As glaciers retreat, their forelands represent “natural laboratories” for the study of primary succession. This review describes how certain arthropods conquer pristine ground and develop food webs before the establishment of vascular plants. Based on soil samples, pitfall traps, fallout and sticky traps, gut content studies, and some unpublished data, we compare early arthropod succession on glacial forelands of northern Europe (Iceland, Norway including Svalbard, and Sweden) and of the Alps (Austria, Italy). While macroarthropod predators like ground beetles (Coleoptera: Carabidae), harvestmen (Arachnida: Opiliones), and spiders (Arachnida: Araneae) have usually been considered as pioneers, assumed to feed on airborne prey, this review explains a different pattern. Here, we highlight that springtails (Collembola), probably feeding on biofilm made up of algae or cyanobacteria, are super-pioneers, even at high altitudes and under arctic conditions. We also point out that macroarthropod predators can use locally available prey, such as springtails or non-biting midges (Diptera: Chironomidae). Pioneer arthropod communities vary under different biogeographical and climatic conditions. Two pioneer food webs, from northern Europe and the Alps, respectively, differed in structure and function. However, certain genera and orders were common to both. Generalists and specialists live together in a pioneer community. Cold-adapted specialists are threatened by glacier melting.

Spiders are important arthropod predators in many terrestrial ecosystems, and molecular tools have boosted our ability to investigate this taxon, which can be difficult to study with conventional methods. Nonetheless, it has typically been necessary to kill spiders to obtain their DNA for molecular applications, especially when studying their diet. We successfully tested the novel approach of employing spider faeces as a non-invasive source of DNA for species identification and diet analysis. Although the overall concentration of DNA in the samples was very low, consumer DNA, suitable for species identification, was amplified from 84% of the faecal pellets collected from lycosid spiders. Moreover, the most important prey types detected in the gut content of the lycosids were also amplified from the faecal samples. The ability to amplify DNA from spider faeces with specific and general primers suggests that this sample type can be used for diagnostic PCR and sequence-based species and prey identification such as DNA barcoding and next generation sequencing, respectively. These findings demonstrate that faeces provide a non-invasive alternative to full-body DNA extracts for molecular studies on spiders when killing or injuring the animal is not an option.

Since there is little known about invertebrates in glacier foreland succession, the aim of this study was (1) to characterize succession patterns of the epigean fauna, (2) to analyze how these are related to plant succession, and (3) to investigate the influence of locally varying environmental conditions. The Central Alpine glacier foreland of the Rotmoostal (Obergurgl, Tyrol, Austria) was selected as an example situated above the treeline (2280–2450 m above sea level) where a 2 km long deglaciated area covers a chronosequence of 140 yr. The epigean fauna was sampled in 70 plots of all ages and in nearby sites outside the foreland by pitfall trapping over the entire growing season in 1996 (June–October). Abiotic characterization and vegetation recordings were available for all plots. Rapid development of pioneer communities over 50 yr was followed by little change in older stages. Further development towards the mature invertebrate communities characteristic of areas outside the foreland only occurred on the sunny slopes near the terminal moraine and proceeded in a qualitatively different way. Sites in the alluvial outwash plain or otherwise physically disturbed were clearly successionally younger than adjacent undisturbed sites. The first colonizers were almost exclusively predators. Herbivores and decomposers appeared later. Similarities and differences between faunal and floral succession patterns are discussed. The major factors affecting faunal succession as identified by canonical correspondence analysis were soil formation and vegetation development along the chronosequence. In addition, favorable sun and light conditions may facilitate successional progress. Fauna communities also react to local conditions, most notably to the moisture/snow cover regime. Abiotic environment, architecture of plants, and plant species composition interact strongly as explanatory factors, but all three aspects also contribute significant unique correlations. There were no hints of random colonization patterns at the youngest sites. Pioneer invertebrate communities had the same small-scale spatial heterogeneity and equally strong correlations with environmental conditions as did the well-established communities at older sites. This leads to the conclusion that faunal colonization and succession in Alpine glacier forelands, to a large extent, follow predictable and deterministic assembly rules and that stochastic effects are of minor importance.