No abstract

More than half of all spider species hunt prey without a web. To successfully subdue their prey, they use adapted capture behaviour and efficient grasping mechanisms to interrupt the prey's locomotion, and to restrain it from escaping during the subsequent handling for final envenomation. In this study, we investigated how the prey capture behaviour of different lycosoid spider species is related to leg morphology and venom efficiency; using high speed videography, feeding experiments, stereomicroscopy, scanning electron microscopy and LD 50 venom bioassays. We found that different species employed different techniques when grasping their prey and these differences strongly correlate with the distribution and size of hairy adhesive leg pads (so-called scopulae on pro-and retrolateral parts of legs) and erectable spines, which act in a complementary way. Our results indicate that the grasping and handling behaviour and leg morphology is crucial in restricting the prey's movements. However, none of these traits is directly related with venom efficiency.

One key event in insect evolution was the development of mandibles with two joints, which allowed powerful biting but restricted their movement to a single degree of freedom. These mandibles define the Dicondylia, which constitute over 99% of all extant insect species. It was common doctrine that the dicondylic articulation of chewing mandibles remained unaltered for more than 400 million years. We report highly modified mandibles overcoming the restrictions of a single degree of freedom and hypothesize their major role in insect diversification. These mandibles are defining features of parasitoid chalcid wasps, one of the most species-rich lineages of insects. The shift from powerful chewing to precise cutting likely facilitated adaptations to parasitize hosts hidden in hard substrates, which pose challenges to the emerging wasps. We reveal a crucial step in insect evolution and highlight the importance of comprehensive studies even of putatively well-known systems.

Orb-weaving spiders (Araneidae) are commonly regarded as generalist insect predators but resources provided by plants such as pollen may be an important dietary supplementation. Their webs snare insect prey, but can also trap aerial plankton like pollen and fungal spores. When recycling their orb webs, the spiders may therefore also feed on adhering pollen grains or fungal spores via extraoral digestion. In this study we measured stable isotope ratios in the bodies of two araneid species (Aculepeira ceropegia and Araneus diadematus), their potential prey and pollen to determine the relative contribution of pollen to their diet. We found that about 25% of juvenile orb-weaving spiders’ diet consisted of pollen, the other 75% of flying insects, mainly small dipterans and hymenopterans. The pollen grains in our study were too large to be taken up accidentally by the spiders and had first to be digested extraorally by enzymes in an active act of consumption. Therefore, pollen can be seen as a substantial component of the spiders’ diet. This finding suggests that these spiders need to be classified as omnivores rather than pure carnivores.