Research interest in the Arctic is accelerating because of observed and anticipated dramatic climate change and its impacts on societies and ecosystems. Arthropods form a major part of the terrestrial species diversity in the Arctic, and are particularly sensitive to changes in the abiotic environment. Hence, increased research activity on Arctic arthropods would help towards conservation of Arctic biodiversity as well as in understanding the role of Arctic arthropods in ecosystem functioning. In this introduction to the special issue on Arctic entomology in the 21st century, we identify trophic interactions, biodiversity assessments, and taxonomic revisions as three important research fields in Arctic entomology. We also point to ways in which Arctic entomology could take advantage of recent developments in other research fields and we place the contributions to the special issue in a broader context. Arthropods form ideal model organisms in global change studies and there is a particular need for entomological studies from the dramatically changing Arctic. It is our hope that the papers within this special issue will be a valuable source of inspiration and may stimulate novel insights and achievements in Arctic entomology during the 21st century.

The High Arctic represents a unique environment, an environment from where knowledge is limited and which is currently experiencing rapid change. The archipelago of Svalbard in the European High Arctic possesses a terrestrial and freshwater invertebrate fauna that is distinctive and diverse. However, the majority of studies concentrate on the fauna of the comparatively mild west coast. Very few investigations of the colder east coast exist. Furthermore, scientific investigations are relatively recent. Scientific records of the terrestrial invertebrate fauna begin in the mid-19th century with species inventories and community descriptions but experimental field-based studies and physiological investigations did not commence until the 1980s. Some 570 articles consider this fauna, 54% of which have appeared since 1990. There is hence a dramatic and rapid increase in our understanding, which is not only improving our comprehension of Arctic ecosystem functioning but also providing a baseline for environmental change studies. Due to a largely pristine environment, a political focus and relative ease of logistics, Svalbard is set to become a focus of such studies. This article considers the state of knowledge of the terrestrial and freshwater invertebrate fauna of Svalbard, current research, and discusses the threats to the distinctive communities.

Arctia olschwangi Dubatolov, formerly known only from Arctic Siberia, Russia, is recorded from northern Alaska, United States of America. Distinguishing characters between northern populations of Arctia brachyptera Troubridge and Lafontaine, Arctia caja (Linnaeus), A. olschwangi Dubatolov, and Arctia opulenta (Edwards) are discussed. Arctia brachyptera Troubridge and Lafontaine is hypothesised to be a subspecies of A. olschwangi Dubatolov but more specimens need to be examined before this taxonomic change is made.

Arctic arthropods are essential prey for many vertebrates, including birds, but arthropod populations and phenology are susceptible to climate change. The objective of this research was to model the relationship between seasonal changes in arthropod abundance and weather variables using data from a collaborative pan-Canadian (Southampton, Herschel, Bylot, and Ellesmere Islands) study on terrestrial arthropods. Arthropods were captured with passive traps that provided a combined measure of abundance and activity (a proxy for arthropod availability to foraging birds). We found that 70% of the deviance in daily arthropod availability was explained by three temperature covariates: mean daily temperature, thaw degree-day, and thaw degree-day2. Models had an adjusted R2 of 0.29–0.95 with an average among sites and arthropod families of 0.67. This indicates a moderate to strong fit to the raw data. The models for arthropod families with synchronous emergence, such as Tipulidae (Diptera), had a better fit (average adjusted R2 of 0.80) than less synchronous taxa, such as Araneae (R2 = 0.60). Arthropod abundance was typically higher in wet than in mesic habitats. Our models will serve as tools for researchers who want to correlate insectivorous bird breeding data to arthropod availability in the Canadian Arctic.

