of synonyms, reinforcing the idea that beta taxonomy is more prevalent in these areas.

The widespread distribution of areas with recent names and few synonyms reflects an emerging orthopteran alpha taxonomy, but little beta taxonomy, characterised by species discoveries which are not yet accompanied by comparing taxa across regions and refining their classifications through taxonomic revisions. This can be attributed to a historical shortage of taxonomists in megadiverse regions – the taxonomic impediment sensu Engel et al. (2021), which results in that, in particular for the richest taxa, species diversity has so far outpaced the available taxonomic expertise. Due to this, many tropical areas, such as South America, South-East Asia and Australasia, are currently undergoing extensive activity in alpha taxonomy. However, besides the lack of taxonomic research, this task is also hampered by the location of most of the reference natural history collections in countries from mainly temperate regions, which still store much of the material collected in tropical regions by early naturalists (Hawksworth 1995; Bakker et al. 2020; Raja et al. 2021; Weber 2021) (see Suppl. material 7: appendix S3, fig. S4A). This scenario can be understood as a taxonomic impediment, creating a logistic obstacle for researchers from tropical regions, who often need access to type material deposited in Old World collections to advance their taxonomic revisions (e.g. Raja et al. (2021); Nakamura et al. (2024); Suppl. material 7: fig. S4B). In the case of Orthoptera, the impact of this effect of scientific colonialism is partially minimised due to the availability of extensive type data (i.e. photos and drawings) within the Orthoptera Species File (OSF), compared to other taxonomic groups that lack these resources.

This contrasts with the situation in the historical centres of taxonomic research, as in Europe or North America, for instance, which are currently more active on beta taxonomy. These areas already hold a long history of taxonomic efforts, with a large number of taxonomic changes that result in a combination of older valid names and many synonyms. It is most likely that these regions are taxonomically saturated to some extent, with a significant proportion of their actual species richness already known, described and included in taxonomic reviews or catalogues (see Green (1998); Heller et al. (1998); https://www.grasshoppersofeurope.com/). Indeed, most temperate regions are taxonomically well-studied and thoroughly documented for the majority of the Orthoptera fauna (see Waloff and Popov (1990); Song (2010)). Thus, there the current focus is on either refining existing knowledge by describing species from remote areas and inaccessible habitats, such as caves and mesovoid soil substrate or conducting broader analyses on systematics and evolutionary relationships, using state-of-the-art techniques such as “omics” (e.g. phylogenomics, museomics or transcriptomics; Song et al. (2020); Kociński et al. (2021); Kim et al. (2024a)).

A large number of areas hold, on average, recent names and numerous synonyms. In these regions, the active research in both alpha and beta taxonomy couples the discovery of new species with taxonomic reviews and the publication of synonym lists. In some regions, such as in North America, these areas are adjacent to territories with older names and a large proportions of synonyms. This may indicate that, although regional checklists were previously thought to be complete (e.g. Song (2010)), the fine-scale exploration of these territories may still uncover previously unknown taxonomic gaps that end up in the discovery of new species (see Castro-Souza et al. (2024)). Such discoveries have likely been facilitated in the USA by the high presence of reference biological collections and the quantity of Orthoptera types deposited in their natural history collections (see Suppl. material 7: appendix S3, fig. S4A, B). In certain countries and regions, these taxonomic contributions stem from the enduring legacy of local senior taxonomists, who play a crucial role in training new taxonomists. This, in turn, helps sustain the tradition of Orthoptera taxonomy and ensures its relevance in these regions. In other parts of the Globe, some regions possibly reflect legacies of European colonialism in megadiverse locations (Weber 2021) or higher levels of international scientific collaboration. In any case, this level of taxonomic development is less concerning than that of areas where only alpha taxonomy has been conducted. Behind the large number of synonyms and recent valid names in these areas may lie studies utilising an integrative and more modern taxonomic approach, such as bioacoustics and/or molecular techniques (e.g. Braswell et al. (2006); Nattier et al. (2011); Husemann et al. (2013); Heller et al. (2017); Riede (2018); Uluar et al. (2021); Kim et al. (2024b)), which are based on novel criteria and species concepts that end up generating numerous taxonomic adjustments even in well-known species.

Very few areas hold a combination of older names and few synonyms, which indicates only past inventory effort, but little or no revisionary work. This may be due to two distinct, yet non-complementary, phenomena. In the best-case scenario, in these areas, current taxonomic knowledge comes from studies that produced classifications well-structured in terms of nomenclature and taxonomic relationships in the past, which have persisted until the present day, even with evidence coming from new taxonomic approaches. Alternatively, the current regional checklists in these regions come from taxonomic work conducted in the past that has not been revisited or revised later on. Importantly, a significant part of these areas is distributed in countries where socio-political impediments have occurred in the past or are occurring nowadays (Institute for Economics and Peace 2024). This not only hinders inventorying their biodiversity (Hanson et al. 2009), but also impacts taxonomy due to lack of trained taxonomists, low and discontinued investment and the discouragement of research and collaboration from international taxonomists due to high personal security risks and logistical issues (see Hilario-Husain et al. (2024)). This type of taxonomic status is the most critical, compared to the other types identified here and the areas holding it require strong attention from the taxonomic community. In areas lacking capacity or investment, these efforts could be facilitated by creating partnerships with local scholars and institutions (see Hanson et al. (2009)), even in the absence of regional Orthoptera taxonomists. Other areas holding such a status in impediment-free countries, such as Canada, Australia, New Zealand and some small parts of Europe (Institute for Economics and Peace 2024) correspond to spatial gaps within well-known regions and could be easily revisited by regional taxonomists.