Silent killers among flowers: analysis of the ecological niche of three crab spiders (Arachnida: Araneae, Thomisidae)

Spiders are widespread generalist predators, principally insectivorous. Among them, crab spiders (Thomisidae Sundevall, 1833) are ambush predators, generally living on the ground or on plants, especially on their flowers. Previous studies have largely overlooked tri-trophic networks between spiders, their prey and the plants on which they hunt, especially at large spatial scale (e.g. national). This study aims to analyze, through Citizen-Science Data, the ecology of three Thomisidae species: Misumena vatia (Clerck, 1757), Synema globosum (Fabricius, 1775) and Thomisus onustus Walckenaer, 1805. Italian records of spiders with prey on plants were collected from the iNaturalist platform. Plants were identified at family level and prey at order level, except for Hymenoptera that were considered at family level. Analyses were performed separately for three main climatic areas of Italy, defined through three Koppen classes: Mediterranean, Temperate and Alpine climates. Species’ affinity with the three climate areas was analysed through a Principal Component Analysis. The trophic niche of the three spiders was studied with bipartite networks analysis. 627 observations of spiders with prey on plants were analyzed. Of these, 216 belong to M. vatia (34%), 222 to S. globosum (35%) and 189 to T. onustus (30%). Misumena vatia seems to be an Alpine-Temperate species, whereas S. globosum and T. onustus are more Mediterranean-Temperate spiders. The three species mainly hunt for Hymenoptera (especially Apidae) on Asteraceae plants. However, depending on the climatic area, variations in both structure and specialization in networks’ patterns were found. This study provides, for the first time, a large geographically-scaled overview on the ecological niche of three Thomisidae species, using simultaneously the two organisms with which they interact, i.e. plants and prey. This type of studies can be useful for assessing the impact of climate changes on trophic chains involving spiders.