Seasonal patterns in the taxonomic and functional structure of epigeic Coleoptera assemblages in wet and mesic habitats were studied in Kugluktuk, Nunavut, Canada. Using pan and pitfall traps, 2638 beetles were collected between 21 June and 13 August 2010. Fifty species (including 17 new territory records) in 11 families were identified. The biomass of each specimen was estimated, and each was assigned to a functional group. Species composition differed between habitats throughout the active season and there was a rapid compositional turnover even though species diversity was similar in both habitats and among sampling periods. The functional beetle assemblages in the two habitats were different, and both assemblages experienced seasonal turnover in function; this effect was more pronounced in the mesic habitats. The beetle fauna in both habitats was predominantly entomophagous. We also examined the influence of seasonal weather patterns on assemblage structure: there is a significant relationship between mean daily temperature and assemblage structure. This relationship indicates that changes in weather (or longer-term changes in climate) could affect the diversity and ecological function of insects in this system. Given the significance of insects in the north, this could result in important changes to northern ecology.

Outbreaks of geometrid defoliators in subarctic birch forest in Fennoscandia often occur at high altitude in a distinct zone along the tree line. At the same time, moth larvae may not have an impact on the forest at lower altitude. Directly adjacent outbreak and nonoutbreak areas offer unique opportunities for studying the underlying mechanisms of outbreaks. Within two altitudinal gradients in coastal northern Norway, we investigated whether altitudinal outbreaks might be caused by release from pupal predation by ground-dwelling invertebrates such as harvestmen (Opiliones), spiders (Araneae), rove beetles (Coleoptera: Staphylinidae), carabid beetles (Coleoptera: Carabidae), and other beetles (Coleoptera). We predicted a consistently higher abundance of such generalist predators at low versus high altitudes. Our results did not support this prediction. There was no consistent altitudinal variation in the abundance of predators that could be related to zonal moth outbreaks in the birch forest slopes. In addition, none of the predator groups investigated showed any numerical response to a distinct outbreak of winter moth that took place during the course of the study. Consequently, localised moth outbreaks at the altitudinal tree line in northern Norway cannot be explained by the release from pupal predation by the predator groups examined here.

Despite increasing worldwide interest in host–parasitoid food webs, the parasitoid communities of the high Arctic remain poorly explored. To allow analyses of global patterns, and to detect the effects of ongoing climate change, such data are urgently needed. In this paper, we describe a systematic effort to characterise the high-Arctic Hymenoptera and Diptera parasitoid community associated with Lepidoptera hosts of the Zackenberg Valley (74°30′N, 21°00′W), northeast Greenland. Here, we first sampled adult parasitoids by a combination of Malaise traps, pitfall traps, and, less extensively, yellow pan traps and sweep netting. We then identified the host use of individual parasitoid taxa by rearing a large number of host individuals and species across multiple years. We now describe our preliminary findings on the species diversity of the target community, on trophic links between hosts and parasitoids, and on the sampling effort and techniques needed to characterise the community. We report on 30 local parasitoid taxa representing four families, three of which are species new to Greenland. In describing the community, we make a specific effort to summarise what is known about the taxonomy, phenology, and host use of the component species, to the benefit of future research in the area.

A comparison is made between a three-year structured-sampling study that compared spider faunas of two tundra habitats and a single-year unstructured-sampling study, both within the Arctic Long-Term Experimental Research (LTER) field station at Toolik Lake, Alaska, United States of America. The three-year study documented 51 species and predicted a total of 60 species for the area. Our one season study documented 39 species, of which 24, or 62%, are not shared by the three-year study, raising the total count for the LTER to 75 species. These findings emphasise limitations of species richness estimation methods and help dispel the perception that Arctic tundras are homogeneous and species poor.

Comparisons of past and current butterfly species distributions are being used to gauge the effects of climatic change in various parts of the world. Historic butterfly records from Herschel Island, Yukon, Canada, presented an opportunity to do such a comparison in an Arctic tundra region known to have a diverse butterfly fauna. We compared historic species records (1916–1983) with newly collected ones (2007–2009) to assess possible changes in species distributions. Of the 21 species documented for Herschel Island, six were newly found and two were not reconfirmed. We postulate that warmer temperatures facilitated the apparent northerly range expansions of several species by making butterfly flight and dispersal possible. This is supported by interannual comparisons on a smaller time scale, 2007–2009. During this period, we observed accelerated butterfly phenology and higher relative abundance of butterflies associated with earlier snowmelt and with earlier and more intense early summer heating.